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Post by Roger on Jun 15, 2023 21:03:36 GMT
Hi Roger, Now I see what you mean! Yes, I guess that there is a route in though a gap and then backwards into the rings and into a port. However, it isn't much different from a normal ring and the gap is pretty tiny in any case. When I first finished them, they were immediately much better than previously. How much that was the new rings (the old ones were clupets too), and how much was the fact that I had reamed the valve liners to get rid of some corrosion/porosity, I don't know. However, now that they have run a few miles, the exhaust is really crisp again. Phew!! Chris. Hi Chris, It's a cracking job, and thanks for sharing the method of making them. I'm tempted to have a go making some PTFE ones, just for the hell of it. That might be something of a challenge, knowing how soft that material is though.
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Post by steamer5 on Jun 15, 2023 22:23:54 GMT
Hi Roger, At least it wouldn’t be heart stopping turning them inside out & then back again!
I wonder what the breakage rate was in the commercial manufacturing of these
Cheers Kerrin
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Post by Roger on Jun 16, 2023 7:58:49 GMT
Hi Roger, At least it wouldn’t be heart stopping turning them inside out & then back again! I wonder what the breakage rate was in the commercial manufacturing of these Cheers Kerrin Hi Kerrin, That's true, I imagine they broke a few. I'm not sure that you would even need to do that with PTFE ones. You could probably just crush the point where the joggle is. It may be possible to just slit them with a knife blade tool in the Lathe, turning it through part of a turn. Actually, you could probably slit a PTFE tube into a spiral with a knife blade tool in the Lathe as if screw cutting. That would leave the ends with an acute angle that would be vulnerable to damage. When you look at this, it makes sense as to why the Clupet ring is the shape that it is. I'm chewing over an idea where the whole cut could be made with a 0.5mm PCB cutter using the 4th axis on the mill in one operation. Actually, you could do that with a CI ring. Yes, it would have to be done very slowly and carefully, but that's the only issue as far as I can see.
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Post by steamer5 on Jun 16, 2023 8:08:59 GMT
Hi Roger, Hanging out for the video of you doing it on the 4th axis!…. Ok an edited version will do!
Cheers Kerrin
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uuu
Elder Statesman
your message here...
Posts: 2,811
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Post by uuu on Jun 16, 2023 8:26:53 GMT
With cast iron, and CNC/4th axis, might you be able to cut out the shape already inside out? So you'd only have one heart-stopping bending session after the heat treatment.
Wilf
PS - in fact you could do that with the PTFE ring, so it would close up when manipulated - since heat treatment not appropriate.
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SteveW
Elder Statesman
Posts: 1,397
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Post by SteveW on Jun 16, 2023 11:04:27 GMT
It occurs to ask how would you emulate in the necessary spring-out preload in a PTFE ring that gets generated by the CI ring's heat treatment cycle. Not forgetting the spring-together built in by inverting/reversing the ring prior to heat treatment.
I can understand how one might generated the spring-out in a simple PTFE ring. I think and I'm really guessing: either under pin it with an 'O' ring or machine it to bore size from a larger nearly closed 'C' section piece crushed to close the gap. Neither without issues.
Is it possible that Clupet rings are only really achievable using the right grade of cast iron and method.
Again guessing: I can see how multiple PTFE rings, maybe using offset pegging, could get very close to what the classic Clupet ring does.
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uuu
Elder Statesman
your message here...
Posts: 2,811
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Post by uuu on Jun 16, 2023 12:09:47 GMT
Perhaps an advantage of the Clupet design in a PTFE ring would be to accommodate the expansion of the material when heated. Designs discussed on this board often have the ring undersized when cold. (And, as you've guessed, have an o-ring underneath).
Wilf
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Post by Roger on Jun 16, 2023 15:57:14 GMT
With cast iron, and CNC/4th axis, might you be able to cut out the shape already inside out? So you'd only have one heart-stopping bending session after the heat treatment. Wilf PS - in fact you could do that with the PTFE ring, so it would close up when manipulated - since heat treatment not appropriate. I'm not sure that's possible. I think you'd still have to spring it that way.
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Post by Roger on Jun 16, 2023 16:03:49 GMT
It occurs to ask how would you emulate in the necessary spring-out preload in a PTFE ring that gets generated by the CI ring's heat treatment cycle. Not forgetting the spring-together built in by inverting/reversing the ring prior to heat treatment. I can understand how one might generated the spring-out in a simple PTFE ring. I think and I'm really guessing: either under pin it with an 'O' ring or machine it to bore size from a larger nearly closed 'C' section piece crushed to close the gap. Neither without issues. Is it possible that Clupet rings are only really achievable using the right grade of cast iron and method. Again guessing: I can see how multiple PTFE rings, maybe using offset pegging, could get very close to what the classic Clupet ring does. PTFE is so soft, that you can't really expect it to take on any springing as such. You could probably just crush the joggle in a vice enough to deform it without reversing the ring. You would definitely need an O-ring under the PTFE ring. That's necessary in my design which has four pegged rings in one groove, even though it's not used as part of the seal. Without it, there's nothing to spring the rings outwards. Two of the rings are side by side, with the gaps at 180 degrees. The other two rings are underneath those, with the gaps staggered so there's no gap uncovered axially or radially. PTFE expands a lot, so you need to have a large gap to accommodate it.
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Post by chris vine on Jun 16, 2023 22:13:46 GMT
For a helper spring under ptfe ring, or other synthetic material, how about a little strip of thin phosphor bronze which you could run between a pair of gears to that it ends up crinkly. Can't think of a better word. A turn of that could be be put under the working ring as a helper... Chris.
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Post by Roger on Jun 16, 2023 22:18:42 GMT
For a helper spring under ptfe ring, or other synthetic material, how about a little strip of thin phosphor bronze which you could run between a pair of gears to that it ends up crinkly. Can't think of a better word. A turn of that could be be put under the working ring as a helper... Chris. Hi Chris, You could, but I think it would probably be too strong. Silicone O-rings are really soft, so that might be a good option. You would probably only need around 10% compression of the section to do the job.
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abby
Statesman
Posts: 927
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Post by abby on Jun 21, 2023 23:39:16 GMT
I found this article very interesting so thanks Chris for taking the trouble to make and post the vid. Although the use of "0" rings is pretty well standard now I don't like 'em , I don't like the "stick slip" that often occurs and I think getting the ideal groove size is not easy. I decided to make "proper" piston rings and although my own attempts are several degrees less skillfull than yours they still required much trial and error. These are for my gauge 1 cylinders , They are for 1/2" bore and are 30 thou thick and 25 thou wide. I haven't tried them under steam yet but operating the piston back and forth with finger over the ports they show a definite powerful suck and blow and work easier and smoother than an "o" ring. The width and thickness allow springing over the piston without breakage and were determined by trial and error. No way could I make a clupet version this small but I have tried 2 rings back to back. Whether they will work under the stress of a working engine is yet to be determined. However I got to thinking about Cord rings which we used to fit years go , they were made from spring steel as far as I can remember so that might be my way to make a clupet ring for my little cylinders. Dan.
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Jun 22, 2023 9:02:22 GMT
If you make any metal piston ring then turn a precision 'sample bore', of identical and precise size, into which you can insert the ring, and then hold it over a light source and observe any 'leakage' of light showing.
A colleague and I have done this and found that new rings are invariably not true to the bore when set to that exact diameter. Leakage will be considerable.
I would suspect that the Clupet rings' success is that it passes this test better, rather than any benefit from the longer leakage route by not having a conventional ring gap.
Norm
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Post by chris vine on Jun 24, 2023 0:16:11 GMT
One vital point for making piston rings, which was explained by Tubal Cain in his series, is that when heat treating a ring which is held open to give it its spring, then it is important to constrain the ring in a little fixture which holds it from the sides (ends), IE Clamped axially.
This holds the ring in the shape it has been opened out to while it is stress relieved. I have seen in print that you just put a spacer in the gap and then heat to red heat. This will relieve the stresses very quickly at the highest stressed point - opposite the gap. Once that has happened, there will be no stress to relieve around the rest of the ring, so it will no longer be round when put back into its bore.
This clupet was a little different in that the outside was machined round and to size while the ring was held axially. A different system.
Thanks for all the good comments! Chris.
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Post by steamer5 on Jun 24, 2023 1:29:20 GMT
Mr Crispan has done a follow up video on his adventures in making standard piston rings, here’s the link if you haven’t seen it. He talks about the need to axially expand the ring correctly to avoid what Chris says above youtube.com/watch?v=2mqdIA3SFJs&feature=share9He was going to make the info he shows available ….. Cheers Kerrin
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SteveW
Elder Statesman
Posts: 1,397
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Post by SteveW on Jun 25, 2023 13:22:33 GMT
I followed the above Youtube link and then found this: Making Big Piston Rings from Scratch ... Fascinating and gets around the bore concentricity problems outlined above. Reminds me back when we stopped for tea after riding down from Munnar in Kerala we watched a local cutting short lengths of cira 1 inch diameter steel plugs from a six foot or so bar. Instead of hack sawing them off he dinked them all round with a big hammer and cold chisel and then broke the bits off by clamping in his vice and swinging on the far end. Another time we saw a great long bar sticking out the doors of a little engineering shop and extending half way across the road. The other end was in the big chuck of a big lathe and the whole lot was spinning round. There was a couple of crude steadies along the bar supported on bricks. Sorry, a bit off topic but its easy to forget how other places just get things done and without the faff.
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SteveW
Elder Statesman
Posts: 1,397
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Post by SteveW on Jun 26, 2023 13:54:22 GMT
Guys,
a bit off topic but ... Watching the video above the simple way of making simple piston rings would be to produce an over sized CI tube to the nominal dimensions, add a gap then very carefully squeeze the thing up in the chuck enough to close the gap then trim to perfect size and part off. No heat treatment.
What could possibly go wrong? I guess loads of things but sliding a bore sized ring over each embryo ring prior to cutting off would at least limit how far the little guy would ping off to.
Discuss ...
(1421)
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,909
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Post by JonL on Jun 26, 2023 19:50:24 GMT
Would that be concentric enough to work?
We all watched Chris' how-to video on youtube in the crew room today. Lots of shaking of heads in bemused disbelief, in a good way!
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Post by chris vine on Jun 26, 2023 22:00:43 GMT
Hi Steve,
It sounds like a cunning plan and I am sure you could make rings like that. However, I don't know if they would be truly round in the bore when squeezed to fit inside.
There is some maths with Tubal Cain showed, that if you make the ring to the correct size, then open it up with a sizing piece to spring it open and then heat treat (with ring held axially to stop all the stress relief happening at the highest stress (opposite gap) first) then when squeezed shut, it will be truly round in the bore. Also, I think it also gives a constant outward pressure all round the ring.
Without doing some maths (which I have forgotten how to do!) I don't think you can assume it will be round and with even wall pressure with your scheme. Might be though!!
Chris.
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Post by chris vine on Jun 26, 2023 22:06:24 GMT
Hi John,
Glad the bemusement was in a good way.
The real bemusement for me is that 127,000 people have now seen it and 20% of those have watched right to the end...
Now I will have to make some more! Chris.
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