# Nalon Viper 2.5cc CI Engine



## pat_pending (Nov 19, 2020)

Hi All,

after finishing the two Boll Aero 18s and a workshop covered in castor oil and several scars and cuts on my fingers, it's finally time to get going on my next engine. After a few recommendations I have decided to go for the Nalon Viper 2.5 using plans from the Motor Boys crew at modelenginenews.org.

Im spending a bit pf time up front modelling the plans out in CAD and doing the imperial to metric conversions there to make sure everything checks out and just 'getting my head around' making the parts and how things should fit. This engine is actually way more sophisticated than anything I've attempted before so I'm slightly daunted and excited at the same time. Looking forward to making some swarf and at the same time realistic that my scrap bucket might also see some additions.








They say the journey of a 1000 miles begins with a single step well I guess that is the purchase of some bearings!




Anyway the question I have for some people out there far more knowledgable in such matters than I am is per the picture below. Do I need to provide a bit of relief to ensure that the inner ring of the bearings doesn't rub on the crank web or the bearing seat or can I implement the plans exactly as drawn. I have crudely scribbled the areas on the plan where I think there may be interference below and would really appreciate a steer on whether this could cause issues/needs a bit of machining so nothing touches the inner ring. I have studied a bunch of plans and photos and it **looks** like there is no issue and the bearing seats can just be flat but wanted to ask the forum to see is there is a 'proper way' of doing this.

Also in the axial dimension, I assume the front split cone rides on the inner ring and pulls the inner rings and crank shaft tight against each other so they rotate together and cant slip on the shaft.

Thanks all in advance.

Patrick


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## Mechanicboy (Nov 19, 2020)

0,1-0,15 mm free play (0.0040"-0.0060")
To prevent scrubbing between rotating parts and house/crankshaft


.


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## pat_pending (Nov 19, 2020)

Mechanicboy said:


> 0,1-0,15 mm free play (0.0040"-0.0060")
> To prevent scrubbing between rotating parts and house/crankshaftView attachment 120885
> .View attachment 120886


Thanks Jens. That's exactly what I thought! Patrick


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## Ramon (Nov 19, 2020)

Hello Patrick, Congratulations on starting your new project 

Whilst a double ball race front end should have clearance it should not physically 'float' as such - that would mean the rear bearing is to loose on the shaft or too loose in it's housing.

It's best to have a small raised area in front of the web to sit against the inner race - no more than 0.1-0.15 and about the same diameter as the inner to give clearance on the rest of the web on the outer bearing. As Jens says when the front race is pulled up against the step on the crankshaft there should be about the same amount of 'free play' but of course if the fit is correct on the rear bearing you should not be able to move the crankshaft this amount by hand. i.e. Once the rear bearing is seated firmly in its housing with the shaft up close tightening the prop should not apply any pressure to the rear face of the front bearing housing but to the step on the crankshaft. If dimensions are a little tight and it does, it's just a matter of easing that face a little.

Looking forwards to your build in coming days

Regards - Ramon (Tug)


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## Ramon (Nov 19, 2020)

Hi again, I'm having real computer problems at the moment and things are very slow to load. 

Having posted I have just been able to see Jens drawing where he shows a slight relief for the inner race on the rear bearing.  I don't recall doing this on any of the engines I've built so far but it will of course allow the race to load so it's probably advisable to do so.


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## Ramon (Nov 20, 2020)

This image may be of interest Patrick - the shafts from the last engines made. You can see the relief on the web and the drawing top right


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## Jasonb (Nov 20, 2020)

Deleted wrong engine


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## pat_pending (Nov 20, 2020)

Ramon said:


> This image may be of interest Patrick - the shafts from the last engines made. You can see the relief on the web and the drawing top right


Great thanks Tug. V helpful.

Patrick


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## pat_pending (Nov 20, 2020)

Jasonb said:


> Deleted wrong engine


Surely no such thing as a wrong engine


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## Ramon (Nov 20, 2020)

Patrick, 
When Ron Chernich drew these out for MEN I believe he had an example of the original engine to guide him (or dimensions taken from one)

The drawings as such - particularly the GA are 'basic' in as much as no tolerance on moving parts are shown. Without checking the complete drawings I'm not certain if the due allowances are dimensioned on the individual parts. If not it's very much down to the builder to make the parts with the neccessary fits to suit their own preferences or from other guidance.

As you are aware this engine was originally intended for the Team Racing discipline of model flying and as such all efforts to maximise performance would have been made in the original. Attention to fits would have been paramount.

Take your time to get everything perfect 

Tug


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## Mechanicboy (Nov 20, 2020)

Ramon said:


> As Jens says when the front race is pulled up against the step on the crankshaft there should be about the same amount of 'free play' but of course if the fit is correct on the rear bearing you should not be able to move the crankshaft this amount by hand..
> 
> Regards - Ramon (Tug)



Ramon
There is not wrote "..the front race is pulled up against the step on the crankshaft.." in my comments where I drew arrows in the drawing has nothing to do with pulling the crankshaft in one direction, it is contact to contact where the ball bearing is mounted in place. Those who are not in contact are these rotating parts should not scrub against each other. Of course, the crankshaft should not travel longitudinally with ball bearing in crankcase due the split cone is locked together with the crankshaft on the front ball bearing so that it is prestressed on the rear ball bearing when the engine is new. During running-in, the ball bearings are adjusted to the correct tolerance in distance by expansion of heat in crankcase/crankshaft.


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## Ramon (Nov 20, 2020)

My apologies Jens - I was not quoting you directly but comenting on what I thought you were implying

I agree - the crankshaft is not 'pulled' as such other than by the propeller forces acting in one direction.

'End float' however could be mistrued as free movement which is not the case.

If the rear bearing is fully pressed home in it's housing there has to be a clearance at the front end of the shaft at the step on a two ballrace set up. When the propeller nut is tightened that would push the prop driver and split collet backwards against the bearing until the bearing hits the step on the crankshaft. There has to be some clearance behind that front bearing in it's housing otherwise binding will occur- which I think is what you are also saying

The fit of the front bearing in it's housing is usually of less tolerance ie tightness, than the rear fitting.This allows the bearing slight movement as the shaft expands/contracts with temperature variation which I assume you are referring to  in your last sentence.

Regards - Ramon


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## tornitore45 (Nov 21, 2020)

I think a general rule to go by is that when the two bearing are pushed against each other, by placing the shaft under tension by tightening the prop nut, no axial stress is put on the ball cages. The two inner races are located by shoulders on the shaft. In other words the outer races have some axial clearance so that are not clamped around the housing walls.  In other words eliminate any axial load on the bearing.


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## Ramon (Nov 21, 2020)

Hi Mauro,

When tightening the prop nut the action itself places no tension on the shaft itself. The collet is forced back to the bearing inner which in turn is forced back to the step on the crankshaft - it should have no influence on the rear bearing. Once this is in compression there should be a very small amount of clearance between the crankcase and the bearing inner of the front race.

Here's the GA drawing of my 5cc Oliver Tiger. It is drawn in the same manner as Patricks Nalon GA showing no tolerances. Each colour is a separate item/layer so when each in turn is taken to produce a working drawing for the part tolerances are then added as in the previous drawing posted. I can't find an image at the moment to show this.






Sorry to incur on your thread again Patrick but hopefully this will help in some way

Tug


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## pat_pending (Nov 24, 2020)

Thanks everyone. I think I understand the principle now and have the confidence to have a go soon. Work commitments and a bit of workshop remodelling (an organiser for my bar stock that is better than just chucked in a box) and a bit of fettling with the machines tightening gibs, tailstock alignment etc + some Mach4 gremlins preventing me from getting the most out of my laser cutter took the 'shed time' last week. I look forward to being able to make some swarf soon!

in the mean time, this is what the cad looks like:






and the stock organiser


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## Mechanicboy (Nov 24, 2020)

Look much better after some corrections.


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## Ramon (Nov 24, 2020)

Can't quite agree with Jens here as the front end as drawn still has the potential to crowd the front race. This is because of that small relief you show behind the inner ring. 

Unless the tolerances are _very_ exact, tightening the prop will force that inner against the balls and into the outer with considerable pressure. Whilst the relief shown behind the rear race inner is beneficial it is not so in the front. 

Have to say it again but I believe the front of the step should be a couple of thou in front of the rear face of the front housing. 

Regards - Tug


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## Tim Wescott (Nov 24, 2020)

Tug, if I'm understanding what you're saying correctly, should you also be recommending that the front housing be fit so that the outer race can move fore and aft, to find its own happy place?  Because otherwise it could end up loading the balls against the races just by how its positioned in the front housing.


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## Ramon (Nov 25, 2020)

Tim , Yes I did point that out previously (post#12).  Loading Crowding of the front race is very easy to do if the freedom isn't there

This issue came up on another forum some time back. An insistance that any twin bearing spindle should be preloaded  being stated . At first, I found it difficult to understand what was being said  but after doing some research on bearings could see what was being proposed but not how it could be achieved in this particular set up. It is clearly stated by bearing suppliers that for an ideal set up both races should be preloaded but difficult in this situation.

With this set up, as said, the ability to crowd the front race is there. As the case expands with temperature increase the effect is even more exacerbated. If the front race is a light push fit in the housing however with a small clearance behind such movement occurs without effect. Not perfectly ideal maybe but perfectly good enough for the thousands of commercial engines over the years done similar.

Since the issue was first raised I have often thought, though not attempted to do it, that if the front bearing outer was to seat against some resilient elastic material - urathane perhaps, possibly even an o ring - the compression of such would keep the front bearing in a degree of preload in the correct direction. Whilst it may work in the short term however I'm not convinced the o ring long term compressibility without permanent deformation would be suitable.

All the engines I have built so far have had this 'clearance' set up without any issues. Access to more precise machining (and measuring) methods not usually available to the home builder may potentially change matters of course.

Regards - Tug


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## Peter Twissell (Nov 25, 2020)

If one wanted to preload both bearings, it would be necessary to add a spacer between the inner races. This is not practical in a shaft valve 2 stroke design.


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## Ramon (Nov 25, 2020)

That was exactly my point to the person who suggested this on the other forum. Not practical at all unless one can load the front outer ring in the opposite direction to the load on the inner - hence my thought that, as the crankshaft is acting as the spacer - which for all intents and purposes it is - then possibly a tough resilient compressible material acting in the other direction on the outer ring _may_, potentially, have this effect.

I am not suggesting that this is the road to take - merely that it has a potential.  The twin ball race engines made so far  plus those odd commercial ones renovated (twenty plus) have all been set up as previously described with a very small clearance behind the front bearing.

The bearing fit on all is very smooth and free - obviously an important requirement - That they have all run and run well is all I can say to qualify my reasoning.

Tug


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## Tim Wescott (Nov 25, 2020)

@Ramon You could use a wavy washer to spring-load the thing.  Or maybe a really skinny Belleville washer.  Even once you're past the need for it to be custom-made, I can see all sorts of difficulties with getting the material and temper right so that it stands up under heat cycling and vibration, but you could _try_.

@Peter Twissell : From my understanding of how the whole preload thing works, you could space the outers out and the inners in, instead of the other way around, so Tug's notion of an O-ring would work for as long as the thing had some spring.

And, having worked in aerospace, I know there's some guy in the corner with an advanced degree and no concept of practical application who's thinking that if you make the case out of the same material as the crank, then the case and the crank together could be precision ground (or shimmed) to provide the right preload.  Never mind wear and thermal effects -- they'd convince the boss that it'll work, and if they've also got political chops the thing will actually get into production before people realize that it doesn't work over temperature.


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## Ramon (Nov 25, 2020)

Hello Tim, yes I guess a strong narrow banded wavy washer would work but my thinking on this is only just that - a thought. I'm pleased to see you refer to it as a notion  

So many engines have been set up 'the other way' I feel there's little to be gained in trying. If it was a really viable proposition then I'm sure it would have been done by many of the high performance engine manufacturers long before now which was the thrust of my reply to the original poster on the other forum.

The main object is to get the lower end as true as possible - bearings exactly concentric and parallel to each other with no hint of stresses to inhibit a truly free running shaft in the slightest. It's easy enough to achieve with home based kit but we'll leave that until Patrick gets there. He's got that case to make a start on first

Tug


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## mu38&Bg# (Nov 25, 2020)

Steel housings have been used successfully in many competition engines. As well as aluminum bearing spacers on the inner races. It's a very complicated application.

Bearing axial clearance is part of the design with the rest of the components to provide acceptable clearance. Production sport (not competition) engines will not be critical of this. In all cases, bearing races must not slip in the housing, thus any axial clearance between outer races and the case is useless.

Theory is fun, but when these parts are made, if the bearings are found to bind upon assembly, a shim can be placed between the front bearing and crank shoulder. This was common practice in many production hobby engines. Recesses to prevent rubbing of the races is standard practice.


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## Ramon (Nov 25, 2020)

dieselpilot said:


> Steel housings have been used successfully in many competition engines. As well as aluminum bearing spacers on the inner races. It's a very complicated application.
> 
> Bearing axial clearance is part of the design with the rest of the components to provide acceptable clearance. Production sport (not competition) engines will not be critical of this. In all cases, bearing races must not slip in the housing, thus any axial clearance between outer races and the case is useless.
> 
> Theory is fun, but when these parts are made, if the bearings are found to bind upon assembly, a shim can be placed between the front bearing and crank shoulder. This was common practice in many production hobby engines. Recesses to prevent rubbing of the races is standard practice.



Hi 'DP' (Greg?)
Are you not meaning radial clearance as I cannot see why axial clearance would allow bearings to slip in their housings.

The effect of adding a shim is no different from having a crankshaft fractionally longer than the make up of the crankcase length between the rear of the front housing and the rear of the rear bearing fully seated.

This is not 'theory' but based on actual application over several builds of diesel engines half of which have been twin ball raced.

I don't dispute that much has beeen done to improve high end engines in high end useage and using superb machines with excellent measuring facilities but perhaps we need to consider something here.

This is trying to help someone who has just finished his first two small engines after quite some difficulty to get them to run. Fired with that success he has picked a design to follow up on what was designed as a racing design circa 1950 and is to be built on basic kit - something we shouldn't overlook, unless, that is, I'm missing something here

Regards - Tug


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## Jasonb (Nov 26, 2020)

I think you hit the nail on the head there Ramon, this is the construction of a *replica* Naylon Viper. If someone wants to use it as a basis for their own modifications then that is another story. With most of them destined for a few bench runs and not likely to be mounted in an airframe any modification are unlikely to reap benifits.

It's a shame a few details were missed off of the drawing, whether that was Eric's measuring or when Ron drew it up. A quick look on Model Engine news will show the OP that there was a raised area for the inner race of the rear bearing to seat against if you look closely at the dismantled original. Also note the reduced diameter between bearings.

An alternative to adding shims as DP suggests would be to make the shaft a little longer and skim a bit off the face that the collet bears against to get the required fit on assembly.


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## Ramon (Nov 26, 2020)

Jasonb said:


> An alternative to adding shims as DP suggests would be to make the shaft a little longer and skim a bit off the face that the collet bears against to get the required fit on assembly.



Well that's exactly what I've been saying from the outset Jason but unless I'm not explaining myself very well it doesn't seem to have come across as such.

I think it would be very fair to say that in the world of home made engines none did those of us who do so better service than Ron Chernich on MEM. His interest in encouraging such has to my mind not been repeated since his passing. I don't know exactly when Ron drew out the Nalon but he was no doubt beginning to feel the effects of his illness. We all know - rather we all _should_ know - that despite the best will in the world those who do drawings will inevitably omit something or, dare it be said, even make a mistake.

The Nalon is a great design - a bar stock engine well ahead of it's time and aimed primarilly for the team racing fraternity. I beleive that it's failure to make a mark was a business decision and nothing to do with the engine itself.

It makes for a very good home build project with, if made well, with a performence to boot no doubt but what it's being made on, what it's being measured with and what the skill of the builder is should always be kept firmly in mind - that is - in my opinion  

Tug


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## pat_pending (Nov 27, 2020)

Hi, and thanks again for the replies. I'll be making some swarf soon i promise so please bear with me as I'm going slow to go fast later (or probably slow by all your standards.

At the risk of doing this one 'to death', below is the CAD now taking into account what I think i've heard above by adding an 0.1mm bit of breathing space behind the front bearing.

The inner race of the front bearing is now drawn tight between the step on the crankshaft shaft and the prop driver/cone and the rear bearing is pressed in tight against the front housing with a little bit of space so the inner race doesn't rub.

The prop should be pulling everything in the correct axial direction but the press fit should stop anything moving anyway. Worst case the bearings move in the wrong direction, 0.1mm should be easily absorbed by the float on the gudgeon pin up-top.

I think I understand it. Sorry of this is all so obvious. Promise some more action soon! 

Patrick


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## Ramon (Nov 27, 2020)

You are getting close Patrick  

Just make sure that the gap behind the rear race inner is nothing more than a scrape - literally a scrape. It needs to just pull the bearing together slightly before coming up tight - too much and you will have the same situation at the other end - crowding the rear race. If you are not sure of getting that right just make the face flat all over. Far better to have a small degree of float in the bearing than crowding it. 

I've been reading the FMV story again - the last time was when it first appeared in Aeromodeller! They do indeed have a spacer as has been previously mentioned but are insistent that the two bearing inners are pulled tight together against that spacer - which brings it all round back to the beginning!

Tug


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## petertha (Nov 27, 2020)

Just a couple of armchair comments to consider

- red arrow, this area looks a little thin for where a lot of forces congregate. Usually commercial 2S engines are quite meaty by comparison and typically even have an array of gussets integrated into the casting. Since you will be turning, might want to give yourself the benefit of more material. It might serve a similar purpose to give the carb throat more material to enter & reside in on the top side.

- green arrow. Usually the back side of the drive washer is flush with the end of the crank housing. Not sure if its for debris mitigation or aesthetics bu it just looks more right. Sometimes the front face of the DW is larger diameter to better fit a specific prop range, but that's up to you. Sometimes you see 2 threaded holes in the front face to use a puller rather than trying to grip on the radius area. Even when the fits are right, oils & such have a way of turning into an effective adhesive over time

- purple arrow. Not sure if this is an aberration of your cross section but the hole should go straight through?


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## mu38&Bg# (Nov 27, 2020)

I had all this typed out yesterday, but dinner and all...

Of course you can design to allow the necessary clearance. The prints do not show this. Once the parts are made and there is a problem, the shim is the easy solution.

The ideal design would result in a specific end play (axial clearance) in the crankshaft at operating temperature. This is what appears to be strived for in competition engines. Theory referred mainly to the idea of attempting to preload bearings in a model engine.

To be honest, I have no idea what crowding refers to. Preload or the races rubbing the housing?

You wrote "_There has to be some clearance behind that front bearing in it's housing otherwise binding will occur_" This is not the case in any production engine I've measured. The outer races are always pressed to the bottom of the bore and interference fit so as not to move at operating temperature. If there is any chance for movement, it will be the rear inner race on the shaft. And there is usually a clearance between the inner race and crank web. Further "_The fit of the front bearing in it's housing is usually of less tolerance ie tightness, than the rear fitting.This allows the bearing slight movement as the shaft expands/contracts with temperature variation_" I have never seen this in production. It may be terminology, I think you are referring to a slip fit of the out race vs the standard interference fit. The Nalon prints say both bearings are a press fit in the case.

In virtually all designs I've seen, both outer races are interference fit to the case, even at temperature and the front inner race is clamped to the shaft. Bearing radial clearance and axial spacing results in some endplay in the shaft. The shaft and case expand at different rates.

A: If the rear inner race is an interference fit, the shaft and bearing axial spacing is such that differential expansion still leaves desired clearance, no trouble. This is a typical race engine setup.

B: If the rear inner race is a clearance fit on the crank and there is room for movement, no trouble. This is typical sport engine setup. This allows looser production tolerance.

Going by the Nalon prints, it's line to line with no clearance between the rear inner race and web. I would add some and allow for a push fit.

I agree that the skill of the builder comes into play, but one can only build to the prints given. Following erroneous prints (regardless of the source), there is truly only one possible outcome. If we assume the skill level doesn't recognize the importance of the bearing assembly, the prints should include it. If we get into how to fix the prints, then there is a lot to be said about the how and why.

I've attached what I will do, eventually. Forgive the awkward prints as I work in metric and this is a clumsy combination of both. So far, I only have the front end drawn and don't know how the rest fits. The crank pin is in the same position as designed and there is plenty of clearance for the rod anyhow. The only other change is the outer races stand 0.2mm proud of the case and the housing flange is thicker.

Eh, sorry for so many words.

Greg


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## Ramon (Nov 27, 2020)

Petertha, 

I was under the impression this was a 'concept' drawing to ascertain the layout as opposed to a drawing to work to but I would agree that as drawn the red arrow area is a little 'thin' and most definitely the tapered hole for the collet should go all the way through the prop driver. There should be a gap however between the prop driver and front of the crankcase - the amount is debatable - too close and debris can be difficult to remove and score the surfaces, too much and debris can find an easy access to the ballrace!

I'm not conversant with larger more modern motors if that is what you are referring to but in all the commercial engines up to 60 size I've handled over far too many years I have yet to see one with holes in the prop driver to assist removal. This is completely new to me. With an ali driver on a brass collet just simple heat will quickly loosen the driver if the taper is not made too fine. As drawn I would say it is possibly on the fine side. I find 25 - 35 * inclusive usually self release with heat quite easily.

Tug


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## Ramon (Nov 27, 2020)

Hi Greg,

I have always understood 'crowding' to be when a ball race is stressed beyond it's running tolerances the balls squeezed by an excess external force, either radial or axial. Perhaps I'm wrong with that terminology.

However in this engine if there is insufficient clearance between the end of the crankshaft and the rear face of the front housing then there is the potential to do just that. Your drawing is much as I have set my own engines up - I just don't see the need to fit a shim when the tolerances can be inbuilt on the shaft.

I agree the the interference fit on both bearings should be correct for the bearing specs however I have always made my engines with a slightly less (outer) tolerance on the front housing to allow for any expansion of the case which allows the case to 'move' over the bearing to suit. As you say the inners are firmly clamped to the shaft - the rear race a tighter fit on the shaft than the front but definitely not clearance. Reading through that FMV story yesterday I note his comment - 'the front bearing should be able to be pushed in with a strong thumb or tapped in with a piece of wood.' I'm sure you would agree that's not the same tolerance that the rear bearing would have and if the tolerance on the shaft was too tight at the front it would probably act to push the bearing out as the shaft was inserted if so fitted.

I don't see any advantage of a crankshaft moving in the rear inner bearing as opposed to having a very small clearance at the front for axial alignment

As I said earlier the Nalon GA prints are 'concept' with no allowances and tolerances.  Any builder has to do as he sees fit with what he is able to achieve and with the equipment at his disposal. Now I agree that the prints should convey the information but despite the best will in the world, mistakes and ommissions not only can or do but will happen. That was certainly the case on the two that I have had published, despite double and triple checking. Incidentally I was also 'questioned' on the ETA's article and drawings by someones perceived inability to work to the tolerances shown for the rear bearing fit! - Both side of the coin!

I know this is a 'racing engine' by design but also as said, one from 1950. If one wants to build it with modern knowledge and incorporating practices developed over years that's one thing but that's a completely different situation from making an engine as an exercise and running on the bench for pleasure - that's another ball game all together. Patrick hasn't made his intent clear on that aspect as yet but given this is ony his third engine I doubt that he has the former in mind.

I'm sure you would agree Greg there's a huge difference for building an engine that has to sustain maximum output over several minutes of a race to that of the average home builder producing something to his own satisfaction that simply 'works' (but works well of course  )

I note your intention to make one (eventually) - I have a 5cc version crankcase done years ago but that's an eventually too 

Regards - Tug


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## mu38&Bg# (Nov 27, 2020)

Let's forget the entire idea of the racing setup as it's far beyond the scope of antique designs and bench running. If you caught the comments about the Nelson design, though vague, imply quite a bit of effort to get the right bearing clearance.

Again, I have never seen (limited to 80's and later) a production model engine with a front bearing that could be pushed in by hand. The latest OS I've had in my hands had rear bearings which dropped onto the crank will the slightest effort. All thrust is taken up by the front bearing, and it's well within spec for load. There are several modern engines which have clamps retaining the front bearing. A floating bearing fit will only get looser with running.

The ability to work to a print is up to the builder. Calling out a press fit without the builder understanding what that maybe is still asking a lot of a builder. Loctite bearing mount is not out of line for bench racing. Looking at tenths or micron callouts on a print may look scary, but with some practice and technique not impossible.

We do essentially agree. 

I didn't have the Viper prints in my library until I posted on Wednesday and found them on Adrian's page. The same page showed the Russian VIKHR 2.47. The tidbit about CAD and having a go at prints caught my eye. The model is 90% complete and prints will follow. It turns out the drawings presented in the Gajewski book for this engine are also conceptual, with errors and lack of clearance. Some others in this book were fully toleranced. The bearing arrangement intended is unknown, probably both bearings slip fit over the crank. I also wonder how the piston was made. I'll probably do an as designed backend and one slightly altered for easier home building.

Oh, I love your 5cc builds. I'd be more inclined to attempt some in 0.5cc myself.


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## Jasonb (Nov 28, 2020)

regarding the red arrowed area, Ron's drawing show it differently with the concave waist blending into the front flange, this can also be seen on the photo of the original I posted earlier so a modification to the 3D model will not only allow this to be thickened up but remove the sharp internal corner that could be a stress raiser.

I've not see the thrust washers Peter mentions on any of the older engines only on newer ones, maybe due to the more recent use of electric starters pushing the front end back into the bearing which you don't get when hand starting combined with the use of "D" shaped drive for the prop driver and not a collet..


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## Ramon (Nov 28, 2020)

Hello Greg,

Well I've stripped quite a few engines over time but don't ever recall any rear bearings with what I would deem a loose fit on the shaft.  Doesn't mean I disagree with you just I can't recall having witnessed it. To me though to have the shaft 'loose' in the rear bearing seems to defeat the object. Agreed though the fit must be such that it only just grips and not a force fit.

I noticed the comments on Henry Nelson method in the FMV story - particularly that he had (to them) an excessive interference fit on the rear outer bearing to cope with radial expansion but that he fitted races with very high clearance - something which they (Metkemeyers) state were difficult to source unless made in large orders.

Looking at the VIKHR drawing the set up is quite different in that the prop driver is not seating on the bearing so the bearings are held purely by their interference in their housings. I don't quite understand those two small areas behind the inners though. Does that represent a gap or is that an insert?

As we both agree though, an engine set up for the kind of performance required for competitive racing is a very different matter.

Yes the person who questioned the tolerances felt exactly as you infer. But the ability for the home builder to achieve it without recourse to grinding precision is there with careful application.

Lot's of Ron's drawings (and my own) feature line to line GA but the parts drawings should have the tolerances/allowances drawn. Even then things get left out. I checked my Oliver Tiger drawings - no dimension shown on the crankcase for the distance between bearing housings (it can be interpolated though) The crankshaft however does show an increase of 0.1mm over that build up.

.5cc ???  Ha no way.  I'll give that a miss - far too small for my liking but I am thinking about coming down by half

Jason - Peter, the only engine that I can think of that has a thrust washer behind the prop driver are the OS 35 engines but they are plain bearing.

I really hope we haven't spoilt your thread with all this Patrick we really ought to hand it back over and see what you've been up to  

Regards  - Tug


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## pat_pending (Nov 28, 2020)

petertha said:


> Just a couple of armchair comments to consider
> 
> - red arrow, this area looks a little thin for where a lot of forces congregate. Usually commercial 2S engines are quite meaty by comparison and typically even have an array of gussets integrated into the casting. Since you will be turning, might want to give yourself the benefit of more material. It might serve a similar purpose to give the carb throat more material to enter & reside in on the top side.
> 
> ...





petertha said:


> Just a couple of armchair comments to consider
> 
> - red arrow, this area looks a little thin for where a lot of forces congregate. Usually commercial 2S engines are quite meaty by comparison and typically even have an array of gussets integrated into the casting. Since you will be turning, might want to give yourself the benefit of more material. It might serve a similar purpose to give the carb throat more material to enter & reside in on the top side.
> 
> ...





Ramon said:


> Hello Greg,
> 
> Well I've stripped quite a few engines over time but don't ever recall any rear bearings with what I would deem a loose fit on the shaft.  Doesn't mean I disagree with you just I can't recall having witnessed it. To me though to have the shaft 'loose' in the rear bearing seems to defeat the object. Agreed though the fit must be such that it only just grips and not a force fit.
> 
> ...


Not at all. I'm just taking a while to digest it all!


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## pat_pending (Nov 28, 2020)

petertha said:


> Just a couple of armchair comments to consider
> 
> - red arrow, this area looks a little thin for where a lot of forces congregate. Usually commercial 2S engines are quite meaty by comparison and typically even have an array of gussets integrated into the casting. Since you will be turning, might want to give yourself the benefit of more material. It might serve a similar purpose to give the carb throat more material to enter & reside in on the top side.
> 
> ...


Thanks. Armchair comments v welcome.  Yes the Hole will go straight through. This was sloppy CAD work on my part as I'm a Fusion360 novice. Also the driver will be as flush against the front bearing as I can get it. RE that 'red corner' i will chamfer so theres a 2mm additional material there.


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## petertha (Nov 28, 2020)

Ramon said:


> Petertha,
> I'm not conversant with larger more modern motors if that is what you are referring to but in all the commercial engines up to 60 size I've handled over far too many years I have yet to see one with holes in the prop driver to assist removal. This is completely new to me. With an ali driver on a brass collet just simple heat will quickly loosen the driver if the taper is not made too fine. As drawn I would say it is possibly on the fine side. I find 25 - 35 * inclusive usually self release with heat quite easily.



You're right, it isn't common. The only ones I've seen are on larger displacement engines or retrofitted on known problematic engines. And of course now that I'm looking for pictures, they seem rarer yet! LOL. I might be thinking of bigger displacement or non-collet, straight bore & keyed? But if you Google 'rc drive washer removal' you will get the range of gadgets & how-to articles, so I think I can safely say 'stuck' is not completely uncommon on the smaller 2S engines. The vast majority have the same standard parts layout - split tapered collet that mates the drive washer with the same taper angle.

And I agree with you 100%. For the common small displacement, heat 'should' release even the most stubborn parts purely via the taper angle & higher thermal expansion of aluminum vs brass collet & steel CS. Whether its related to (over) prop tightening, swapping props when engine is still warm, heat/cool distortion, the miracle of castor oil metamorphosis into the worlds strongest glue... I've experienced this many times myself. I try to use torch heat sparingly, but the fun begins when you try to get the puller jaws onto some uncooperative feature of the drive washer without scraping up the material. So the threaded holes is more of a retrofit suggestion for people like us who have the tooling & capability. The holes are completely hidden behind the prop hub & may never get used but are there for insurance. My radial has the same split collet arrangement but there is an array of threaded holes in the drive washer for the prop/washer so I can utilize those if necessary.

Sorry to impose on the post, like I say just armchair comments.


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## Jasonb (Nov 29, 2020)

The one in your first picture is not a even a collet type, it has a flat on the crankshaft and "D" shaped hole in the driver so could be overtightening or its been on there a long time.


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## Ramon (Nov 29, 2020)

Peter - Next to bad deformation marks on screw on cylinder heads where the wrong tool has been used for removal I don't think there is anything worse that offends my eye as much as seeing plier teeth marks on a prop driver !! Most collet types will ease with heat - I use a heat gun as opposed to a torch - but some just won't budge so I'm with you all the way using a puller. As I thought, it seems then the holes 'for the use of' are in much larger engines than I have handled.

The worst type of driver fittting in my view is the straight knurled shaft - the driver 'graunched' on and a devil to remove without loss of tightness when refitting.

Only engines I know with a flat on the shaft Jason are OS - that's not an OS in Peters image I recognise straight off - are there other manufacturers using that method? Thunder Tiger perhaps

Greg - Had some real problems at first but finally managed to get on Adrians site - fully up to date with the VIKHR 

Just found some still sealed Hoffman bearings too 

Tug


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## petertha (Nov 29, 2020)

Jasonb said:


> The one in your first picture is not a even a collet type, it has a flat on the crankshaft and "D" shaped hole in the driver so could be overtightening or its been on there a long time.



You're right, I didn't look close enough. Was just referencing yet another jerry-rig puller pic, of which there are many.
OK probably beat this issue to death. Good luck with the build.


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## pat_pending (Dec 6, 2020)

Hi everyone, just a quick update. Not had a huge amount of shed time recently as I have been really busy at work. Every evening I think I'll give it a go but when the time comes, my brain just seems so fried that I'm worried I'll just fill the scrap bucket or worse still, have an accident. I have two weeks off over Christmas and really exited to carve out some quality time then.

Anyway, I've got going now. No turning back!

So this weekend I squared up some stock and started making plug gauges for the crank case and the cylinder bore. Still the gauges for the bearing seats and the cylinder heatsink to go. I used EN1A PB steel for these and it seems to work OK and get a decent shiny finish with a light finishing cut of 0.05mm or so at 1000RPM.

Squaring the stock is something that took me FAAAAAR too long (frustrating). I've only done it once before and really there are just so may things to get you out of whack. With a bit of patience and 8 machining operations per block (6 plus two to measure and mill to final size) I got there. A couple of thou under dimension on one of the blocks in the horizontal direction but this will be this will just be the mounting screw lugs so I'm not worried.

One thing which I figured out (no idea if this is silly or not) is Iremoving 2 of the cutters from a 3 cutter cheepo indexable face mill to use it as a flycutter gave me a lot more accuracy on setting the z-axis. One cutting tip was a lot easier to set accurately (with a thin cigarette paper Rizla blue). This seemed repeatable to 0.01mm ish. I wasn't in a hurry so took light cuts at 0.1mm and the vibration from the single cutting tip and interrupted cut didn't seem to be a problem

The front of the crank case and the top were left about 0.5mm oversize in order to be able to skim the face on the lathe before boring to make absolutely sure everything is perpendicular.

Next operations are to mark out everything, finish making plug gauges and then the fun starts.

I'm thinking it makes sense to drill/tap the cylinder head and crank case front housing mounting screw holes while I'm at it. Rationale is that If I do everything from a single setup/datum surface, there is less opportunity for errors to cascade. The other alternative is to make a PCD drill jig to fit into the crank-case openings later. I would be interested to hear people's thoughts on this. I got lucky on the BollAero and the holes lined-up OK but always on the lookout for tips n' tricks / better ways of doing things.

Anyway, please enjoy the most boring model engineering photos you've seen all week . It will pick up pace soon promise!

Patrick


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## Ramon (Dec 6, 2020)

A good start Patrick 

Given that you are making two a drill jig that could fit both case bore and front and back housings would be a well considered way to ensure compatability. Second option would be to wait until after the bores are done then do them on the mill using co-ordinates - much more reliable from a positioning point of view than marking out.

Good to see you making swarf on this   

Regards - Tug


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## pat_pending (Jan 31, 2021)

Hi All, after a few weeks of fettling with my machines etc ( fixed and re-fitted the DRO kit I had gathering dust) Im back in business! Managed to get some quality 'shed time' this weekend and started making some swarf. Amazing how minutes, hours, days all blur into one when you get truly heads down. I have some making up to do with the family who might have got an hour with me tops.

Anyway, I managed to turn those two blocks of ali into a pair of crank cases. this is the journey.

First up. Marked out to remind me where what was and centres set using the DRO on the Mill. The stock was left 0.5mm oversize on two dimensions to allow me to take a skim on the lathe before boring.






Next up used the 'wiggler' to set the stock up in the 4-jaw running true to the spot drill marks from the previous step.







Now first up, take an 0.5mm skim off the stock mounted in the chuck to make sure the hole is perfectly perpendicular. I really need to experiment with using the lathe faceplate. It came with my SC6 and I have never used it since I got it 7 years ago. Suspect that would open up a world of alternative work-holding. One to try.







Now I spotted again and drilled progressively larger holes up to 16mm where the boring bar fitted with ease. Now boring to make as decent a surface finish as possible on the final passes: This thing needs to be airtight!







Now time to flip over and repeat the procedure for the top of the crank case.







The finished intermediate articles. From here on in, everything is referenced relative to the bores. The external dimensions I figured were cosmetic more or less. The Important measurements are vs the crank case bores.







Using the new toy I got for Christmas this year to locate everything nicely on the mill. No idea how I survived without one of these!.







Milling, milling, more milling... and then some more..






After several operations. Thought I would get the tapping drill holes done while in this setup.







Flip 45deg to get the chamfer. Not super happy with the result as I have a small ridge left over at the edge. It was very hard to set up the position of the cutter here and relied on 'by eye' perhaps a bit too much.


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## pat_pending (Jan 31, 2021)

And flip it over to mill the bottom:







Now drilling and tapping for what seemed like a whole day. No broken taps today which is a first and very lucky given the amount at stake with each of the crank cases!






The hardest part for me was to figure out how to do the 5mm round bit near the top of the crank. I thought the best would be to make a simple mandrel. The eternal dimension again was 'cosmetic' so it didn't have to run 100% true. I used the taper tap method I've used for laps before. The stock was a bit too thick for it to expand easily but it seemed to grip firm enough with the odd slip here ad there.








The first attempt was to mount the mandrel in the lathe and use a parting blade to cut the recess. The process aged me about 10 years! interrupted cut, crank case that i'd already invested 10 hours + into held by the flimsy mandrel. Chatter! lets just say I won't  be trying that again!!







So in the end i went for a plan 'B' on the second case and used the rotary table instead. Milling with a 2-flute endmill and 0.2mm at a time turned out to work a lot better and cause less stress to both myself and the part. I think this is the way ill do it next time although it was very slow.







After everything else was done, I tapped the tops of the crank cases using a tapping fixture and a 'floating' vice arrangement. 







Right. I've been going on about this for long enough! Here they are. I'm happy enough and happier sill i didn't destroy anything with a silly mistake at the final stage. Surface finish leaves a lot to be desired but i think tweaking feeds-speeds etc will be one for next time. I think the spindle bearing on my SX3 has seen better days too. I'm sure that can't help matters.







Anyway. Thanks for looking. That's all for today. Next stage I think will be turning this bolt into a pair of crankshafts.


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## Jasonb (Feb 1, 2021)

Good to see you back onto these and they are taking shape quickly..

For when you start the next engine project the reduced diameter below the flange could have been done while the block was in the 4-jaw for boring the hole removing as much as possible with a turning tool then swapping to the parting tool once down to max dia across the flange. Talking of turning as you seem to like insert tools treat yourself to a couple of half decent CCGT inserts with a 0.2 tip radius and add a drop of paraffin to the work and you will get a very good finish.

As for the milling first check that the backlash of the bearings is adjusted OK and then look at your milling cutters and cutting methods as you should be producing nice chips not crumbs.


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## pat_pending (Feb 1, 2021)

Jasonb said:


> Good to see you back onto these and they are taking shape quickly..
> 
> For when you start the next engine project the reduced diameter below the flange could have been done while the block was in the 4-jaw for boring the hole removing as much as possible with a turning tool then swapping to the parting tool once down to max dia across the flange. Talking of turning as you seem to like insert tools treat yourself to a couple of half decent CCGT inserts with a 0.2 tip radius and add a drop of paraffin to the work and you will get a very good finish.
> 
> As for the milling first check that the backlash of the bearings is adjusted OK and then look at your milling cutters and cutting methods as you should be producing nice chips not crumbs.


Thanks Jason, ill have a go with the CCGT inserts. I've been meaning to disassemble the head on the mill for a while now as its a bit noisy but been putting it off! I think that's the next project after these two engines are off the workbench. Patrick


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## Ramon (Feb 1, 2021)

Hi Patrick, Yes good to see you back on this again.

Re the mandrel. You will get a far better grip if you put four cuts in rather than two. Secondly it's best if the cuts do not go past the work piece. I always turn the mandrel over size then tap and deeply centre before cutting - the actual expanding bit does not need to be very long so I relieve the mounting part using a parting tool. Remove and cut to the depth of the relieved area then replace in lathe - clean the thread and centre. Put in the expanding screw till it just touches and turn the OD to the diameter required. It is not a good idea to make mandrels for ali parts from aluminium due to the risk of galling. If it does and it's potentially likely too, you wont get it off the mandrel without damage occurring.

I turn a 60* angle on caphead screws for the expander - usually 2BAor 5MM or so but to suit the size of mandrel.

Looking forwards to further progress - I'll reply to your PM later

Tug


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## pat_pending (Feb 1, 2021)

pat_pending said:


> Thanks Jason, ill have a go with the CCGT inserts. I've been meaning to disassemble the head on the mill for a while now as its a bit noisy but been putting it off! I think that's the next project after these two engines are off the workbench. Patrick


Just double-checking, those **are** the inserts I used in the end for the boring which turned out really nice (the grey/silver ones). I bought them from Glanze a few years back but havent had a chance to use. Ill stick them in the left-hand tool also for the future turning ops. Seems to make a difference.


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## Jasonb (Feb 1, 2021)

The bright ones are what you want. Good on aluminium, brass bronze etc and can also be used for fine finishing cuts on steel and stainless. In your first picture facing off the block you can see the surface is picking up a bit which you should not get with the CCGT and a bit of paraffin or WD40.

This sort of tip Pack of 2 CCGT 060202 ALU AK10 Carbide Tips


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## pat_pending (Feb 1, 2021)

Jasonb said:


> The bright ones are what you want. Good on aluminium, brass bronze etc and can also be used for fine finishing cuts on steel and stainless. In your first picture facing off the block you can see the surface is picking up a bit which you should not get with the CCGT and a bit of paraffin or WD40.
> 
> This sort of tip Pack of 2 CCGT 060202 ALU AK10 Carbide Tips


Just ordered a few to give them a try + have my paraffin on standby.


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## pat_pending (Feb 2, 2021)

Ramon said:


> Hi Patrick, Yes good to see you back on this again.
> 
> Re the mandrel. You will get a far better grip if you put four cuts in rather than two. Secondly it's best if the cuts do not go past the work piece. I always turn the mandrel over size then tap and deeply centre before cutting - the actual expanding bit does not need to be very long so I relieve the mounting part using a parting tool. Remove and cut to the depth of the relieved area then replace in lathe - clean the thread and centre. Put in the expanding screw till it just touches and turn the OD to the diameter required. It is not a good idea to make mandrels for ali parts from aluminium due to the risk of galling. If it does and it's potentially likely too, you wont get it off the mandrel without damage occurring.
> 
> ...


Thanks Tug. Ill give that a go. Good tip on the different metals. Currently setting my mental energy to figuring how to machine a 'crescent' style counterweight in the crank web as per the plans. Re-reading your ETA thread for some tis n tricks as usual  .


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## Jasonb (Feb 2, 2021)

If you bore a hole in a scrap block of metal and add a couple of grub screws from the side to clamp the crankshaft and then it's easy to offset the block in the 4-jaw to do the pin hole or turn the pin followed by the crescent. Put a bit of soft aluminium in the grub screw holes first then they won't mark the shaft. Now I Have collet blocks I would possibly hold in that then block in the 4-jaw or a Keats angle plate would do the job too.


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## pat_pending (Feb 2, 2021)

Jasonb said:


> If you bore a hole in a scrap block of metal and add a couple of grub screws from the side to clamp the crankshaft and then it's easy to offset the block in the 4-jaw to do the pin hole or turn the pin followed by the crescent. Put a bit of soft aluminium in the grub screw holes first then they won't mark the shaft. Now I Have collet blocks I would possibly hold in that then block in the 4-jaw or a Keats angle plate would do the job too.


Thanks again Jason! On the last engine I used a piece of round stock with the offset precisely drilled and the shaft bolted through per below. Worked well but I guess you can get much more precise with a 4-jaw (also use to do the counterweight as you show + can re-use the fixture rather than one per engine). I cannot see the the cutting tool you are using very well. Do you happen to have any more detail you could share?


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## Jasonb (Feb 2, 2021)

IT's just a 3/16" HSS toolbit ground with a round nose and a good amount of clearance so it does not run on the concave surface


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## Ramon (Feb 3, 2021)

Hi Pat, 

I'm not keen on using a block to hold in the four jaw for a couple of reasons. Even with careful set up there is no 'absolute guarantee' that the shaft is co axial so the pin could, might, be off to the shaft. However slight that is not a good thing to have. Obviously it would have far less effect on turning a scallop out but it's worth pointing out. Secondly with drilling a block and holding with screws it's dedicated block - both in diameter and in offset (throw) for that particular op.

Depends on if you are intending to make other engines but something on the lines of this is far better






This is infinitely variable within its range, holds a shaft exactly coaxial and of varying diameters. It does not mark the shaft when holding either and can of course hold a finished shaft without any chance of marking the finished surface.  I rough the pin first as above, finish the shaft diameter between centres then finish the pin similar to the image. Every thing in line and you have the fixture for the next engine.

I happen to have a spare piece of the cast angle used - yours if you want it, just let me know

Tug


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## pat_pending (Feb 3, 2021)

Thanks for the reply as always Tug! I will have a go at using your method and indeed a piece of the angle cast iron would be very useful.

A couple of questions if I may:

1) I assume you machine a 'V' in the cast angle in order to seat the shaft?

2) I saw from the ETA build that you rough out the pin square first on the mill and then take it to the lathe for these operations. What is the rationale there? Just a less violent machining operation than removing all that material as an interrupted cut on the lathe/risk of distorting something or disturbing the fixture?

3) In terms of the order of build I assume you would do the conrods before the crankshaft so you can fine-tune the fit on the crank-pin?

4) How do you go about polishing the crank journals? Just a bit of fine emery paper/wd40 and a flat edge?

There were a couple of things on the Viper design that I'm tempted to change. 1) Domed piston and contra. Added complexity potentially negligible running benefit. May make one of each to compare however there are so many other variables here that this wont be particularly useful comparison. (2) The integral threaded shaft rather than using a high-tensile bolt at the end as I think the work holding will be easier and more rigid if I only need to hold the 'thicker parts' of the shaft as per your pictures. Shouldn't cause too much uproar from the purists I would think.

I'm really chuffed with the crank cases so far (all relative to my previous accomplishments but obviously have years of practice to get to your standards  ). Looking forward to moving on to the next stage.

Thanks,

Patrick


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## Ramon (Feb 3, 2021)

Hello Patrick,

In answer .....

1, Yes best if done with a 45* cutter having gashed the slot with an endmill to relieve the bottom. Do the groove and clamp first. Turn a piece of steel to a parallel dimension (no taper) and clamp the part to it then face the bolting face with very light cuts. This will ensure squareness of shaft to the lathe axis in both planes.

2, Yes again, I find there is far less stress on the part than interrupted cuts on the lathe especially if using tough steel such as En24T.

3, No I usually do the rods towards the end of the build - just make sure the pin is on top tolerance to allow for that last bit of finishing

4, I use wet and dry carborundum paper either free hand for small sections eg under a bearing or stuck to a flat parallel with double sided tape and plenty of paraffin and oil as a lube (approx 90:10 ratio paraffin to oil) for wider areas.

I must admit I've never seen an engine with a piston design as drawn. If you do change things make sure the top edge of the piston remains at the same place. A straight cone and much more obtuse would be acceptable on both piston and contra

PM me your address and I'll sort a bit of cast out for you.

Regards - Tug


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## petertha (Feb 3, 2021)

Ramon said:


> Re the mandrel. You will get a far better grip if you put four cuts in rather than two.
> I turn a 60* angle on caphead screws for the expander - usually 2BAor 5MM or so but to suit the size of mandrel.



Ramon, what is your preferred method to make the slits?
I've put my part in a square collet block & used the bandsaw along a makeshift fence. Its rarely exactly down the center, but I haven't been able to determine if it ultimately makes a lot of difference if doing the finish OD turn prior to mating the part anyways. Slitting saw sounds like a better plan but its a long messy process & probably not feasible on longer parts anyways.

So you turn the head of a capscrew to 60-deg primarily to match taper of 60-deg of center center drill?

I've seen other references to pipe threads (tapered threads?) but I've never quite understood this. If the head is snugged before final OD cutting & the fit is say 0.001" undersize, then its just the expanding squeeze that's doing the  internal clamping right?

Have you ever tried any of those expand ID collar sets? Aside from 'yet another tooling set' its more like an ER collet principle with alternating slits on either end so theoretically a more unified diameter change over length. I bought a single size offshore model. The grip wasn't bad but I wasn't happy with the runout even supported between its centers. Maybe got a Monday model but kind of cooled my jets.


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## Ramon (Feb 4, 2021)

Hello Peterha

I always cut the slits with a standard hacksaw (or a junior one if very small - I have made them as small as 1/8 diameter but just the one slot in that case) On a couple of larger diameter ones made I cut three slots but most at two at 90 degrees by eye.

I was shown this tip many many years ago and the person who passed it to me turned the 60 degrees on a caphead so I've done it ever since. Some use a standard countersunk screw but though it works the angle is too obtuse in my view - the 60 degrees allows a very secure grip with little torque on the screw. I've done this as small as 8BA and the largest has been 8mm. 

Some time back I bought a very nice set of mandrels at a show. Well made and very nicely finished - I've never used them! - mainly because they never seem to match in diameter to the work piece. They are so easy to make oneself, obviously the thread needs clearing out after slitting and once turned to required diameter hold a work piece extremely well and are always as accurate as the lathe itself.

I very rarely reuse a mandrel a second time for it's given turned diameter but recycle them downwards re-turning to new use each time.  I roughed out quite a few  from bar ends when at work but am now finally on the last one

Hope that's of use Peter

Ramon (Tug)


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## mu38&Bg# (Feb 4, 2021)

The idea is to be as close as you can in size, so that expanding the mandrel only adds pressure, not distortion. In this case a small offset of the slots shouldn't matter. If the mandrel has to bend to make contact with the part, we would expect non uniform segments to bend unequally as well as make point contact on the part. Preloading the arbor prior to cutting (to allow some retraction) is typical to assist in removal of the parts and allow for some tolerance (if you've looking at expanding 5C collets for instance). When engagement length is short, clearance isn't really an issue, but tolerance may still be a concern if making many parts.


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## Ramon (Feb 4, 2021)

Agreed - if you are making your own the expanding area needs only to be sufficient to provide the grip. The rest of the mandrel should be as close a tolerance as you can get and particularly so when doing the front bearing housings either on a case or a separate crankcase front - the plain part provides the location - the expanding part the drive. I've never felt the need to expand the mandrel slightly before final turning just bringing the screw up until it touches is sufficient.

If the mandrel is going to be used for support when porting is drilled or milled through a liner for instance, due clearance needs to be milled into the mandrel to allow for any burrs created as the part is removed from the mandrel.

Tug


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## pat_pending (Feb 15, 2021)

Hi all,

I managed to get a bit of shed time this weekend so thought I'd share progress. I tackled the crankshafts and, after a few 100g of additional weight added to my scrap box, I'm pretty happy with the end result. Thanks for all the previous suggestion on this thread which helped a great deal. I picked out the tips and tricks that matched my skills and tooling.

Having run out of high-tensile bolts (my usual go-to for crankshaft steel stock) I ended up buying some EN24T off eBay and must say it made such a difference. Easier to machine, less showers of red-hot metal burning my arms when trying to machine away the threads and probably healthier as Im not sure breathing in vaporised galv coating is such a good idea! Anyways, I'm a convert.












I made one according to the plans which stated cutting out a crescent in the web as counterweight. After doing this I checked and the counterweight specified didn't even cancel out the wight of the crank pin let alone any attached piston and conrod. In the end i decided to make the second crank with a simple cutaway, This seems to counter the weight of the pin much better. We will see if it makes a difference in the running engines.

So heres how I made em..







Turn down to 1mm oversize (11mm) with a lice centre and thread the final bit M6.




Stick in mill and mark out the crank throw using DRO.






Mount in a piece of aluminium faced and reamed hole for the oversized crank journal.






use a wiggler to locate on the crank pin.






Tun the crank pin and polish for fit into reamed 5mm hole.






Cut away the crank web counterbalance.






Finish between centres and polish for a firm push fit for the bearings. This is suck a nifty way of doing it as you can take the crank out by simply moving the tailstock, checking bearing fit, slapping back in. Saves a load of time and ensures its running true. Thanks to Jason and Tug for the tip.

The 10 picture limit makes 3 solid days in the workshop seem unimpressive but I reckon I have some cranks that will do the job v nicely. Next up, I'll try to turn my attention to the front housing and conrods.

Thanks,

Patrick


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## pat_pending (Feb 16, 2021)

And on the topic of crank web cut-outs, i was wondering what people's 'go-to' method for doing them is. This is my first time attempting it so I spent a good bit of time reading the piece on modelenginenews which details a number of different approaches.





__





						How To Machine Crankshafts
					





					modelenginenews.org
				




I went with what I thought was the simplest. Firstly do a quick sketch on Fusion360:






From this i figured out how high the pin needed to be held above the vice if the crank journal was resting on the top face.






Mill the top. Flip round to the other side and do exactly the same depth from there.











This is the result pre finishing between centres and polishing etc. Most importantly the counterweight compensates the crank pin (which it didn't seem to using the crescent specified in the plans. Perhaps i didn't remove enough material.).


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## methuselah1 (Feb 16, 2021)

pat_pending said:


> And on the topic of crank web cut-outs, i was wondering what people's 'go-to' method for doing them is. This is my first time attempting it so I spent a good bit of time reading the piece on modelenginenews which details a number of different approaches.
> 
> 
> 
> ...


You know, I''d dearly like to make one of these, and others, but although I'd have gladly paid for the Motor Boys' disc, unfortunately I only discovered M.E.N. after Ron had died, so there was no-one TO pay.

I have enjoyed great support from this group; Gail Graham came to my rescue with "the book" (as well as help with my "Lobo Pup") never mind Les Stone's help with an FTPT and other, very kind members; I am at a loss as to how to obtain the disc designs. Would the remaining Motor Boys allow limited distribution? Does anyone have one to sell? Please help- I cannot be the only one in this situation!

-Andrew Curl (UK)


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## IanN (Feb 16, 2021)

pat_pending said:


> And on the topic of crank web cut-outs, i was wondering what people's 'go-to' method for doing them is.
> :



Hi Patrick,

Once you have dimensioned drawings to work from, my preferred method is to:

1) Mark out the two lines on the crank web

2) Hacksaw along lines

3) Tidy with a file

All the best,
Ian


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## Jasonb (Feb 16, 2021)

Andrew if you want the Viper drawings they can be found on Adrian's web site, link at the bottom of this page


			https://adriansmodelaeroengines.com/catalog/product.php?cat_id=33&pid=155


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## Ramon (Feb 16, 2021)

Andrew 

A link to the book (disc) designs for free down load are actually on here courtesy of Ken Croft, one of the engine boys.

A quick google found this Go to RCLibrary : Motor Boys International Model Engine Plan Book title : download free vintage model aircraft title

That should help 

Pat - there are several ways of relieving the crank web - don't know if you saw this on here
Super Tigre G32 1cc diesel - a 5cc version

Scroll down about halfway on page five and into page 6

Ramon (Tug)


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## methuselah1 (Feb 17, 2021)

Jasonb, Ramon, thank you!


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## pat_pending (Feb 20, 2021)

Hi all, I managed to get a few hours in the shed this week and got the front housings done for both engines. I'm pretty happy with the result. Making 2 engines I have ended up putting all my 'first try' pieces on one and all the better bits on engine 2. Still both looking OK. Something I'm not entirely happy with is the matching of the shape of the chamfers to those of the crank case. I think there must be a better way of doing it e.g making a larger bit of aluminium in one piece and then machining crank case, housing and back plate from them thus guaranteeing the mating shape (provided all the other operations are accurate. One to try for the next engine.

Bit of a tidy-up in the workshop then I reckon I'll have a pop at making some conrods.

Thanks,
Patrick






Bolted together and the holes matched PERFECTLY  . I think centering the mill on the bore and measuring from there seems to work much better than my previous attempts of measuring from an edge. Thanks Tug for the tip.







First I squared the stock and made some plug gauges (approx .025mm under size vs. the bearings).







I went for a test fit in a piece of scrap aluminium before risking anything on a machined part. The rear bearing slid in really easily when the test piece was heated to about 250c with the heat gun (not too sure the temperature gauge on those is that acurate tho  ). Once cooled, the bearing seemed to rotate nicely without any rub etc so I decided to go ahead with this fit.






Next i centre marked the aluminium blanks on the mill using the DRO and centred it on the 4jaw in the lathe.






Next the rear bearing seat was bored and the through hole reamed.






Next the part was rotated and centred using the indicator on the hole. Crossing my fingers this will be accurate enough. We will see. The front bearing seat was then bored. Next up I made a fixture to hold the par for profiling.






Then profiled the front housing outers:


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## Ramon (Feb 20, 2021)

Good progress Patrick but if you get the front and rear bearing in line concentrically and parallel with each other on a four jaw set up you will be a lucky. I'm not saying it can't be done but there is no way of knowing exactly where the rear housing is in a four jaw set up. For the tolerances required for a twin bearing front end it does have to be exact. The crankshaft with rear bearing in place should slide straight in to the front bearing once fitted. Does not have to be out by much to introduce running issues.

Much better to fit the part to an expanding mandrel made to a good fit in the rear bearing housing and expanding in the shaft hole for grip. Done all my engines like that and not had misalignment.

Hope you are lucky though - fingers crossed for you

Tug


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## pat_pending (Feb 20, 2021)

Ramon said:


> Good progress Patrick but if you get the front and rear bearing in line concentrically and parallel with each other on a four jaw set up you will be a lucky. I'm not saying it can't be done but there is no way of knowing exactly where the rear housing is in a four jaw set up. For the tolerances required for a twin bearing front end it does have to be exact. The crankshaft with rear bearing in place should slide straight in to the front bearing once fitted. Does not have to be out by much to introduce running issues.
> 
> Much better to fit the part to an expanding mandrel made to a good fit in the rear bearing housing and expanding in the shaft hole for grip. Done all my engines like that and not had misalignment.
> 
> ...


Bugger. Wish I'd thought of that and makes sense now you mention it. Ill try and do a test fit tomorrow. 10hrs work potentially in the scrap bin.... i guess thats how you learn + makes the end result that much more satisfying.  

P


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## Ramon (Feb 20, 2021)

Well it's not as bad as you might think Patrick and yes you can learn from it - not only the mistake but how to rectify it.

Fit the front bearing and try the shaft and rear bearing - if theres any form of misalignment don't force it just remove the bearings. Turn a ring of ally say .5mm bigger than the front housing diameter with an inner diameter smaller than the bearing intended

Make a mandrel as suggested and hold the front housing by it then bore out the front bearing housing to take the ring - Loctite that in place then turn to finish size. If you use a retaining compound and you get the fits right you should be able to turn the inner surface within 20 mins or so.
Not ideal on a new build but It works - reclaimed several  commercial engines doing this - both front and rear bearings.

Give it a go - you've nothing to lose  

Tug


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## Peter Twissell (Feb 20, 2021)

Re. Alignment of chamfers, I will either machine the chamfers on the parts after they are otherwise finished and bolted together, or make the chamfers on the end parts a bit smaller than those on the crankcase, so there is a clear intentional difference.


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## pat_pending (Feb 21, 2021)

OK, so it seems lucky on one front housing and the other seems tight when i insert the shaft into the bearings. Close but no cigar.

I will put the working front housing on my #1 engine (with all the other iffy bits) and try to make the other one perfectly using an expanding mandrel.

Now if only squaring a piece of stock to size before i even get to machining wouldn't take me an hour!


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## Ramon (Feb 21, 2021)

Morning Patrick, now off for a day in the garden for a change but before I go ........

The mandrel wants to fit the rear bearing housing as a plug gauge would - the front portion of the gauge is the part that does the gripping - a 2 BA/4mm cap head would be fine for the expanding screw. The part is pushed fully back to seat against the front face of the mandrel










I prefer this way as all machining is done with reference to the rear bearing housing itself.

It can be done by holding the outer diameter of the rear bearing housing in a clamp plate bolted to the faceplate but again you are not referencing the bearing housing directly.  The mandrel method is as good as your lathe is and the fit of the part to the major diameter. Once it's out of the lathe it can only be used (to the same degree of accuracy) for some thing smaller

I should add it's important that the rear housing and shaft clearance in the part are done from the same end and at the same time

Hope that helps some - Tug


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## pat_pending (Feb 21, 2021)

Thanks Tug.Those pics are very helpful. Will get making one asap.


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## Ramon (Feb 21, 2021)

This might be of use to others Pat so repeating it here.

Hi Pat - just come in for a coffee!

Make the ring first, say .5 mm larger than the housing and about 2mm wall thickness, face one end square to the bore and chamfer the outer diameter. Set the part on the mandrel and bore until the ring slips in easily - about .03/.05 larger than the ring - no more. Do this gingerly as you do not want to have the two surfaces gall. Use the 638 and Loctite both parts. Hold the ring against the front face of the tailstock drill chuck and use that to push the ring in square and to the bottom. Don't go for a tighter interference - the Loctite could go off before you are fully home and you do not want to use force in any way in case you disturb the mandrel. Let it cure for a bit - if the fit is as above it should be machinable within 20/30 mins but no sooner. Take very light cuts and take a very fine final cut off the rear face to ensure it's square. I wouldn't fit the bearing for 24 hours so the Loctite can really cure

Despite what it says on the product information Loctite has a very long shelf life so if it doesn't go off you've got too big a gap!

Good luck - Tug


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## KenC (Feb 21, 2021)

pat_pending said:


> OK, so it seems lucky on one front housing and the other seems tight when i insert the shaft into the bearings. Close but no cigar.
> 
> I will put the working front housing on my #1 engine (with all the other iffy bits) and try to make the other one perfectly using an expanding mandrel.
> 
> ...


Have you seen the video by Joe Pie... on squaring blocks on the mill. 
I found it helpful and I always do it this way.
Ken


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## Ramon (Feb 21, 2021)

Excellent link Ken, I do climb mill to eliminate burs but it does look like I've been doing it wrong for too long

Not quite so sure that would be the answer on thin workpieces but for blocks that really looks worth a try.   

Tug


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## pat_pending (Mar 7, 2021)

KenC said:


> Have you seen the video by Joe Pie... on squaring blocks on the mill.
> I found it helpful and I always do it this way.
> Ken



hi Ken. Don't know how i missed your reply. Apologies! Thanks this is really helpful. The 'bad' way using the wire and then an engineers square that he referenced is of course exactly what I was doing LOL. I'll give this a try. I unfortunately converted my mill to CNC a few years ago (which I regret). These sort of 'just skim a bit off here and there' operations now take considerably longer! I'm getting faster at typing raw GCODE but still miss being able to do things by 'feel' as I do on the lathe.

Patrick


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## Ramon (Mar 7, 2021)

Hi Patrick, Ken,

I tried this method on a slab of cast iron about 30 x 25 x 75mm this last week. Sawn on all four sides but gripable in a vise it proved a very viable and quick way of squaring up. Excellent idea and well worth passing on - thanks Ken.

Keep on tapping that G codeout 

Tug


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## pat_pending (Mar 22, 2021)

Hi All,

finally managed to get some quality shed time in over the weekend. Work has been too tiring to get any evening sessions in so slow progress at the moment. I had another crack at those front housings using the advice you all gave me and looks like success  . I used the expanding mandrel with the 60deg cap screw which worked an absolute treat. It did really only take a tiny bit of force on the cap screw to get a tight grip.

I also managed to recover the other two housings using the Tug Insert and Loctite method which seems to have saved em. The bearings are in and they spin great + the housings seem really airtight too. All-around happy, some pics below. Is this two engine build turning into a 3 engine build? 


Thanks again for all the tips. Onto those conrods next so hopefully i can pick up a bit of pace.

Patrick















Here's the mandrel. I finished the final size after slitting + de-burring to make sure everything was as true as possible and compensate for any runout on the 3JSC chuck.






Shim Lockited (is that a word?) in and cured for 24hrs. Ready to machine.






Good as new... and true!






Finishing / profiling operations on front-housing #3.


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## Ramon (Mar 22, 2021)

Well done Patrick - looks like you are back on track. BTW an expanding mandrel _should_ always be trued after slitting. They are certainly useable again but rarely run true so have to be re-trimmed for something smaller.

Regards - Tug

PS there's no k in Loctited


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## pat_pending (Mar 23, 2021)

Ramon said:


> PS there's no k in Loctited



Typo fixed  . Will recommend this verb is added to the dictionary


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## jetstuff (Mar 24, 2021)

Is it possible to make the crankshaft in two pieces? (say....  silver steel shaft and EN24T web)  and also the crankpin from a needle roller? I hate making the interrupted cut on the lathe,  

thanks
john


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## Ramon (Mar 24, 2021)

John,

All the 5cc diesels save one I have made so far have had a composite crank shaft as you describe but with a integral crankpin.  The inner shaft is best made from a caphead screw. I use this as material _not_ for the thread - that is screwcut when the entire shaft is finish turned. The pin area is first milled to a square section to minimise the period of interupted cutting on the lathe

If you check this thread - ST-32- about halfway down the page you'll see how I went about it

Needle rollers make fine pins but it has to be a good interference fit and a decent web thickness to work successfully.

Tug


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## xpylonracer (Mar 24, 2021)

Jetstuff

I don't think silver steel is the best choice for the shaft, EN16T or EN24T throughout or do as Ramon does because he has proven his method beyond doubt.


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## jetstuff (Mar 24, 2021)

Thanks chaps, I have just made a shaft to convert a PAW 15 to a twinshaft, using (what I bought as EN24T) , I get a horrible finish, even using power feed and very light cuts. The first one got the (threaded end)  bent during production between centres, this one is a bit better (in the four jaw chuck) but not great....still got some learning to do!


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## Richard Hed (Mar 24, 2021)

jetstuff said:


> Is it possible to make the crankshaft in two pieces? (say....  silver steel shaft and EN24T web)  and also the crankpin from a needle roller? I hate making the interrupted cut on the lathe,
> 
> thanks
> john


Yes, interrupted cuts can actually damage your lathe if you are not careful.  What size lathe have you got?  I thinmpfk that there isn't a person out there who actually "likes" interrupted cuts.


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## xpylonracer (Mar 24, 2021)

Depending on what tooling you use, HSS or Insert type, you may achieve a better finish with heavier cuts, that applies especially to insert tooling, even the ground type intended for non-ferrous materials, perhaps a cutting fluid will help.


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## Ramon (Mar 24, 2021)

Jetstuff

If you prefer to use it by all means use carbide tooling to rough your shaft to within 10-20 thou on diameter. Then switch to a freshly ground HSS knife tool with a slight radius for the final cuts.

EN24t will cut very nicely with a sharp tool but if the cutting point has even slightly worn it has the propensity to more burnish the material and remove nothing on the last couple of thou or so. The tendency then is to try another thou and still nothing comes off then perhaps another and suddenly the tool digs in and is under that 'skin' and the job is undersize. 
I turn all my shafts to within 20 thou on diameter then regrind the tool for those last cuts to one to two thou up (max) polishing that last amount off with a fine file and or emery/wet and dry paper

Tug


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## pat_pending (Mar 25, 2021)

Per John's original question above, I'm assuming a composite web and pin assembly wouldn't be possible as it would be too difficult fit and mount the pin with precise enough alignment? I used that approach on the Webster (silver soldered in) but the level of accuracy required on that engine is at the 'Garden Engineering' end of the scale vs these 14,000+ RPM aeros.

Patrick


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## Ramon (Mar 25, 2021)

Patrick - Yes it is possible and several builders do use part of a needle roller for the crank pin - it is ideal material infact but it does, as you assume, have to be a very good interference fit and pressed in perfectly in line with the shaft. Not impossible nor exactly difficult but theres only one go at it. It's major limiting factor from my perspective is the limited thickness of the web relative to the diameter of the pin fitted. I've only done it the once and despite taking real care still was not convinced on the outcome.

I long ago was told before finally realising there are no shortcuts in enginering - just roads to further problems if taken.

Removing the waste around the crankpin in tough material and indeed the diameter of the shaft in the initial roughing are ops that just have to be accepted as a tedious part of the build and ones that take time on the basic home kit that most of us have at our disposal.

I much prefer to take small depth of cuts and a higher feed rate but whatever way it's not a job that can be 'pushed' or rushed. To my mind 'accept it as such' and it soon is out of the way ready for those final finishing ops.

Tug


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## jetstuff (Mar 25, 2021)

Thanks again chaps. When turning between centres, what's the best procedure? The first shaft got hot, expanded and bent ! (with a locked live centre). It's a 7 x 65mm shaft with a M6 thread, on a Colchester bantam. 

john


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## Jasonb (Mar 25, 2021)

Sort out why it's getting that hot, your previous poor finishes may well be linked. Bigger jobs I would just unlock the tailstock barrel and take the pressure off and then reapply and lock every so often but something that small with little to come off should not be getting hot enough to cause problems.

On the subject of separate crankpins I have done 3 aero engines all with pressed in Silver steel (drill rod) pins and they ran OK for the odd few bench runs I've ever likely to do with them.


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## jetstuff (Mar 26, 2021)

Jasonb said:


> Sort out why it's getting that hot, your previous poor finishes may well be linked. Bigger jobs I would just unlock the tailstock barrel and take the pressure off and then reapply and lock every so often but something that small with little to come off should not be getting hot enough to cause problems.


It's getting hot because I'm machining a 20mm bar of EN24T down to 7mm without coolant


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## xpylonracer (Mar 26, 2021)

Jetstuff

A way round the problem you found is to rough out oversize the length of shaft + a parting allowance with the EN24T 20mm diam stock mounted in the chuck, centre drill the end before parting off, fit the part to the chuck and face and centre the parted off end. Mount between centres to finish to size.


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## pat_pending (Mar 31, 2021)

Hi, a bit more shed time today. I have finally found the parts I like making the least: Conrods.... or at least this is the first time I've done it and it still honing the technique. They turned out OK (accurate where it counts) but the profiling is still a bit iffy. 

I used the approach detailed on modelenginenews.org linked below:



			Making Conrods for Model Engines
		


Anyway heres the build log.

It all started from a piece of Alumec 89 which Tug kindly let me have. This stuff is hard as nails and v difficult to saw! I shaped a block to +5mm oversize in all dimensions then drilled the big/little end holes ( -0.2mm for reaming later)












Next up I used a slitting saw to cut off slices of the conrod width + 0.5mm.

I then proceeded to surface the width to size and once finished, centre drill at the big end for turning between centres.








Once done i popped the blanks into the 4-jaw and turned with my first ever hand ground HSS tool with 45deg edge. Worked OK for first try but could use some practice. Felt pretty blunt. That Alumec turns great and gets really shiny. The only trouble is it's so hard that the burrs are a bl**dy nightmare to remove!







Next up I made a jig to profile the conrod ends. The brass disks are the desired final diameter of the ends.






Time for hours of hair-rasing machining with fingers just milimeters from the endmill. 






All OK apart from one below that was snatched by the endmill and got destroyed. The Alumec killed the HSS endmill too! That is some strong stuff! Lesson learned: if its trying to snatch the part, tighten up the jig and take lighter cuts.






Anyway, here they are.  They will work and look a lot better after some deburring.






On to some easier bits next. Think cylinder heatsink or prop drivers. 

Bye for now,

Patrick


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## Tim Wescott (Mar 31, 2021)

On your tool: it looks like you're using a fairly coarse grit on your grinder -- you may want to get a finer grit wheel if you want to invest in this (my grinder has a coarse and a fine wheel, all the time).  Even so, the cutting edge should be sharp -- make sure that you've relieved it enough -- if the aluminum is riding on steel right below the cutting edge, it won't cut well.  Finally, I keep an Arkansas stone, which I use to hand-stone the cutting edges of my home-made tools.  This gets rid of the grinding marks, and puts a nice final edge on things.

I usually stop at a medium Arkansas stone -- but I have a super-fine one for if I'm feeling picky.


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## pat_pending (Apr 1, 2021)

Tim Wescott said:


> On your tool: it looks like you're using a fairly coarse grit on your grinder -- you may want to get a finer grit wheel if you want to invest in this (my grinder has a coarse and a fine wheel, all the time).  Even so, the cutting edge should be sharp -- make sure that you've relieved it enough -- if the aluminum is riding on steel right below the cutting edge, it won't cut well.  Finally, I keep an Arkansas stone, which I use to hand-stone the cutting edges of my home-made tools.  This gets rid of the grinding marks, and puts a nice final edge on things.
> 
> I usually stop at a medium Arkansas stone -- but I have a super-fine one for if I'm feeling picky.


Thanks Tim, I'll give that a try. Its high time that I immersed myself into the world of tool grinding as 'real' model engineers do   Looking forward to learning the craft!

Patrick


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## pat_pending (Apr 6, 2021)

Hi all, i managed to get bit of shed time mixed in with the Easter festivities and had a crack at the cylinder heads. They turned out OK although I made a mistake in locating the screw hole on one of them (plus that one has a dodgy fin) so reckon that 3rd engine will be for fitting to a plane or running experiments rather than something for the cabinet. The better heads have 2 variations: 1 with 6 fins per plan and one with 5 as machining those thin fins gave me the fear.

I cut the fins with a parting blade as shown below but wondering if there is a better way. Once the blade gets a bit deeper, the rolls of swarf seem to jam every now and again which, those thin fins, was only a whisker away from disaster. Thinking some sort of chip breaker on the top of the blade might help. Will research for next time. Also i think i would machine the fins while a big lump pf bar stock is in the lathe rather than on the mandrel. Although the mandrel gripped ok, this operation exerts a lot of force on the part and at times there was a bit of slip.

Advice above about the 0.2mm radius inserts and lube worked a treat. I'm really chuffed with the surface finish although may have to 'dull' if I get round to anodising.

Anyway, I think I'll tackle the back parts next including that valve arrangement once I get my head around the plans. The keen observer will note that I'm putting off the cylinder liners which requires making a bespoke slitting saw, angled work-holding in the mill and possibly square hole broaching.... can't avoid for ever 

Anyway, here's the result and the build.

P








I first drilled and bored out the blanks to exact  with generous additional material on the outer faces. I used a plug gauge to get to a close fit and then made a mandrel out of EN1A to the exact same size. Only problem here was that i needed to tighten the mandrel through the compression screw hole which limited me to an M4 cap head. This didn't really provide great holding force on a 17mm mandrel vs say a M6/M8 but i got away with it.





Next up thread the M5 compression screw hole. Figured I'd do this now while the outers weren't finished yet and wouldn't risk scratching anything up/breaking a tap later in the game.





Now mount on the mandrel and machine the outer and the compression screw 'dimple' to +0.5 mm 






Locate on the mill using the lovely smooth surface.






Drill and countersink the mounting holes. Figured the drill would wander less and there would be less cleanup of burrs to do if I drilled the holes first before cutting the fins.I used a 3.3mm drill for M3 holes to give them some breathing space and be a bit forgiving on any slight inaccuracy due to the deep hole drilling.







Back on the mandrel and cut the 2mm radius/chamfer on the outer edge. The lengths I will go to to prevent having to learn HSS tool making  Here I use a chamfer/router bit or the exact radius and used it as a lathe cutting tool. Cheap as chips and seems to work really well.





And finally for what seemed like 10 hours cutting fins. As mentioned above, the parting blade approach wasn't optimal but I just about got away with it. If you look closely at the fins above, there were some that were a bit thinner than others. This wasn't me being a 'numpty' on measurement as I advanced the cross slide precisely using the graduated collars between each fin. I was a bit stumped as to what was going on but I observed the parting blade cutting on the side (rather than just the tip) after I had jammed on the swarf. I think either what happened was that the blade shifted in the holder after this or (more likely) the jammed swarf bent the thin fin and upon release, the blade would cut it straight again. Either way. Hair raising experience and I need a beer now.







The last operation was to put a 4-5degree taper on the head. I did this with the cross-slide once again

More to follow,

Thanks,
Patrick


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## Jasonb (Apr 6, 2021)

The swarf tends to catch less if you do the screw holes after cutting the fins.

Good to hear the inserts worked for you.


----------



## pat_pending (Apr 6, 2021)

Jasonb said:


> The swarf tends to catch less if you do the screw holes after cutting the fins.
> 
> Good to hear the inserts worked for you.



Thanks Jason, the funny part was that while cutting the 'interrupted' part through the holes, everything was great/no jamming as the swarf seemed to come out as chips and fall away nicely. It was at the beginning after about 2mm deep where the swarf was coming out as rolls/curls that would keep getting bigger and bigger and then jam. Not an expert but could it be back rake that I need in order to break the chips and prevent forming the rolls? Apologies if this theory is ridiculous, I'm a tool grinding novice.


----------



## Jasonb (Apr 6, 2021)

I can't quite make out what's going on with the top face of your parting tool, it looks to have two facets but not sure if that is a shallow V or pointing up.

A tool with a concave top surface along it's length will tend to fold the sides of the swarf inwards making them narrower than the slot so less likely to jam, insert tools have this feature.  You could also try some additional top rake on the tool - top surface sloping down from the cutting edge which suits aluminium more.  A faster feed will also produce thicker swarf which tends to break easier than thin which will curl.

Myself I tend to use a couple of insert tools for fins though do have a similar one to yours that is used when the gap is narrow but deep. This is the wider GTN2 insert in action on some 30mm 6082, curls but does not jam in the slot


----------



## pat_pending (Apr 7, 2021)

Thanks Jason. Look at that thing go! 

Yes I have a carbide set too trouble is the thinest i could find is 2mm. The blade i have got me to 1.4mm. On doing some looking about, I think I'll try this sort of shape next with plenty of back rake (picture courtesy of the Arc Eurotrade website


----------



## Ramon (Apr 9, 2021)

It looks to me Pat that your parting blade top face had not been ground eg as per the last image. Possible issue with inserts is that they may not always give you the width required. HSS ground with a top rake and a drop of paraffin makes cutting these a fairly straight forward operation. If the groove is a wide one best to gash it first with a narrower tool.

I prefer to cut fins after drilling the holes - two reasons - main one is that it is much easier to deburr the holes with burrs inside the holes than to try to deburr the burrs inside the fins if drilling is done after.
Second one is that the holes are less likely to wander when drilling from solid than constantly having to re centre on each fin. Taller the head the more likely this occurs

If you are restricted on caphead size on a mandrel relieve the diameter considerably behind the gripping area. The gripping area does not have to be particularly wide relative to diameter.

Good to see some more progress - Tug


----------



## Tim Wescott (Apr 9, 2021)

Ditto on making the parting tool face concave on top.  You can do this with a Dremel Dangerous Disk if you have steady hands.  The resulting tool isn't pretty, but it does keep the chips from sticking -- and you have to be a good friend before I'm going to let you into my shop to inspect my tools.


----------



## Ramon (Apr 9, 2021)

I would certainly agree that a concave top surface will help the 'chip' (coil?) to release more easily but I have never bothered to do so on any of the parting tools I use as it is not the easiest of operations to do with a degree of certainty. All things are worth trying though but as long as the sides are backed off slightly so no rubbing occurs and the tool has a decent top rake and sharp cutting edge on or very slightly below centre height a normal parting tool will work fine on this particular operation. The biggest issue to prevent is rubbing, the ali building up quickly and jamming. Paraffin dripped on from a squeezy bottle or applied by brush helps prevent that situation happening considerably. 
Some advocate WD 40 - only caveat on that (for me) is that the fumes created by heat can cause respiratory problems - that's based on personal experience using it on lathe work at work. Readily available and used in liquid form and a spray bottle at my last place of work it did not take long to manifest itself in my lungs to a severe degree in quite a short space of time. 

Regards - Tug


----------



## pat_pending (Apr 10, 2021)

Hi All,

a bit more progress over the last couple of days. I tackled the backplates which at first seemed simple but posed me all sorts of work-holding issues and a few bloopers along the way. I got there in the end and am really chuffed how they came out. The fit in the the 2 made crank cases is just perfect. I still need to make the 3rd crank case so can fit to the backplate when I do,

I was thinking of making the rotor and pins next but have got myself tied in knots trying to find 'Tufnol or similar' as is called for in the plans. On ebay a rod of 40mm x 300mm is 70 quid!! If you go to a specialist plastic supplier there are a load of options regarding the fiber coarseness etc. What do people out there use? I have Nylon rod to hand would that do?  Delrin (POM-H (Polyacetal - Homopolymer) seems to be another option and more easily available at a reasonable price with a service temperature of 120-150C and a melting point of 180. No idea what this is like to machine tho...












One slight issue is that i rounded up the countersink hole on the rear Venturi hole and it ended up jut puncturing the edge of the register on one of the backplates by a **tiny** bit. Im pretty sure with a tight-fitting Venturi Loctited in as the plans call for there wont be any crank-case pressure loss but time will tell.

Here's how they were made (my workshop instruction sheet):


Square 3 blocks of stock 30X30X13.
Centre drill
Drill the venturi hole 6mm at x-8.46 y1.295 (left up)
Drill the 4 mounting screw holes at 3.3mm. 10.775mm from the centre
Mount in 4-jaw and centre on the register mark
Face to make sure everything is square
Drill the pin hole at 3.3mm
Countersink the pin hole 3.18 depth 5mm diameter
Tap the pin hole M4
Turn the register 4.5mm deep making sure to creep up on the crank cases to make an airtight fit.
Use hight gauge to mark 11.4 mm
Mount in mandrel and face to correct total length 11.4 mm
Turn down the pin retaining nut dimple 4.22mm
Mount in mill and centre on the venturi hole.
Countersink venturi hole 7mm to 5mm depth (I did 8 but this turned-out to be just too big)
Chamfer edges and final size to match crank case.







The pieces drilled. Oh look another mandrel!






I have started using a centre between centres to locate on the 4-jaw now rather than using my 'wiggler'. I find the centre sits in the hole a lot better and doesn't move about.







Turn down the register and countersink the pin hole.






The parts ready to mount on the mandrel and turn the back side.






Mount on the mandrel and turn the other side. I trued the mandrel but then realised i needed to remove it from the chuck again to bolt the part on from the back! . Rather than disturbing the mandrel in the 3JSC, i removed the chuck to mount the part instead. This seemed to work OK. I wouldn't do this on a part that has to be absolutely true but this was just for turning the 'dimple' for the rotor pin retaining nut to sit on so all good.






Next I counterbored the venturi hole. Warning, 8MM is too big! I would have waited and bought a 7mm endmill. :-(






Lastly I mounted the plates up and scribed out the outlines of the crank cases. This allowed me to get a good mating with the crank-vase shape. Still not perfect but satisfactory.


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## jetstuff (Apr 11, 2021)

Not sure why you would need a 300x 40mm piece of Tufnol/Paxolin for an engine, is it for a disc valve? available in sheet form easily for a few pounds.


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## pat_pending (Apr 11, 2021)

jetstuff said:


> Not sure why you would need a 300x 40mm piece of Tufnol/Paxolin for an engine, is it for a disc valve? available in sheet form easily for a few pounds.


Hi, yeah it’s for a disc valve. I was thinking of getting it in rod form to avoid trapanning a sheet of mucking about with a hole saw but I’ll take a look. Any tips on the grade to go for/where to find it? Thanks, P


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## Ramon (Apr 11, 2021)

Hi Pat

If you noted in any of the builds I have done all rotors made from tufnol are turned from small blocks cut from thickish sheet and then the cut out and relief milled. The first RV engine I made I heard about oil filled nylon so made a disc from it. I later found that this can distort with the rotational forces so have made them from scraps of Tufnol ever since. Though I have not used it for this specific purpose I'm not sure Paxolin would be a good material as it can chip and crack.

If you can find some 1/4 thick sheet, mark out and drill the central hole then rough bandsaw it out. Put it on a mandrel to turn the od then make an ally clamp plate to hold the OD whilst milling - you will need a rotary table for that for the best approach.

Tug


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## xpylonracer (Apr 11, 2021)

Sheet form will suit the application as the cloth will be laminated in the thickness plane.


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## Jasonb (Apr 11, 2021)

And if you don't have a bandsaw it cuts easy enough with a hacksaw, cut a square then cut the corners off then onto the lathe


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## Ramon (Apr 11, 2021)

Hi Pat just found these pics for you which may help





















That should be self explanatory but if not just say. The green one is the oil filled nylon - though it worked I wouldn't recommend it 

Tug


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## pat_pending (Apr 11, 2021)

Great. Thanks for all the replies. V Helpful.  Last question I have is whether Tufnol is Tufnol if that makes sense? If I buy a sheet off eBay are there different grades that may suit better than others or am I overthinking this one? (Likely!). P


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## pat_pending (Apr 11, 2021)

Ramon said:


> Hi Pat just found these pics for you which may help
> 
> 
> 
> ...


Oh perfect thanks. I love that holding approach. I have the rotary table ready for action! P


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## Ramon (Apr 11, 2021)

Hi Pat - like many materials Tufnol comes in different grades all named after fish I believe. Most if not all will be suitable for what you are doing. As said beware of 'Paxolin' as this is paper based not cloth as Tufnol is. Thin sections are very prone to splintering/chipping. Personally though I have paxolin I would not use it for this specific use.

Some recommend the 'as produced' finished face as the running surface - I've not seen any advantage of that but what is important is that the running face is truly square to the bore so best to machine this face and take a very fine finishing cut through the bore to ensure this. Make the pin diameter to fit.

Tug


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## pat_pending (Apr 11, 2021)

Ok. I got some of this. 









						SRBF fine weave  Sheet  in 8, 10 or 12 mm thickness Tufnol CARP or equivalent  | eBay
					

SRBF Sheet F1 (Fine weave Grade).



					www.ebay.co.uk
				




Thanks for the advice. Will report how I get on. P


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## Mechanicboy (Apr 11, 2021)

In my ED Seaotter has disc made of black plastic instead Tufnol. Maybe made of nylon or heat and wear resistant plastic material.


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## Billitmotors (Apr 12, 2021)

G’day Pat when I made my pair of Naylon Vipers I used Delrin for the discs. They worked brilliantly. I have used delrin on at least 6 other engines without any problems.


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## Billitmotors (Apr 12, 2021)

I forgot to mention you can buy delrin in rod or sheet form as well. Also you don’t get the furry fibre on the cut edges.


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## pat_pending (Apr 12, 2021)

Billitmotors said:


> I forgot to mention you can buy delrin in rod or sheet form as well. Also you don’t get the furry fibre on the cut edges.


G-day mate. Thanks for the tip. I had heard of people making gudgeon pin end caps out of it without issue so I assumed it must be OK as that is a MUCH hotter part of the engine. P


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## Billitmotors (Apr 13, 2021)

Gday Pat
I usually use teflon for my gudgeon pin end caps.


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## pat_pending (Apr 15, 2021)

Ramon said:


> Hi Pat just found these pics for you which may help
> 
> 
> 
> ...


Hi Tug, 

Just to be sure i understand (being a beginner muppet/novice) the sequence you are describing is as follows.

1) Rough out a piece of the Tufnol on a band saw. 
2) Drill through
3) Mount on a mandrel in the lathe using that centre hole and make a generously oversized round.
4) Mount on rotary table locating on the outside of the round.
5) Mill the outer shape and holes to finished dimensions
6) Pop the round back in lathe and part off the disk valve (oversized e.g +1mm)
7) Mount the disk in the lathe in a pot chuck and face the back.

My worry is that the centre drilling and other operations are in different setups and some error might creep in to how perpendicular all the surfaces holes remain to that first hole where the pin goes. If i drilled that first hole undersize for the mandrel mounting then opened it up when the part is on the rotary table would that solve the problem? 

Am I over thinking this?

Thanks and apologies for the noob questions.

Patrick


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## Ramon (Apr 15, 2021)

"Am I over thinking this"

Hi Pat, No, not at all, you're well on track with that procedure.

However as said before the most import thing is to get the running face (next to the backplate) as square to the bore as possible. The best way to ensure this is to take a very fine skim out of the bore when you skim the rear face in the pot chuck. 

You can either make the central hole for the initial turning slightly smaller than finally required and bore the hole to suit the pin or,  skim the bore slightly larger and make the pin diameter to suit the enlarged hole.

No apologies needed - for a self confessed 'muppet' you are doing remarkably well   

As Billit said you do get a 'furry' edge when machined but that's easily dealt with with a swipe of wet and dry paper.

Regards - Tug


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## pat_pending (Apr 18, 2021)

Hi, limited shed time as the garden has sprung into life and required attention / attacking with motorised implements. I did however get those valves done which turned out to be quite straightforward using the tips received in this thread so thanks again.

In the end I used Delrin just because it arrived first from eBay and turned out to be really easy to machine to a nice finish. Im happy with the result. Im assuming as everything (outer, face, holes, counterbores) were done in a single setup, everything should be nice and square. The facing of the rear side of the valve was done with the front side pressing against the back of the pot chuck so i'm thinking this will be parallel enough. I took measurements at the edges and they came out spot-on so I think I'm OK).

On to making some venturis spray bars and prop drivers next as gardening allows.

-P







Build was as follows.

Mount stock in the rotary table, face and turn the final OD with a 8mm 2-flute HSS mill.






Cut the profile, drill the pin hole, crankpin hole and countersink etc.






Part off the valve in the lathe with a decent bit of extra material for facing to size later.





now mount in an aluminium pot chuck and skim to final with. With the first part i needed to remove, measure and re-mount a couple of times to get the with spot-on. Nice thing with this fixture is that since the flange on the pot chuck sits against the lathe chuck jaws, subsequent valves could just be mounted and faced at the cross-slide position left for the previous part.


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## pat_pending (Apr 19, 2021)

I managed to burgle a few hours today and had a go at those prop drivers. Loads of great advice out there but in the end I went for the modelenginenews.org approach which seemed to match my skill level/experience well. This is exactly how I made them for the BollAero although somehow, the previous set caused lass drama + less scrap in the bucket. Maybe last time was beginners luck? Im happy with the result but I think the final fit needs to be made with a prop tightened-up. At the moment I have left about 1mm space between the driver and the bearing but the brass collar isn't really gripping the shaft yet. Hoping to get lucky and this gap will close up perfectly. Else I'll just skim a bit more off the back of the driver so no issues there.

On reflection, I think the BollAero collars were easier to trial fit as they were really, really thin perhaps 0.1mm at the thin end of the taper. this meant that on a test fit you could push down and the assembly would grip immediately. Here, these things as specified are big old 'wedges' so this requires more force to contract around the shaft. Perhaps this will make subsequent removal easier?..

Anyway, heres how I made em

Turn and knurl the prop driver blanks including the prop nut recess. I took the decision to relieve the edge a bit so any burrs created by plunge knurling wouldn't spread past the edge both inner/outer. I needed a snug fit into the pot chuck later so wanted to avoid lots of deburr/emery papering.












I realised i didn't actually bother taking a picture of the plunge knurling but standard stuff. Lots of WD40 and a brush to wipe the chips away as soon as they start clogging the wheel.







Next up the cross-slide was turned to 10 degrees and a taper was cut in some tool steel.






Next the brass collars were cut at the exact same cross-slide setting.







The tool steel was cut away for a 'smidge' under the centre line, hardened and tempered.









The bits now ready for final seating.





Drivers now reversed and mounted in a pot chuck . The taper was expanded out with the 'D' bit reamer and lots of test fitting,






Fit too loose for the finished article but will fine tune when I've been able to tighten everything up properly. Also the bearing sits a tiny bit proud to the crank case. Once the prop is tightened up and everything is sitting properly I'll take a call on whether to stick the crankshaft back between centres snd skim the bit that the bearing sits on. Easy operation but would be a pain in the a*** to break something that late in the game.


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## Tim Wescott (Apr 19, 2021)

How did you do the actual knurling?


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## pat_pending (Apr 19, 2021)

Hi Tim, that was the one photo i forgot to take as I was too in the 'zone' dusting away swarf etc. It was a straight knurling wheel (eBay Chinese variety) plunged directly into the face of the driver. I counted micrometer marks and pushed the wheel in 0.8mm with lashings of WD40 which seemed plenty for a deep knurl.

-P


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## Ramon (Apr 19, 2021)

Hi Pat - further to your PM.

I make the tooling to cut the exhaust slots from either guage plate or silver steel.
I make this as a small cutter which attaches to a separate shank with a cap screw






The blank is turned first then the teeth cut in on the mill. The leading edge of the tooth is behind the centre line of the cutter to give positive rake to the tooth.

Each tooth is backed off by hand filing then the cutter is heat treated and quenched in oil. It is not tempered. This gives maximum hardness for the small use this will have. The teeth are finally finished by diamond file.





This is the one I made for the Eta engines - it did six liners without a hitch in EN1a free cutting steel. I prefer to do this dry as without flood coolant to get the swarf away any coolant applied by brush tends to make the swarf stick and crowd the cutter. Speed well down and feed to suit.






The three liners from the second batch. The transfer passages were not broached but drilled first then the passages milled and finally filed by hand to rectangular section. I made a very thin walled sleeve that registered on the top of the liner to reference the position of the top of the transfer 'cut off' inside the liner






Rather than answer by PM I though that may have interest for others.

Hope that helps you though 

Regards - Tug


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## pat_pending (Apr 19, 2021)

Ramon said:


> Hi Pat - further to your PM.
> 
> I make the tooling to cut the exhaust slots from either guage plate or silver steel.
> I make this as a small cutter which attaches to a separate shank with a cap screw
> ...


Thanks Tug, that’s really helpful
.
I assume you made the cutters on the rotary table? I can picture making the leading edge of the tooth (noted what you said about positive rake above) I’m just not sure about cutting the back of the tooth. Possibly this is one of these operations that will be obvious once I get started. Looking closely at the profiles above it looks like each tooth has 3 cuts to it ( same endmill, rotary table advanced, different depth of cut). Is this how it was done?

thanks, P


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## Ramon (Apr 19, 2021)

Hi Pat - 

I cut my teeth on the cutter shown using a dividing head with the embryo cutter shank horizontal but a rotary table will do the same if set up horizontaly. It can also be done vertically of course. Unfortunately I don't have any images of actually cutting the teeth but the depth of cut will set the rear face of the next tooth. Unless you draw it out first it's a matter of going round a few times increasing the depth until the proportions look right. Backing the teeth off so they dont rub is where the main attention needs to be. Bear in mind it's only the very outer edge that does the cutting but you don't want the cutter to rub. It's a good idea to radius the corners of the milling cutter used to cut the teeth so no stress point is created at the gullet 

Tug


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## pat_pending (Apr 20, 2021)

OK great i think I'll draw it and maybe have a go on some wood/acrylic first to get my 'eye in'.

By 'backing off' I assume you are referring to the shape i've highlighted red below? 



-P


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## Ramon (Apr 20, 2021)

Hi Pat, 

No,  backing off is the reduction in thickness behind the edge you have in red (the silver areas). That red line is your cutting edge and that should be as close to as machined as possible. I think you are showing an early cutter made. This had each side tapered inwards on the lathe to give some clearance then the relief angles were filed. This worked but it meant that only the very tip of the teeth were controlling the finished dimension of the slot. These cutters need to do the slot to finished size in one go for best result.

The type shown before held horizontally and milled with the end of the cutter and not the side perform much better.

Heres a slightly better picture of doing an Oliver liner which may help





Regards - Tug


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## pat_pending (Apr 22, 2021)

Ramon said:


> Hi Pat,
> 
> No,  backing off is the reduction in thickness behind the edge you have in red (the silver areas). That red line is your cutting edge and that should be as close to as machined as possible. I think you are showing an early cutter made. This had each side tapered inwards on the lathe to give some clearance then the relief angles were filed. This worked but it meant that only the very tip of the teeth were controlling the finished dimension of the slot. These cutters need to do the slot to finished size in one go for best result.
> 
> ...


Thanks Tug, that's really helpful. Will make a few experiments tomorrow to see how I get on. I happened to find a cutter of the exact dimensions in the US (50$ +26$ postage!) or made to order in the UK for £120. I think this really is one of those cases where there is no alternative 

P


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## pat_pending (Apr 22, 2021)

Hi, I got a bit of time in the shed today and got started on the carburettor parts and the rotor pins. Will post pics of the carbs when all finished. I really am running out of bits to make before tackling those dreaded cylinder liners!






I tried the tempering using the hot sand method following Tug's ETA build thread. Mine went straw rather than black but perhaps thats because I was using D2 tool steel not silver steel?  Anyway, they worked out OK.

I used a bit of copper tube squashed down and tapped to hold the pins. This seemed to work a treat. Beware, the copper conducts the heat a LONG way up the tube and doesn't get cooled down through the quenching... Don't ask how I know. After the heating to what, in my opinion,  looks like a cherry colour, I kept it there for about a minute then quenched in oil. I was carful to have the pin square to the oil to minimise distortion. 






I then sieved some sand and heated it for a long time while stirring to get out any moisture (I'm sure the dog wont miss her food bowl  ). The bowl was glowing red at the bottom and I must have heated for a goof 20 mins. Checking with the Maplin cheepo IR Thermometer, the sand was showing 320C and I couldn't get it any hotter.

At this point I stuck in the pins that had been cleaned and made shiny again on the top surface. I watched closely until the 'straw' colour came and went. i was hoping for that nice black Tug got on the ETAs but I think this was all i was going to get with the D2.


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## 777engman (Apr 23, 2021)

pat_pending said:


> Hi, a bit more shed time today. I have finally found the parts I like making the least: Conrods.... or at least this is the first time I've done it and it still honing the technique. They turned out OK (accurate where it counts) but the profiling is still a bit iffy.
> 
> I used the approach detailed on modelenginenews.org linked below:
> 
> ...


best to do this op with a rotary table, that never happens then, I've made several hundred con-rods and not had any of them do that. discovered the rotary table option after your experience happened to me once, nearly lost a thumb.
Regards
Dean


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## pat_pending (Apr 23, 2021)

Thanks Dean. Ideally I’d like to be a bit further away from the cutter for sure. I’m sure it’s obvious but you don’t happen to have a pic/description of your process/fixtures ? That would really help.
Patrick


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## pat_pending (Apr 24, 2021)

Hi All, 

i had a go at the cutter this morning. Bit rough n' ready but seems to work! When cutting it feels like one tooth seems to be 'banging' the workpiece every revolution. I'm not sure if this is runout on the arbor or one tooth is a tiny bit longer than the others. I'll inspect before cutting the final liners. I tried out in some EN1A i had lying in the scrap bin and it seemed to so do a really clean cut without any burrs. 

In the end I cheated and CNCd the profile of the cutter then deburred + backed off the teeth with a file (you can just about see in the pic) then hardened and touched up with the diamond file.

Reckon this will do the trick although the cutting experience seems a bit 'violent' rather than beautiful curls of swarf coming off and being carried away by fairies. 

Just getting my head around making those liners now. Recon I'll make a start tomorrow.

-P


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## Ramon (Apr 24, 2021)

For a first go that's pretty good Pat. However looking at the third image it appears you have a slight negative angle to the teeth at the tips. Try gently improving that to positive on the corner of a grinding wheel (bench grinder that is) - don't let it get hot as it will temper beyond use and try not to remove the very outer cutting 'edge' when doing so. It's not important that all teeth are symetricall but getting it to cut efficiently is. Any rubbing or forcing will create heat which will quickly dull the cutter.

Use a diamond file to actually 'file' to improve the cutting tips - you should have a bright shiny area behind the cutting edge about 1.5 mm wide across the width of the cutter but bear in mind this is backed off from the very tip. Check the cutting edge with an eyeglass to be sure your cutting edges are sharp and that you haven't created a 'land'.

Your test cut does have an appearance of the cutter having rubbed to a degree or blunted slightly. If it's right it should sail through En1a with ease - but you do need to keep the speed and feed well down compared with HSS. Remember - any heat build up and the work is down the tube

I take it you are cutting the ports into a premachined liner after boring and not before?

Regards - Tug


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## pat_pending (Apr 24, 2021)

Ramon said:


> For a first go that's pretty good Pat. However looking at the third image it appears you have a slight negative angle to the teeth at the tips. Try gently improving that to positive on the corner of a grinding wheel (bench grinder that is) - don't let it get hot as it will temper beyond use and try not to remove the very outer cutting 'edge' when doing so. It's not important that all teeth are symetricall but getting it to cut efficiently is. Any rubbing or forcing will create heat which will quickly dull the cutter.
> 
> Use a diamond file to actually 'file' to improve the cutting tips - you should have a bright shiny area behind the cutting edge about 1.5 mm wide across the width of the cutter but bear in mind this is backed off from the very tip. Check the cutting edge with an eyeglass to be sure your cutting edges are sharp and that you haven't created a 'land'.
> 
> ...


Thanks Tug, i see what you mean. I'll have a go at changing the rake on the teeth and see how that works. I was planning on cutting the ports as one of the last operations on machined liners. 

-P


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## xpylonracer (Apr 25, 2021)

Pat, did you do the test cut with the machine in reverse, I ask because the cutter seems to be on the mandrel to suit reverse rotation. ?


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## pat_pending (Apr 25, 2021)

xpylonracer said:


> Pat, did you do the test cut with the machine in reverse, I ask because the cutter seems to be on the mandrel to suit reverse rotation. ?


Hi, excellent observation! Yes I mounted the cutter the wrong way on the arbor but rather than flip it over i just ran in reverse. Running the wrong way would definitely have explained the rubbish cut.

I destroyed the cutter with cavalier filing yesterday so need to rough out a new blank. Rather than a flat cutting face I've added 8 degrees of rake as below. Hope that does the trick.

Thanks,
P


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## pat_pending (Apr 25, 2021)

pat_pending said:


> Thanks Tug, i see what you mean. I'll have a go at changing the rake on the teeth and see how that works. I was planning on cutting the ports as one of the last operations on machined liners.
> 
> -P


Hi Tug, 

i warned you about the beginner questions here  . Is the below (top view of a tooth) what is referred to as 'backing off' ?

Thanks,
P


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## Ramon (Apr 26, 2021)

Hi Pat,

Just keep asking about what you want to know Pat - nothings out of sorts if you don't know the answer.

Yes that is backing off - done so the only part 'touching' is the cutting edge itself. It can be quite crude the only important bit not to spoil is that cutting edge/tip. As drawn in your previous post put a small primary angle on with a diamond file after hardening - losing a little on diameter wont have any real affect but the sharper it is the better. 

Best of luck for the seond attempt  

Tug


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## pat_pending (Apr 26, 2021)

OK, second attempt getting slightly better! I fiddled around with the diamond file a bit and managed to get it to cut almost properly. There are nice curly chips and the finish of the hole is getting better,

I think I will still have a go at the backing off' the teeth tomorrow but this seems to work(ish). I think compounding the problem here is that I really have no experience sharpening anything at all since all my tooling is carbide and lawn tractor blades don't count as i just do those on the angle grinder . I need to take the time to learn and also get myself some stones etc. I have the workshop practice series book on the way.

-P


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## Ramon (Apr 26, 2021)

Pat - looking better but one thing - (I guess I didn't make myself clear) - the backing off behind the teeth should be done using a file _before_ heat treatment. Diamond filing it _after_ is to 'fine tune' the cutting edges. In other words attain the final shaping of the cutter before heat treating and just finish the cutting edges with the diamond once hardened.

I find the easiest way is to mount the profiled blank on a simple mandrel and hold the mandrel in a bench vise so the cutter is in the horizontal plane. File each tooth in turn away from you with the cutting face facing you. Once done turn over and repeat on the other side. If you don't fancy doing another cutter anneal this one - do as above then reheat treat.


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## Billitmotors (Apr 27, 2021)

xpylonracer said:


> Pat, did you do the test cut with the machine in reverse, I ask because the cutter seems to be on the mandrel to suit reverse rotation. ?


G’day Pat
I’ve found that the simplest and most accurate way to cut this style of exhaust Port is to use one of the boring tools that accepts1/8” high speed steel. Use the end that holds the tool bit at right angles to the axis of the tool holder. Sharpen the tool so it resembles a miniature parting tool with extra front clearance and the and the width the same as the port width.  Mount the tool after cutting it to length. Set the tool to give the correct radius. Start cutting it worked well for me.


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## Ramon (Apr 27, 2021)

Hi 'Billitt', nIce one 

I'm a firm believer in many ways to skin a cat and your suggestion is certainly one of them. Flycutting on the side you could say    Feed rate though, I imagine would have to be very fine

Whilst it would undoubtably work however, I can't agree that it would be the 'most accurate' compared to a cutter made for the purpose - equal perhaps but not better. Besides, making a cutter  is a 'skill' part of the process that needs to be acquired as other cutters will at some time be required where such a method isn't suitable.

I like the idea though 

Tug


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## pat_pending (Apr 27, 2021)

Hi All,

I will continue playing with the cutters tomorrow. I decided to keep that one because it works, and make another one to see if I can improve on it. I have a set of oil stones coming off Amazon which I'm looking forward to seeing if I can get a sharper/smoother edge than with the diamond file. I'll of course try the 'backing off' too before the cutter is hardened. 

In the mean time I had a play with the cylinder liner in CAD to get my head around the process of making it. The plans call for a #33 drill hole to made at a 25 degree angle to form the transfer ports. This in it's self doesn't sound that tricky (I might shift the head of my mill. something i rarely do) except for actually starting a hole at that angle. I would imagine chances of success are greatly improved using a centre drill and opening up a decent 'seat' for the drill to start but Im worried about this thing wandering all over the place and killing the accuracy of the whole thing. I'm using EN1A for the liners so at least its quite soft to machine. 

I was wondering if anyone had any advice for me in that regard. CAD Pics below to show what I'm on about .

Thanks,
Patrick


----------



## pat_pending (Apr 27, 2021)

Billitmotors said:


> G’day Pat
> I’ve found that the simplest and most accurate way to cut this style of exhaust Port is to use one of the boring tools that accepts1/8” high speed steel. Use the end that holds the tool bit at right angles to the axis of the tool holder. Sharpen the tool so it resembles a miniature parting tool with extra front clearance and the and the width the same as the port width.  Mount the tool after cutting it to length. Set the tool to give the correct radius. Start cutting it worked well for me.


Hi Billit, that also sounds like a neat option. What sort of edge did you put on the HSS Bit for this to cut nicely? I might also give this a try.

Thanks for the tip.

P


----------



## pat_pending (Apr 27, 2021)

Billitmotors said:


> G’day Pat
> I’ve found that the simplest and most accurate way to cut this style of exhaust Port is to use one of the boring tools that accepts1/8” high speed steel. Use the end that holds the tool bit at right angles to the axis of the tool holder. Sharpen the tool so it resembles a miniature parting tool with extra front clearance and the and the width the same as the port width.  Mount the tool after cutting it to length. Set the tool to give the correct radius. Start cutting it worked well for me.


 Also, just looking at a few of these on Fleabay, I imagine this would have to be a tiny boring head if the radius of the cutout is 0.5". These boring heads in an MT3 all seem to be a lot bigger (or am I thinking about the wrong tool here?).

Thanks, 
P


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## Ramon (Apr 27, 2021)

Pat - last question first. Think of the boring bar as the diameter of the shank of your cutter and the protrusion of the tool bit as the radius of it. You have to have enough depth to give the depth of cut required without the shank (or boring bar) hitting or just touching the liner .

Drilling the holes at an angle requires a flat on which to drill with your centre drill. Once you have established the exact position start off with a small FC3 cutter to give you that flat, perpendicular to the hole. Spot then drill through - be carefull with feed - as you break through the drill can snatch, even break. A tightish aluminiium plug inside the bore will help alleviate this and being ali will not damage the bore if has to be tapped out.

You can use an FC3 cutter to do it in one but the shank has to be ground back to get the depth required (maybe not in a 2.5cc?)





This is being done on the  lathe but set up no different to the mill - the cutter here is quil fed

Regards - Tug


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## pat_pending (Apr 30, 2021)

Hi all. I think I've just about got my head around making these liners. One question remains which I hope someone here might be able to shed some light on.

In terms of the positioning of the transfer port hole, the plans give 2 clues (1) that the hole I'm supposed to drill at a 45deg angle is 0.164" from the liner flange and (2) that once drilling at 45degrees, the upper edge of the whole as viewed from the inside of the cylinder is 0.024" lower than the top of the exhaust post. I imagine this second dimension is the critical one as it sets the timing (also broaching those corners might increase the power quite a bit if memory of  tinkering with 50cc mopeds as a kid serve me well).

So far so good however, if I'm starting a drill at an angle and need to make a flat first with an endmill for the drill to seat as suggested, where would the start point be?

My idea would to line up on the edge of a tooth of the milling cutter by eye on a small centre-drill mark measured on the DRO and then move the axis half the cutter width before starting cutting the flat? I suppose after the flat is made I could mark out the spot again before centre drilling and using the correct sized jobber drill to make the hole?

Im sure there's something obvious I'm missing here or some quick maths I have to do to compensate for the angle. Just feels like this is too critical to get wrong.

Any suggestions greatly appreciated as always.

Thanks,
Patrick


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## Ramon (Apr 30, 2021)

Pat - I assume the '45 degree' is a typo on your part 

You need to establish by maths (CAD) the exact position of entry on the liner of the centreline of the cutter to give the cut off point at .024 below the exhaust as the cutter breaks through. I normally do this from a known edge - eg the lower exhaust flange face or the lower corner after establishing the exact distance from the lower face to the exhaust flange lower face. _ Make sure you are absolutely certain of the right place_ - too low and you can possibly save it but too high and it's a scrapper as far as timing is concerned. Internally it's virtually impossible to measure acurately but you can make simple depth comparisons using a pre set depth guage.

Someone else may have other means to add to this awkward to set up but not too difficult op but that's the way I have gone about it so far

Tug

PS. I have never attempted to broach these holes - a special cutter would certainly need making.

I have Barrete section needle files that I have ground the sides away to fit the hole diameters and file the edges of the transfer ports square but then mine are much larger at 5cc so probably a lot easier to do.

Personally, I would keep as drilled in the first instance and see how the engine runs - the ports can always be tweaked later though you may have to relap the bore and possibly make a new piston after.

another PS.

Regarding positioning, though I have never done it you could scribe a line around the liner at the point of entry and pick that line up with a needle point in the drill chuck to begin with. As said air on the side of caution and be on the lower side of the line rather than above!


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## pat_pending (Apr 30, 2021)

Thanks for the


Ramon said:


> Pat - I assume the '45 degree' is a typo on your part
> 
> You need to establish by maths (CAD) the exact position of entry on the liner of the centreline of the cutter to give the cut off point at .024 below the exhaust as the cutter breaks through. I normally do this from a known edge - eg the lower exhaust flange face or the lower corner after establishing the exact distance from the lower face to the exhaust flange lower face. _ Make sure you are absolutely certain of the right place_ - too low and you can possibly save it but too high and it's a scrapper as far as timing is concerned. Internally it's virtually impossible to measure acurately but you can make simple depth comparisons using a pre set depth guage.
> 
> ...


Hi Tug, thanks for the tips! RE the CAD/Maths bit, is the 0.164" dimension given on the plans not the starting point for the hole? if I scribe a line at this and pick it up with a needle point in the mill (head already at 25deg) would that do it?

I am certain 'all bets are off' in terms of edge-finding etc once the head is at the angle so the scribing/marking-out with reference to the flange has to be done beforehand. Needle and magnifying glass should be good for at best 0.04mm accuracy I would think. Wondering if this is enough.

Good tip on airing on the 'low side' on this. Ill photograph the scrap bucket from this project at some point. It ain't pretty 

Thanks,
P


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## Ramon (Apr 30, 2021)

Hi Pat

True old saying you can learn something every day 

The maths I was referring to was using the cutter to touch on and move to the correct position but....

Until my last post I'd never considered doing as suggested but given an accutrately scribed line relative to the exhaust port height and a true running needle point in the drill chuck the positioning would certainly be accurate enough to put you in the ball park. Even the best of engines of this kind of porting will have slight variations in port timing so this should be more than accurate enough at this stage.

Some times one simply can't see the wood for the trees - if ( and it's a big if) I do make another engine I will certainly try this method of setting up for this op.

_Ill photograph the scrap bucket from this project at some point. It ain't pretty _

We've all got one Pat - man who ain't made a mistake ain't made anything


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## f2cf1g (Apr 30, 2021)

Hi Pat.  I'm following your thread with interest because I'm also building one.  My scrap bin is far from empty!  The drawings show two methods for cutting the transfer ports, the one you are contemplating and another with the flute extending from a hole drilled at rightangles into the bore.  I can't think it helps gas flow so maybe it was simply a way to mount a guide for a broach.  Any views?
Roy


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## pat_pending (Apr 30, 2021)

Playing with cutters some more today but in between I thought I'd have a go at making the needles for the NVAs. I used the procedure outlined on ModelEngineNews How To Grind Needles for NVAs and I'm really chuffed with the result.

I started out with some 1/16" Piano wire. I looked for stuff advertised us 'unrolled' or 'straight' assuming this would be best although I suspect at some point this stuff 'must' have been on a roll (?) keen to hear where people get theirs from and if piano wire is piano wire if that makes sense (in terms of quality/ straitness etc for the job at hand).

I then mounted a rotary tool in the tool post and set the cross slide over to 10degrees. I mounted the wire in an ER14 MT3 collet. Then using a Dremel #85422 Silicon Carbide disk 25/32", i proceeded to gently rough out the taper using the cross slide edging in 0.01mm at a time. The last pass I covered a few times to take the 'flex' out of the wire which had to stick out a bit for clearance.

For all the milling I ran the lathe in reverse at something ridiculous like 2000RPM and the grinding wheel at 20,000. Both got pretty warm after I was done . I also covered the lathe bed for this one to keep all the abrasive dust of my precious cast iron.

After roughing the needles I switched the wheel over to a #425 7/8" Emery Impregnated disk and did some really light finishing passes. After this was done I finished the needles off with WD40d carbide paper going down from 800, 1000, 2000 grades.


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## pat_pending (Apr 30, 2021)

f2cf1g said:


> Hi Pat.  I'm following your thread with interest because I'm also building one.  My scrap bin is far from empty!  The drawings show two methods for cutting the transfer ports, the one you are contemplating and another with the flute extending from a hole drilled at rightangles into the bore.  I can't think it helps gas flow so maybe it was simply a way to mount a guide for a broach.  Any views?
> Roy


 Hi Roy, hope your build is going well. In terms of the two sets of plans, I went for the Viper first prototype one since the idea of messing up the whole cast iron head vs just the liner just seemed too risky given my current skill level. I may still have a go at some point to have both versions in the cabinet.

-Patrick


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## Ramon (Apr 30, 2021)

Pat, Though either will do there is a distinct difference between 'Music wire' and 'Piano' wire not least that the music comes in imperial sizes and piano in SWG.  Piano wire is much harder and springier than music. Most wire sold in model shops from the KS range is music wire and usually has a small label attached to each piece saying so

16 SWG piano wire is just over a 1/16 so won't go into a 1/16 hole unless it drills oversize. A piece of it however can be turned into a reamer quite easily.











This is doing the spaybar parts for the Eta engines- the image makes the thread look truncated but it's not. The wire is just ground at a shallow taper - it's important to constantly withdraw to clear the swarf away as it will soon become crowded and possibly jam. Here are the finished parts. The threaded needle is done by drilling through a 7BA bolt and loctiting on the needle





1/16 Music wire should fit a 1/16 hole if it's very slightly over size but size for size is usually interference. Doing the same thing will ease it but the edges do need to be sharp as only a scrape is coming off.

Hope that helps - Tug


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## Tim Wescott (Apr 30, 2021)

Edit: I just realized I responded to an old post.  Oh well -- I'm leaving this.  Pretty drawing and all that.

If you don't introduce too many errors in deburring, there's a way.  Edge-find the exhaust ring, and move in a known offset from that.

An even better way, if you have three or four hands, would be to put a bit of drill rod of a known diameter into the corner between the exhaust ring and the outer cylinder wall, and edge-find off of _that_.

This all means that the precision of your transfer ports is dependent on the precision of the location of that exhaust ring and the thickness of the cylinder wall, both of which did not used to be controlling dimensions.

But, hey -- driven by needs and all that.


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## pat_pending (Apr 30, 2021)

Ramon said:


> Pat, Though either will do there is a distinct difference between 'Music wire' and 'Piano' wire not least that the music comes in imperial sizes and piano in SWG.  Piano wire is much harder and springier than music. Most wire sold in model shops from the KS range is music wire and usually has a small label attached to each piece saying so
> 
> 16 SWG piano wire is just over a 1/16 so won't go into a 1/16 hole unless it drills oversize. A piece of it however can be turned into a reamer quite easily.
> 
> ...


Thanks Tug. Yes I'm studying you ETA and Super Tigre builds v carefully!   .

Any tips on the D-Bit? I guess grinding the width with a Dremel Danger Wheel or bench grinder a 'smidge' under half seems to be the common wisdom and then trying to get a decent finish/sharp edges with a stone?

Thanks,
Patrick


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## pat_pending (Apr 30, 2021)

Thanks for the ideas Tim. I have 4 hands so will try the suggestion with the drill rod. Time to brush up on me Trigonometry!... It's been a while!   

-Patrick


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## Ramon (Apr 30, 2021)

Its not a D bit Pat merely a flat acute angle ground across the wire by holding the wire at such an angle on the side of a wheel - try not to get it too hot as you'll lose the temper. If you can't hold it long enough to get a flat area then clamp it to something that will prevent the wire turning.

Tims idea is how I went about it but without edgefinder just used the cutter but the more I think about it the more I can see the ease of the scribed line technique. Providing the line is fine and accurately placed relative to the top edge of the exhaust port for maximum efffect and the needle point runs true the accuracy is probably as good as you would want.

Tug


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## pat_pending (May 2, 2021)

Hi all,

bit more shed time today and managed to get the NVAs done. A seemingly easy set of operations with surprisingly many opportunities to cock things up especially on the final operations. My nerves are shot and I'm going to have a beer. I'm happy-ish with the result and Im pretty sure they'll work fine as they are airtight, needle seat is just a smidge under the hole and the places where the needle goes were reamed with the same music wire so no air bypass there.

That reamer made from the music wire worked an absolute treat and was a joy to use. It cut beautifully and pulled out layers of brass swarf that looked like a Vienetta ice cream. yum.

Where I would probably improve things next time is how far the thread goes up the spray bar up to the venturi. The die (obviously) didn't cut a thread to the very edge so I'll need to make a small washer to take up the gap. Not a 'biggie' but far from perfect.

I also seemed to bend one of the spray bars a tiny bit whilst cutting the thread (or being clumsy doing something else). I think that one will be a bugger to turn the thimble as the tolerances between the needle and the bar are so tight. That's in the spares/engine #3 bin for now and I might remake it but need a break from the tiny brass parts for now! The other two are spot on.

Axial accuracy on the lathe is one of my weaknesses also atm. I could really use a DRO. Wheeling that cross-slide and counting at 0.025mm per tick is tiring over longer distances!

Anyway here are some pics. I'm down to the 'hot-end' now (liners, pistons and contras). Tomorrow i will try to finalise the cutters and hopefully get the cylinder blanks turned. Exciting to be approaching the finishing straight although the risk of some mistake made earlier scuppering plans is very real as always.

Thanks,

Patrick


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## pat_pending (May 4, 2021)

Just as I was getting a bit of a 'pace on', disaster struck. The headstock bearings in my trusty Sieg SC6 decided to pack up on me. I noticed more vibration/noise than normal and the case was getting a bit warmer. I thought i'd be able to limp through these Vipers and do a strip-down after but things were too bad and deteriorating rapidly. Turning the chuck by hand, it felt like the shaft was square! I took off the belt and tensioner to see if the problem was there but no such luck. In the end it was the back bearing that had died and not the front angular contact beading which still seemed OK. With al the grief of the strip-down I decided to replace them both. I was on my own in terms of how to do this job so will probably post an Instructables or something (provided I'm successful) for anyone attempting similar.

For those interested to see, look at the surface finish on that cylinder liner I had just started on. The part will be easily salvageable at the lapping stage but a strange pattern on the surface I've definitely never seen before.

Good progress today and home-made puller did the job. The replacement bearings are on order from Simply Bearings and hopefully not too many snags at the point of pressing the bearings back in.

On the bright side, i should have a super smooth running machine replacing the Chinese 'car grade' bearings to Timkin and SKF.

Thanks,
P


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## Tim Wescott (May 4, 2021)

So, is a claw hammer an approved machinist's tool?


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## pat_pending (May 4, 2021)

Tim Wescott said:


> So, is a claw hammer an approved machinist's tool?


One man's claw hammer and cat litter tray is another man's drift and parts washer  .

I found some perfect size tubing in my scrap bin to tap out the bearings after using 3 bolts and some shims as a puller as below. When the work started getting more manual, i layered up on the lathe way protection. Worked out very well indeed. Sometimes the outer race of the angular contact bearings can be a pig to get out!

P


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## Billitmotors (May 5, 2021)

pat_pending said:


> Hi Billit, that also sounds like a neat option. What sort of edge did you put on the HSS Bit for this to cut nicely? I might also give this a try.
> 
> Thanks for the tip.
> 
> P


Gday Pat
if you imagine a very short HSS parting tool with an increased front clearance so that the heel of the cutter does not rub, and minimum side clearance on both sides. I will find my cutter on the weekend and take a photo and post it here.  When cutting the ports I I fed it in slowly and gently by hand and it worked just fine.


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## stanstocker (May 5, 2021)

Tim Wescott said:


> So, is a claw hammer an approved machinist's tool?


Heck Tim,
Carefully remove, drift out, press out, beat the sucker into submission, wail on that pig.  It's all just a matter of words 

Looks like a well battered piece of wood was used between the hammer and the work, so a 16 ounce claw hammer or a 16 ounce ball pein, all the same.


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## 777engman (May 6, 2021)

Hey pat, just wondering why you didn't just purchase a suitable woodruf cutter for doing the ports? Or have I missed something?
Dean


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## 777engman (May 6, 2021)

Also good luck with fixing the lathe mate hope it all goes well, I did a full strip down and rebuild on my raglan 5" over lock down last year, those head stock bearings were a bit of a job so I feel your pain with that one mate.
Dean


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## 777engman (May 6, 2021)

pat_pending said:


> Thanks Dean. Ideally I’d like to be a bit further away from the cutter for sure. I’m sure it’s obvious but you don’t happen to have a pic/description of your process/fixtures ? That would really help.
> Patrick


I'll upload photos soonish, just a bit tied up at the moment


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## pat_pending (May 7, 2021)

stanstocker said:


> Heck Tim,
> Carefully remove, drift out, press out, beat the sucker into submission, wail on that pig.  It's all just a matter of words
> 
> Looks like a well battered piece of wood was used between the hammer and the work, so a 16 ounce claw hammer or a 16 ounce ball pein, all the same.


hah. Yeah and that approach didn't work anyway. I had to use the bolts as a puller. Made another puller out of 3 bits of M12 threaded rod and a scrap bit of 3.2mm walled 50mm mild steel box section and that worked a charm.


----------



## pat_pending (May 7, 2021)

777engman said:


> Also good luck with fixing the lathe mate hope it all goes well, I did a full strip down and rebuild on my raglan 5" over lock down last year, those head stock bearings were a bit of a job so I feel your pain with that one mate.
> Dean


Thanks. So far so good. Waiting for a separator to arrive from eBay to allow me to remove the tapered roller bearing inner from the shaft. I had the Dremel 'wheel of destruction' in my hand to cut it off but managed to put it down and wait for the proper tool to arrive   

P


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## pat_pending (May 7, 2021)

777engman said:


> Hey pat, just wondering why you didn't just purchase a suitable woodruf cutter for doing the ports? Or have I missed something?
> Dean


I would have loved to! Although learning a new skill is always cool. I searched far and wide and nothing came up 3/32 x 1". There were companies making them to order for £120 and some available in the US which, when you add shipping, comes to about the same. If anyone knows where i could find such a cutter that would be really helpful (although I have cut another two blanks to try some variations on the geometry to see if i can improve on the last ont that already works pretty well).


----------



## xpylonracer (May 7, 2021)

That's what model making is all about IMO, makes a change to make some tooling and gives great satisfaction when it works as intended. As said good quality tooling is expensive and the cheaper tooling may not be accurate or of a quality to do all the cuts needed.


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## Tim Wescott (May 7, 2021)

I got curious and looked.  I didn't find any either -- you could maybe take a 1" diameter, thicker cutter and grind it thinner, but the shank might get in the way, and you'd need a toolpost grinder or a really dab hand at a bench grinder.  Or, there seems to be a good selection of 1" diameter slitting saws.  I didn't see any 3/32" saws on MSC Direct, but you could either stack a 1/16" with a 1/32" (I don't know how much of a Machinist's Sin that is), or you could take two cuts with a 1/16" saw for a 3/32" wide slot.


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## pat_pending (May 8, 2021)

Tim Wescott said:


> I got curious and looked.  I didn't find any either -- you could maybe take a 1" diameter, thicker cutter and grind it thinner, but the shank might get in the way, and you'd need a toolpost grinder or a really dab hand at a bench grinder.  Or, there seems to be a good selection of 1" diameter slitting saws.  I didn't see any 3/32" saws on MSC Direct, but you could either stack a 1/16" with a 1/32" (I don't know how much of a Machinist's Sin that is), or you could take two cuts with a 1/16" saw for a 3/32" wide slot.


Yeah I really *did* have a good look about. My other thought was that the width of the cutter is critical here with respect to position of the top of the port but probably not the diameter. I was thinking you could probably get away with a slightly smaller diameter and adjust the port width through the depth of the plunge cut. I'd be reluctant to go with a larger diameter cutter as the edge of the port might get too thin/glow red when running/cause a raft of other issues.

It was at this point that I rolled up my sleeves and started trying to make my own cutters. I have some HSS round bar coming soon also so will give the boring bar/fly cutting technique a try.


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## pat_pending (May 8, 2021)

OK, I'm back in business. The headstock bearings have been done and, my word, what a difference that made. It's like a completely different machine. I'm really looking forward to getting going on those cylinder liners on Monday.

I posted the nitty-gritty of the bearing replacement on a separate thread if anyone is interested it's here.






						Sieg SC6 headstock bearing replacement
					

Hi,  I just finished replacing the headstock bearings on my Sieg SC6 lathe and I thought I'd share how I did it incase it helps anyone else out there. Sieg lathes are the classic 'Chinese mini-lathe' so may well sell under different names / colours worldwide (Grizzly I think in the US?). Anyway...




					www.homemodelenginemachinist.com
				




So in the end I'm measuring 0.007mm runout measured in the spindle taper and a tailstock alignment of 0.003mm over 60cm. Probably the best I'm going to get on that machine. I reckon I'm good to go.

P


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## Billitmotors (May 9, 2021)

Billitmotors said:


> Gday Pat
> if you imagine a very short HSS parting tool with an increased front clearance so that the heel of the cutter does not rub, and minimum side clearance on both sides. I will find my cutter on the weekend and take a photo and post it here.  When cutting the ports I I fed it in slowly and gently by hand and it worked just fine.



G’day Pat here are some photo’s of the tool that I made to cut the exhaust ports on my Naylon Vipers as well as one of the one of the spare cylinders I made


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## Billitmotors (May 9, 2021)

Billitmotors said:


> G’day Pat here are some photo’s of the tool that I made to cut the exhaust ports on my Naylon Vipers as well as one of the one of the spare cylinders I made


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## xpylonracer (May 9, 2021)

That's much simpler to make than a multi-tooth cutter and as long as it does the job a very good alternative.


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## pat_pending (May 10, 2021)

Thanks Billit. I'm going to give that a try too. Cheers for the photos.

P


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## pat_pending (May 11, 2021)

Perhaps jumping the gun a bit here and at the risk of opening up an old debate, could someone recommend a prop for running in these Vipers? I used a 9x5 on the Boll Aero which it turned 6.5K RPM and now understand was probably a bit too much 'work' for it. I've seen people talk about 8x4 on a bunch of the forum threads only I cant seem to find props of that size anywhere in the U.K (other than funny-shaped plastic ones for drones/quadcopters). Anyone in the U.K with a source would be greatly appreciated.

Thanks,

P


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## sniffipn (May 11, 2021)

pat_pending said:


> Perhaps jumping the gun a bit here and at the risk of opening up an old debate, could someone recommend a prop for running in these Vipers? I used a 9x5 on the Boll Aero which it turned 6.5K RPM and now understand was probably a bit too much 'work' for it. I've seen people talk about 8x4 on a bunch of the forum threads only I cant seem to find props of that size anywhere in the U.K (other than funny-shaped plastic ones for drones/quadcopters). Anyone in the U.K with a source would be greatly appreciated.
> 
> Thanks,
> 
> P


8 x 4 IC by APC


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## pat_pending (May 11, 2021)

sniffipn said:


> 8 x 4 IC by APC


Thanks. Have ordered a couple. P


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## pat_pending (May 12, 2021)

Afternoon all. I managed to stick my head in the shed a bit this morning and put my mind to those pesky cylinder liners. Rather than ruin 4 blanks I thought I'd take a pause after the first to see if I've made any obvious gotchas. I'm quite happy with the result but the inside of the liner is full of burs as expected. I'll need to get some quality time with the needle file and magnifying glass to remove the worst before lapping.






The drilling operation was a bit iffy. The undersized slot drill (2.5mm)  seated nicely after starting v, v gently but following with the specified #33 jobber drill didn't feel right until the last mm of the plunge or so. I will have a look whether such a thing as a #33 slot drill exists as this would allow me to do the operation in one and possibly lave a nicer hole.

I also made a new cutter this morning with 'backed-off' teeth. This seemed to cut OK-ish but I still have a few problems preventing t from cutting cleanly which I will try to remedy before making liner #2. I have some ideas.

Anyway here's how it went.

The new cutter before hardening.






Turn down the bottom of the liner and check fit with the crank case. Bore out as smooth as possible to save time with the lapping later. I took a lot of care to get the dimensions spot-on here as i would be using this as the reference surface for the ports.






Expanding mandrel #4 ... getting a lot quicker at making em. I realised I should have made a box of M6 and M5 tapered screws in batch when I last had the lathe set up to use in the future.







Mount on mandrel and finish the outside and final length of the liner.






4 blanks ready for action.






Scribe the line for the start of the transfer port drill hole.





Mount in rotary table and cut the exhaust ports.






Set the head of the mill over at 25deg and drill the transfer port hole. I located on the line with the needle point attachment from my wiggler set


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## Ramon (May 12, 2021)

Pat - looking at your image of the cutter- 'draw a line' from the gullet of the tooth bottom left hand side to the gullet of the tooth above.  I would think you need to remove the land out side of that line on each tooth (both sides) as I would guess that's possibly rubbing at depth.

As said before - a sacrificial, tight fitting, aluminium plug inside the bore will help minimise 'break through' burring inside the bore - just tap the plug out after machining.

Looking good - certainly sold on the idea of the scribed line set up.

BTW following a discussion on a control line forum be aware that the Kavan _flexible_ yellow nylon 8x6 props have been known to shed a blade and particularly so on diesels. Not happened to me but I pass that on in the interests of safety - not only to your self but to the engine too!

You'll be fine with the APC though but do lightly sand the rough edges of the blades before use - particularly the TE as they are as sharp and hard as a razor otherwise. Believe me, skin _always_ loses 

Tug


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## pat_pending (May 13, 2021)

Ramon said:


> Pat - looking at your image of the cutter- 'draw a line' from the gullet of the tooth bottom left hand side to the gullet of the tooth above.  I would think you need to remove the land out side of that line on each tooth (both sides) as I would guess that's possibly rubbing at depth.
> 
> As said before - a sacrificial, tight fitting, aluminium plug inside the bore will help minimise 'break through' burring inside the bore - just tap the plug out after machining.
> 
> ...


Thanks Tug. To make sure I understand correctly, i should continue the filing right to the bottom of the gulley shown in the red line here and bring it right up to the edge (blue line) removing that land?


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## pat_pending (May 13, 2021)

Hi my 8mm HSS round blank arrived yesterday, I will have a go at the approach you suggested too. I'm a bit rubbish at shaping HSS tools and don't even have a grinding rest yet so this might be a bit of fun 

Thanks,
P


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## Ramon (May 13, 2021)

'Morning Pat,

The teeth only need enough clearance to achieve the depth of cut desired. Also bear in mind it's only the very tip of the teeth that define the cut dimensions so anything behind is potentially rubbing. This will be even more important with your single point cutter if you go that way. It's always best for finish and dimension to ensure the cutter behind the cutting edge has clearance.  About the only commercial cutter that features straight sides and no clearance that I can think of is a woodruff cutter which has a ground flat surface either side. Unfortunately these can't be used because of their large (relative to cutter dia) shank diameter and very short minor shank length

Hope that helps - Tug


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## pat_pending (May 13, 2021)

Ramon said:


> Pat - looking at your image of the cutter- 'draw a line' from the gullet of the tooth bottom left hand side to the gullet of the tooth above.  I would think you need to remove the land out side of that line on each tooth (both sides) as I would guess that's possibly rubbing at depth.
> 
> As said before - a sacrificial, tight fitting, aluminium plug inside the bore will help minimise 'break through' burring inside the bore - just tap the plug out after machining.
> 
> ...


Thanks on the advice RE props. Incidentally, i went down a Youtube 'rabbit-hole' the other day looking at control line speed flying championships. Fascinating stuff. Turns out that the fastest flyers only have one wing and one propeller blade and go 200+ MPH! I suspect a specially designed setup vs a blade firing off unexpectedly at 13,000 RPM are very different propositions .

P


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## Ramon (May 13, 2021)

Pat - You would be right but don't dismiss that info lightly. Have a look here Barton Model Flying Club :: View topic - Nylon Props - post 6 is from someone I have known for many years - a seasoned, very knowlegeable and highly experienced aeromodeller. The potential is there with these specific props - not necessarilly _will_ but _might_ - if it does then personal safety and that of the engine/model is of concern. I tend to work on the basis that if you don't use them the problem doesn't exist  

BTW If you really want to see an engine working (maybe that should be hear!) at it's best try You Tube - 'tethered model car championships'


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## xpylonracer (May 13, 2021)

Same problem with Topflite white nylon props many years ago, advice slip with each box was to keep the props in damp atmosphere because the problem arises when the nylon dries out, whether that advice still stands today I don't know.

Marcus


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## pat_pending (May 13, 2021)

OK, 4th and final attempt on the cutter today. I think the result is quite decent (by my dodgy surface finish standards anyway) and the cut seems much less violent on the part. I reckon tomorrow I will make some tight-fitting plugs as suggested by Tug, touch-up the cutter with a stone and go for the 3 other liners  . I will try the boring bar method once I have sorted out a grinding rest but have the HSS bar and boring head on standby ready to go.

So this time round I remade the arbor to solve the ridiculous runout issue I had before. I made a register on the arbor thats a tight fit with the cutter hole rather than relying on the bolt for anything other than pulling force. I had another go at 'backing-off' the teeth and think the results are far better. Might give the teeth one more lick with the diamond file tomorrow before I crack on.

Anyway, here are a couple of pics of the new cutter for those insomnia sufferers out there 

New arbor with a register for the hole in the cutter






I took a tiny skim to make sure all teeth were the same length taking out any runout vs the hole (only reduced the diameter by 0.05mm or so)








Backing off the teeth. I went as close as I could without touching the tooth behind. Engineers blue (uh-herm, blue marker) was useful to see when you get to the edge.














Profile view. Perhaps I went a bit extreme with the backing-off!







Hardened and sharpened. I will do a bit of a touch up on the sharpening tomorrow before I attach those liners as that one tooth looks a bit blunt!








It seems to cut OK and with a lot less effort than before and there are less 'lines' on either the bottom of the cut or the sides.







Again, nice little rolls of swarf and no little crumbs. .


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## pat_pending (May 13, 2021)

Ramon said:


> Pat - You would be right but don't dismiss that info lightly. Have a look here Barton Model Flying Club :: View topic - Nylon Props - post 6 is from someone I have known for many years - a seasoned, very knowlegeable and highly experienced aeromodeller. The potential is there with these specific props - not necessarilly _will_ but _might_ - if it does then personal safety and that of the engine/model is of concern. I tend to work on the basis that if you don't use them the problem doesn't exist
> 
> BTW If you really want to see an engine working (maybe that should be hear!) at it's best try You Tube - 'tethered model car championships'


Scary stuff with the Nylon props! I reckon I'll stay away. I like the look (and less sharpness) of wood props for bench running but the sizes are much more limited. 

The tether car stuff is cool also. Perhaps i could hone my TIG-welding skills to make a tuned pipe one day


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## pat_pending (May 14, 2021)

Hi all. I took the plunge today and went for those cylinder liners. I was nervous about destroying the blanks, newly made cutter and the only 2.5mm 4-flute endmill I own so I took things really really slowly. I think the result is pretty decent and I'm sure the holes are accurate to within a metric whisker.

Still a little bit of de-burring to be done as you can see but the trick with the tight-fitting aluminium plug really worked a treat to reduce the burrs on the inside of the liner where they would be the most difficult to remove or whey they are most likely to ruin the lap.

Right I think I'm onto lapping and then cast Iron bits. Annoyingly, I have run out of aluminium bar so need to get my hands on some before I can make a lap! I have ordered a few from Noggin End so should be there in a couple of days, 

Im really excited to be on the finishing straight now!

Thanks,
P







a couple of pics from making them.

Height set from bottom of the liner seat using cigarette paper. I marked the widest tooth with red marker as a couple had been touched with the file during backing off. Overall width still good to within 0.02mm







Cut the port using lots of cutting, a slow speed (220RPM) and enough feed so that chips were coming out and not crumbs.






Use the needle centre-finder to precisely hit the scribed line for the start of the transfer port hole with the mill head set to 25deg.






Use an undersized 4 flute endmill (2.5mm in this case for a #33 drill which is 2.89mm). High RPM and peck drill with a really gentle pressure particularly before the cutter was completely seated in the hole.






Finally follow the 2.5mm endmill hole with the #33 drill. This didn't feel nice as the drill was bouncing around until fully in the hole. I reckon going all the way with a #33 sized endmill (if that exists). I was toying with the idea of using a readily available 3mm endmill bt it was too late to adjust the plans so i stuck with it.


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## pat_pending (May 14, 2021)

Billitmotors said:


> Gday Pat
> I usually use teflon for my gudgeon pin end caps.


Hey Billit. Any tips on the gudgeon pin caps? Do the caps actually fit into a drilled gudgeon pin or are they just plugs at the end of the hole in the piston using a shorter pin?

Patrick


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## pat_pending (May 21, 2021)

Got a bit of time over the past couple of days to work on the viper. I managed to get the pistons lapped and tapered, made the pistons and wrist/gudgeon pins. I think from here on in I will shift to one engine at a time as my patience is like a kid before Christmas and i have an oily/smoky workshop firmly in my sights!

Quite a collection of bits now. Engines 1 + 2 will be complete. Engine 3 I will do at some point in the future (or one of the engines explodes in which case I have spares).






Lapping using a simple aluminium expanding lap as I did with success on the Boll Aeros. Started with 320 grit carbide grinding paste then went to 600. I will finish off with 1000 on the final piston/cylinder fitting.






Liners all done. Really happy with the finish although the photo doesn't really show much.






The operation for making the pistons was to turn the bottom end and bore out the insides first, cross drill (undersize 3.8mm for a 4mm final reaming for a push fit onto the gudgeon pin), then mount on the mandrel shown below to turn to final outer dimensions.






The viper has this unusual piston 'crown' at 55 degrees. I was gong to ditch it and go for a flat piston but lost the nerve thinking how i'd need to adjust the other thins to keep the port timing right. I will try this on engine #3 when I get round to it.











Gudgeon pins were made of silver steel and polished with 1000 grade wet-n-dry paper. i took care to make the ends as smooth as possible to avoid scoring the cylinder. They will be a tight push fit so hopefully there will be no 'floating' going on in any case.







So now onto more lapping... I can smell the castor oil already!! I turned the pistons 0.1mm oversize which, with more confidence machining, I can drop down to something less next time. The lapping is going to take AGES! I'm on the 320 grit again and just as the piston (not the crown) starts entering the bore I will switch to 600 and 1000 for that last little bit around the exhaust port.






Thanks, 
Patrick


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## Tim Wescott (May 21, 2021)

That 55-degree "crown" looks like could be there to help scavenging, by guiding the puff of fuel/air from the transfer ports to the top of the cylinder.  Flat-topping the piston, even after adjustments for proper timing, may not give good results.


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## pat_pending (May 22, 2021)

Tim Wescott said:


> That 55-degree "crown" looks like could be there to help scavenging, by guiding the puff of fuel/air from the transfer ports to the top of the cylinder.  Flat-topping the piston, even after adjustments for proper timing, may not give good results.


Hi Tim. Yeah that's what I figured in the end. I was a bit worried about the lapping with a chamfered bit on the top of the piston but it turned out to be exactly the same as for a flat piston.


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## pat_pending (May 22, 2021)

Hi All,

some good progress with the lapping on engine #1 today and the liner + piston are a great fit. I need to make the contra-piston now and I'm ready to move on to the FFFA phase (Final Fettling Filing and Assembly). I took care on all fits so this should not be too much of a job. Hopefully by tomorrow we'll get some puffs of smoke at least.

I have 2 quick questions for the seasoned engine builders out there if I may.

1) For a 'tight push fit' on the gudgeon pin in the piston i have been relying on the taper of a hand reamer and coming in very gradually from one side until the pin wedges in the other (so far so good). I was wondering how tight a push fit this should be? (a) thumb tight (b) tap with a mini hammer tight (c) gentle arbor press fit. Apologies, I'm not an engineeer and these might have more specific names.

2) Im thinking of drilling some 1mm oil holes in both ends of the conrods to help with lubrication. Would these be preferable on one side for the direction of travel of the crank / stroke or is at the bottom OK?

Thanks in advance.

Patrick


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## pat_pending (May 26, 2021)

Hi all, good progress on the lapping then a bit of a setback. I had the engine assembled and victory was firmly in sight.






It was firing nicely on primer but would never catch and run. The mystery here was that, as opposed to the last engine, this one was really airtight. I put soapy water all around the crank case and not a single bubble blown anywhere. Furthermore, fuel would be sucked up the tube when covering up the carb choke.

After I could hardly move my arm after all the propeller flicking (no exaggeration) and I got hit in the finger half-dozen times by the prop, I went back to the plans and did a lot of head scratching (and being generally in a sh**ty mood).

Turns out I missed a detail in the plans which means the transfer ports CAN'T WORK. So obvious in hindsight and bloody annoying!!

I missed the recess in the top of the crankcase.

My engine below. No passage from the crank to the transfer ports.






The plans have this rather delicate cutout so the transfer passage runs behind the liner.






I have two options now to save the engine.

1) Mount up the crankcase on the 4-jaw indicated on the bore and turn a recess using some sort of boring/internal grooving tool.
2) Go 'off-piste' and modify the cylinder liner to have a channel that connects to the crank case.

Both are equally risky in terms of wasted time to re-make the part if it doesn't work out as the lapped liner/piston and contra combo took 2 days at least. Out of the two operations, mounting the liner in the rotary table and extending the transfer passage is probably easier. 

I will sleep on it and it will be decided by morning. Lesson learned here RE looking at plans properly. I had this niggling feeling that something wasn't right as i couldn't understand how the design was supposed to work and should have stuck to my gut instinct.

Not too much of a detour and the engine felt and sounded lovely on those few seconds running on primer so very excited to bring them to life soon.

Thanks,
P


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## Peter Twissell (May 26, 2021)

If it were me, I would definitely go for the crankcase modification.
The space you need to create in the crankcase is far less critical than the risk of distorting the cylinder.


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## Jasonb (May 26, 2021)

Should be easy enough with a standard boring bar, set the topslide/compound over 25deg and use that to feed in for the tapered part and then the carriage to carry the cut on down to meet the crank bore


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## Ramon (May 26, 2021)

Pat
Boring out the crankcase to give a transfer passage as the original design is probably 'overkill' for what is actually needed. It will certainly lead to an excess increase in crankcase volume. As an alternative passages can be cut into the side of the case bore using an homemade cutter that match the position of the passages in the liner...

This shows it being done on the Oliver Tigers - the cutter having been used on previous engine builds





What ever way you do it stop the taper below the top face and not bring it to a knife edge as shown - you can see what I mean better here.





If you bore it to a knife edge and you overshoot slightly you stand to lose the liner locating diameter as well as potentially affecting the seal.

As I see it, whilst passages need to be big enough there is a point where transfer passage volume becomes too much and crankcase volume (and pressure) suffers as a result.

Tug

PS Another alternative would be to modify your liner as you suggest - these are the Eta Liners but the volume on their own is marginal - the cases still have passages in them as above


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## pat_pending (May 27, 2021)

Ramon said:


> Pat
> Boring out the crankcase to give a transfer passage as the original design is probably 'overkill' for what is actually needed. It will certainly lead to an excess increase in crankcase volume. As an alternative passages can be cut into the side of the case bore using an homemade cutter that match the position of the passages in the liner...
> 
> This shows it being done on the Oliver Tigers - the cutter having been used on previous engine builds
> ...


Thanks for the advice Tug. That makes a lot of sense. I still have a bit of trouble getting my head around the cutter profiles. You don't happen to have any  pics of making them do you? I don't recall seeing it on the Super Tigre thread.


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## pat_pending (May 27, 2021)

SUCCESS!! 

Thanks to all the great advice from you guys, my engine #1 runs. Lots of room for improvement (especially as this was the one made from all the blemished/less than perfect bits).

Chuffed to bits! (but a bit lightheaded from breathing in those fumes. I should really run these outdoors.

I am following this guide on running in from the Adrian's model aero site.



			AdriansModelAeroEngines.com :: Classic Model Diesel/Glow Break-in
		


I have the first 4 minute ultra-rich run with the 9x5 on low compression (missfiring) under the belt and will switch to the 8x4 for the short hot runs.

again, thanks everyone!

perma-grin Patrick


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## Ramon (May 27, 2021)

Congratulations Pat - well done on acheiving a good runner  Been pleased to help and answer all those questions. You've got what it takes now (or should have ) so hope your future builds meet with similar success.

Re cutter making heres the above cutter being made for the Eta engines




















The cutter was plunged in sideways to depth then the passage cut 'upwards'

Hope that helps - Tug


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## pat_pending (May 27, 2021)

Ramon said:


> Congratulations Pat - well done on acheiving a good runner  Been pleased to help and answer all those questions. You've got what it takes now (or should have ) so hope your future builds meet with similar success.
> 
> Re cutter making heres the above cutter being made for the Eta engines
> 
> ...


Thanks Tug. I’m dying to try one of these. Will report back. Also  do a video of running engine once I’m through the excitement of playing with it. 

P


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## pat_pending (May 31, 2021)

Hi, I haven't reported back as I've been having too much time playing with the engine .

Here she is running an 8x4 prop after a few running in-runs. RPM there was about 11K but that wasn't fully 'leaned-out'.



I will turn my attention to the other Viper and seeing if I can't improve on how she 'breathes' by using the transfer passages Tug suggests. 

I couldn't be happier. Thanks again all for the help.

Patrick


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## Mechanicboy (May 31, 2021)

Patrick. Well made to run the model engine, but I spotted the propeller is in wrong side. Is it right the propeller is in wrong side?


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## pat_pending (May 31, 2021)

Mechanicboy said:


> Patrick. Well made to run the model engine, but I spotted the propeller is in wrong side. Is it right the propeller is in wrong side?


hi mate, I’m pretty sure it was pulling rather than pushing. I’ll double-check next run. Don’t want anything overheating! I’m just about to switch over to some larger props and cooler runs from now on in. P


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## Ramon (May 31, 2021)

Hi Pat

Nice run but I too had to look at the prop hard to see if it was back to front. I found it difficult to determine as it does look as if you have it that way. Turning the prop such does not turn it into a 'pusher' BTW    Turning the prop around was a recommended way to reduce the thrust on free flight models in the early stages of trimming.

Easiest way to tell is the leading edge is more rounded and thicker than the trailing edge - what make of prop is it?

Surprising how much you have to make to make an engine eh?

Don't over load the engine with excess diameter (or pitch) - a 9 x 4 should be ideal for further running

It will be interesting to compare the different results with differing transfer passage volumes

Tug


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## pat_pending (May 31, 2021)

Ramon said:


> Hi Pat
> 
> Nice run but I too had to look at the prop hard to see if it was back to front. I found it difficult to determine as it does look as if you have it that way. Turning the prop such does not turn it into a 'pusher' BTW    Turning the prop around was a recommended way to reduce the thrust on free flight models in the early stages of trimming.
> 
> ...


You are both right (of course)  I thought the ‘sharp end’ would be better at cutting through the air so made that the leading edge... and of course the more rounded end better for not cutting my fingers on the ‘flick’ especially in the event of flooding the engine. every day is a learning opportunity.

The make of prop is APC and they seem to have most sizes available. 9x4 on order.

RE the bits you have to make to make an engine: I think that they are roughly equal! I reckon I’ll get a load of reuse though especially if I continue on the 2.5cc path. The scrap bucket should go down too.... who knows


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## pat_pending (May 31, 2021)

Also, forgot to ask, any tips on balancing props? Drilling out the centre here to fit the Nalon  prop nut to 7.5mm might have added 0.5mm runout! I was thinking of mounting in the lathe on some sort of arbor and taking light skims off the end of the blades at a high RPM and sharp tool. Thinking there might be some better way


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## Ramon (May 31, 2021)

APC props are very efficient in use - they are also extremely efficient slicing through flesh as quickly as a scalpel either as you percieve, running your finger down the edge as you flick a flooded engine or if you catch your fingers in the prop arc. Believe me you will not be the first  

I always sand both edges of new props to take that sharp mould line off - particularly so the trailing edge for that very reason. Only recently I sliced into my right index finger near down to the bone on a friends untreated prop so always treat any moulded prop and particularly the glass filled nylon or carbon props with respect. I've never used a chicken stick nor one of those rubber finger protectors but I do use an old stout leather gardening glove. Regretably I was not wearing it at the time mentioned.

Probably a better general prop would be a Master or Graupner Standard though the latter do tend to be a bit on the heavy side.  Best of all for your purpose is wood but they are getting very difficult to find in the sub 10" diameter range.

Keeping to a specific size does help - there's quite a lot that can be recyled especially exp. mandrels and laps.

All the best with whatever you do in future Pat - you've persevered here and shown you have what it takes - so go right on and go for it

Tug


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## Ramon (May 31, 2021)

pat_pending said:


> Also, forgot to ask, any tips on balancing props? Drilling out the centre here to fit the Nalon  prop nut to 7.5mm might have added 0.5mm runout! I was thinking of mounting in the lathe on some sort of arbor and taking light skims off the end of the blades at a high RPM and sharp tool. Thinking there might be some better way




*Definitely don't do as you describe* - the blades would probably shatter.

You need to get your self a prop balancer or make a simple one - length of steel that fits the prop hub tightly. Cone each end of the steel to a sharp point about 60* inclusive

Insert through prop with equal amount protruding each side and support on the points between finger and thumb.

Sand the tip back on the heavier blade until near true then sand the back of the blade to fine tune.

There are several balancers available with very varying prices but in the end they all do the same thing. I have use the humble injection moulded one below from SLEC for years - still works for me.

Tug






__





						Search - prop balancer
					






					www.slecuk.com


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## Mechanicboy (Jun 1, 2021)

pat_pending said:


> Don’t want anything overheating!



Model diesel engine does not run hotter than glow plug engine and the engine is over lubricated (25-33% oil in fuel) that the oil conducts heat away from the engine and ensures that the engine runs well lubricated.


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## Rational Root (Jun 1, 2021)

Awesome. 

Now you need to build a plane around it 

David


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## pat_pending (Jun 1, 2021)

Rational Root said:


> Awesome.
> 
> Now you need to build a plane around it
> 
> David


Hey David, hope you're keeping well. Yeah, 'great minds think alike' and all that, I've got one of these on order:









						Original Flite Streak Kit
					

The original Flite Streak is an exact reproduction of the original version as George Aldrich produced it in the 1950's. This kit is part of the "Nostalgia Series" developed by Brodak.




					brodak.com
				




Patrick


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## Ramon (Jun 1, 2021)

Hey Pat - you never said you were a control line flyer - been a passion with me for over sixty years. Building a largish stunt model right at the momenmt - 'Coy Lady' - ring any bells?

If you want a similar looking but brilliant flyer get yourself a 'Frog' Talisman plan and get it scaled to 42" wingspan. I had one with an Olly in it - great combination.

Tug


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## pat_pending (Jun 1, 2021)

Ramon said:


> Hey Pat - you never said you were a control line flyer - been a passion with me for over sixty years. Building a largish stunt model right at the momenmt - 'Coy Lady' - ring any bells?
> 
> If you want a similar looking but brilliant flyer get yourself a 'Frog' Talisman plan and get it scaled to 42" wingspan. I had one with an Olly in it - great combination.
> 
> Tug


Hi Tug, I'm not currently but have always wanted to give it a go. I love the whole niche/vintage aspect to it too. Also, i get SOOOOO bored of me showing people engines only for them to look at me confused and say either "what are you going to power with it" or "couldn't you make an electric one"  and all that stuff  Im sure you know what I mean. This time I can say it's for a plane and cut the conversation short LoL.

Thanks for the tip on the Frog. I'll take a look. If there are any decent 'getting started' resources you could point me too that would be much appreciated.

Patrick


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## Ramon (Jun 1, 2021)

Well I hear your sentiment but if this is to be a first you really need someone to show you how to fly. Believe me it is not a matter of holding the handle and bending your wrist up to go up and down to go down. Everything from the point of launch will happen so fast you won't see it! If it follows true form the plane will go up, you will follow it with your arm (the worst thing you can do) and it will be over your head and into the ground before you can say Flite Streak.

I've shown a lot of people how to fly those first few laps over the years usually with success but you will have a pretty quick model there to begin on so theres quite a few things to keep in mind from building the model onwards. Time for that later. 

Buying a kit as you have is a costly exercise at the best of times - much better to buy a plan and some raw balsa.

Heres the link to the Talisman FROG TALISMAN PLANS CONTROL LINE PROFILE STUNT  | eBay - similar to the Flite streak in format there were several models of like designs.

Heres a standard 28" WS version I built a long time ago







But these are the kind of aircraft I prefer - aerobatic models of the 'classic' era (used to be '58 to '69) not sure what it is now





I still have the Thunderbird and the Nobler next to it. The other Nobler and Oriental were sold on and the Master was reduced to matchwood after a push rod failure - breaking them hurts!

Regards - Tug


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## pat_pending (Jun 3, 2021)

Beautiful planes Tug! I think I'll take it one step at a time and have reached out to my local model flying club for membership and to see if there's someone there who can show me the ropes/lines (excuse the pun).

I bought the flight streak off eBay with engine for £85 as a bit of an impulse buy. I think thats probably a good deal vs buying all the parts and making (or indeed a kit). I will look at the frog build if I get the 'bug'.

I'm going to take the plunge and try making those transfer passage cutters today and will report back.

Thanks,
Patrick


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## Circlip (Jun 3, 2021)

Worth a look for free downloads :-    Oz : Free plans : Collection of free vintage model aircraft plans to download

  Regards  Ian.


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## Tim Wescott (Jun 3, 2021)

I second the recommendation that you get help learning to fly.

Much as it pains me -- if you don't already have experience with engine handling, you should learn to fly on a plane with a factory engine.  The pool of people willing to help you with engine problems will shrink dramatically if you show up as a novice pilot _and_ you've built your own engine.  Unless there's someone in the club who seems to be a good pilot and is enthusiastic -- then go for it.


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## xpylonracer (Jun 4, 2021)

Pat
The best advice I received when starting to fly control line was with the control handle vertical with the "up" line at the top  lock the wrist at neutral and keep the arm straight, point your arm where you want the model to fly.

Marcus


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## Ramon (Jun 4, 2021)

Yep, that's the technique but there's a little more to add which I feel is best left until right before that first attempt.

Currently at the moment going through the moves with someone who last flew 50 years ago - so far so good    and just started inverted flying.

Tug


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## Tim Wescott (Jun 4, 2021)

If you're a courageous teacher, on the first few flights put the handle in your student's hand, then grab that assembly with _your_ hand and fly the plane through your student's hand.  When you feel they've got the hang of it, let go, lie down, and watch how they do.

If your hands aren't big enough for that, make a double handle so that you can both hold on.

Short-tanking the plane until the student doesn't get dizzy is a good idea, too.


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## Ramon (Jun 4, 2021)

Never quite thought of it that way Tim but looks like I might be a 'courageous teacher' Ha Ha !  

I've been doing it that way for years - young and old - but Pat's a fair distance away, I'll step in only if he can't find anyone locally which is what he really needs.

Of course he could always jump in his car and visit us for first hand treatment - we certainly won't be put off by the fact he has built his own engine  

Are you a regular  C/L flyer? Any preferences?

Tug


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## Tim Wescott (Jun 4, 2021)

"Are you a regular C/L flyer? Any preferences?"

I fly stunt in the US Pacific Northwest.  I'm not sure if you're familiar with the AMA events, but I fly in Expert.  I have been placing in the middle of the pack, but I'm currently working at a startup, and haven't practiced in a good long while.


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## Ramon (Jun 5, 2021)

Hi Tim, yes familiar with AMA stunt. Though lapsed now I was a PAMPA member for several years. My first Stunt News was a few pages just before Tom Morris turned it into the epic magazine it became. I no longer compete - last time was 2006 and am just getting back into C/L again after quite a long lay off. Sadly I let all my SN go.

Always had a predominent liking for the American designs especially of the Classic period. Yet to build my real desire -  a Tucker Special - but there's just about time left.  Currently building a British design 'Coy Lady' for a Stalker 40 an engine. I've had that for many years but it is yet unused. At 76 there's not much time left but what there is I intend to make the most of it.

Regards - Tug


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## pat_pending (Jun 6, 2021)

Thanks yet again for all the good advice guys. I'l certainly get tuition and use a commercial engine until I well and truly know what I'm doing!

Patrick


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## pat_pending (Jun 6, 2021)

Had a bit more shed time yesterday and completed Viper #2. This one seems to run a fraction stronger than the other one but only by a fraction.

Here is a video of her running after a few breaking in runs (propeller on the right way this time I hope  ). I have a solution for a finger-guard figured out involving 10 layers of duct tape too  



The only issue with this one is that the compression screw auto-unwinds it's self when the engine is over 11K RPM or so. The contra piston might be a fraction too loose a fit (although I thought it was really tight). The margin between too tight and too loose on these engines really is measured in 10's of atoms! 

Tug - I didn't get round to trying your transfer passage technique or use the fixture and cast iron you sent me to make the crankshaft. That will be the #3 Viper for which I have 60% of the parts in the box.

I start a new job tomorrow so it will be slow-going in the workshop for a while but super happy to get these two 'off the bench' before. 

Building these have been really fun. Starting to ponder the next challenge.

Taks care, 

Patrick


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## Mechanicboy (Jun 7, 2021)

pat_pending,.. bad idea to set the finger mid of the propeller blade. Set the finger near hub of the propeller and flip fast, it will make easier and safe to start the engine without cut the skin on the fingertip caused by the sharp propeller edge.


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## Ramon (Jun 7, 2021)

Good luck with your new job Pat and good luck with your future projects - maybe see you at one of the Old Warden events one of these days.

Been a pleasure to assist you - Tug


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## Billitmotors (Jun 8, 2021)

G’day Pat
Your Viper looks and sounds great. When you finish your second viper with with the different transferpassage method it would be interesting to see whether it gives any improvement to the performance.I have toyed with trying the other transfer passage method shown on the drawings.


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## pat_pending (Jun 8, 2021)

Billitmotors said:


> G’day Pat
> Your Viper looks and sounds great. When you finish your second viper with with the different transferpassage method it would be interesting to see whether it gives any improvement to the performance.I have toyed with trying the other transfer passage method shown on the drawings.


Hi Billit, yeah I’ll have a go at those when I get round to making the 3rd one and report back. I need to carve out some time to learn how to make those cutters.
Patrick


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## pat_pending (Jun 8, 2021)

Ramon said:


> Good luck with your new job Pat and good luck with your future projects - maybe see you at one of the Old Warden events one of these days.
> 
> Been a pleasure to assist you - Tug


Thanks Tug, I just looked up the Old Warden events that look great. Maybe I’ll try to get to the July one. I’ll DM you if I’m going!
Patrick


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