Nalon Viper 2.5cc CI Engine

[Tim Wescott]

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.

 

[pat_pending]

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

 

[pat_pending]

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

 

[Jasonb]

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]

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]

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]

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]

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]

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]

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]

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):

1. Square 3 blocks of stock 30X30X13.
2. Centre drill
3. Drill the venturi hole 6mm at x-8.46 y1.295 (left up)
4. Drill the 4 mounting screw holes at 3.3mm. 10.775mm from the centre
5. Mount in 4-jaw and centre on the register mark
6. Face to make sure everything is square
7. Drill the pin hole at 3.3mm
8. Countersink the pin hole 3.18 depth 5mm diameter
9. Tap the pin hole M4
10. Turn the register 4.5mm deep making sure to creep up on the crank cases to make an airtight fit.
11. Use hight gauge to mark 11.4 mm
12. Mount in mandrel and face to correct total length 11.4 mm
13. Turn down the pin retaining nut dimple 4.22mm
14. Mount in mill and centre on the venturi hole.
15. Countersink venturi hole 7mm to 5mm depth (I did 8 but this turned-out to be just too big)
16. 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.

 

[jetstuff]

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.

 

[pat_pending]

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

 

[Ramon]

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

 

[xpylonracer]

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

 

[Jasonb]

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

 

[Ramon]

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

 

[pat_pending]

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

 

[pat_pending]

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

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

 

[Ramon]

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