Nalon Viper 2.5cc CI Engine

[pat_pending]

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

 

[pat_pending]

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

 

[Ramon]

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

 

[pat_pending]

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

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

 

[xpylonracer]

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. ?

 

[pat_pending]

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

 

[pat_pending]

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

 

[Ramon]

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

 

[pat_pending]

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

 

[Ramon]

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.

 

[Billitmotors]

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.

 

[Ramon]

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

 

[pat_pending]

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]

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]

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

 

[Ramon]

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

 

[pat_pending]

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

 

[Ramon]

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!

 

[pat_pending]

Thanks for the

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!

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

 

[Ramon]

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