# making piston ring for Corliss Steam Engine



## ZAPJACK (May 24, 2020)

Dear all,
I need some help to make piston ring for a Corliss steam machine.
Why is there an offset between external & internal diameter?
How is possible machining the "Z" opening of the ring?
Thanks for help
LeZap


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## Cogsy (May 25, 2020)

It looks to me like the designer wanted to completely eliminate any ring gap so the ring is made oversized then split. Then the side of the ring on one side of the split is milled down to half thickness, the ring is flipped over and the side on the other side of the split is milled down to half thickness. This will make the 'z' which when they go together eliminates any ring gap and allows the ring to close up enough to fit the bore.

The problem I see is that the ring will no longer be round on the O.D. and will likely leak far more than it would have using a 'normal' ring gap. I'm only guessing, but the offset ID and OD could be the result of turning the outside after splitting, making the 'z' and compressing it. This would result in the OD being round and should make a better ring than using the instructions.

I've never had anything to do with steam but for IC engines you need ring gap for thermal expansion. I'd think that this would be the case for steam as well but I'm not certain. If you have zero ring gap and the ring needs to expand more than the bore then you are certainly going to increase friction. Maybe with the materials involved this isn't a concern in steam.


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## ixb1 (May 26, 2020)

Machining these "Z" rings looks a bit tricky. It would be a simpler make two thiner ordinary rings and gaps oriented opposite.


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## Richard Hed (May 27, 2020)

ZAPJACK said:


> Dear all,
> I need some help to make piston ring for a Corliss steam machine.
> Why is there an offset between external & internal diameter?
> How is possible machining the "Z" opening of the ring?
> ...


These rings are made of cast iron?  You are using CI?  I made this quite differently, I made the piston one solid piece of aluminum and simply bought rings for lawn mower that were the right size.  When cast iron gets down to very thin like that it is going to be very brittle and likely to break several times before you get a good one.  Good luck on that.


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## ZAPJACK (Jun 10, 2020)

Thanks you for your help, I now better understand the necessity of offset ID/ED
The two piston rings are ready. I made it in cast iron GGG60 quality
LeZap


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## leerkracht (Jun 10, 2020)

The rings are old style 1/8   3.175mm is to  much  , smaller rings perform better  and wear less (ring and cilinder )  1mm is better  , modern (race) engines all uses small rings   you can cut ist at an angle if you wisch


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## Richard Hed (Jun 10, 2020)

leerkracht said:


> The rings are old style 1/8   3.175mm is to  much  , smaller rings perform better  and wear less (ring and cilinder )  1mm is better  , modern (race) engines all uses small rings   you can cut ist at an angle if you wisch


You are a Magician!  How many tries did you have to make?


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## SmithDoor (Jun 10, 2020)

Making the blank on the lathe make tub. Use cut off tool to make each ring blank.
This type of ring take jig to do milling for zee. You need flip the ring over to do both sides of zee.

Dave



ZAPJACK said:


> Dear all,
> I need some help to make piston ring for a Corliss steam machine.
> Why is there an offset between external & internal diameter?
> How is possible machining the "Z" opening of the ring?
> ...


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## werowance (Jun 10, 2020)

but how did you prevent the ring from "egging" or "ovaling" after compressing it past its original base circle so the z overlaps?  or is the ring "springy" enough that when inserted into the cylinder it will take on the circle shape of the cyinder?


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## SmithDoor (Jun 10, 2020)

I did worry about egging 
After runs for short time the egging will go away.
You can make a jig and grind out the egging.
If ever work sometime that have not made parts for long time it is only thing you do

Dave


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## peter2uat (Jun 11, 2020)

May  I jump in with a (lengthy) article on this theme I have found somewhere on the 'net which explains in detail the 'how to' & the 'why' to the making of piston rings, by Prof.Chaddock and Tom Walshaw (the REAL Tubal Cain, from 'the English magazine 'Model Engineer') in the '60s. This to my knowledge is THE method to making those rings for model engines and has not been surpassed by any other way.


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## leerkracht (Jun 11, 2020)

I used the method from George Trimble  for over years now  with 96% perfect rings , good sealing from the first stroke  , i lap the bore of my cilinders (from nodulair cast iron GGG40)(meehanite) instead of honing them  
a new made engine  runs from the first of the second flip by hand ( propeller )


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## SmithDoor (Jun 11, 2020)

Good paper on pistons rings.
I have not lap piston rings it would be on more jig to build. 
I just made the ring and let engine run for lapping.

The biggest problem I had was find good cast iron to make the rings. 
My main source of cast iron today is weight lifer weights.

The best cast iron I used and purchase is class 45 made in the USA foundry. But the is very costly no bad spot just clean cutting wears great, I used for wheels on doors.

Thank you for your paper
Dave



peter2uat said:


> May  I jump in with a (lengthy) article on this theme I have found somewhere on the 'net which explains in detail the 'how to' & the 'why' to the making of piston rings, by Prof.Chaddock and Tom Walshaw (the REAL Tubal Cain, from 'the English magazine 'Model Engineer') in the '60s. This to my knowledge is THE method to making those rings for model engines and has not been surpassed by any other way.


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## peter2uat (Jun 12, 2020)

leerkracht said:


> I used the method from George Trimble  for over years now  with 96% perfect rings , good sealing from the first stroke  , i lap the bore of my cilinders (from nodulair cast iron GGG40)(meehanite) instead of honing them
> a new made engine  runs from the first of the second flip by hand ( propeller )


Thanks for your mentioning Geoge Trimble - I had his name on the tip of my tongue...
There is a nice description of his method in 'modelenginenews' -->


			How To Make Piston Rings
		

explaining the differences beween his style and the Chaddock-Walshaw way.
I'd say - stirred or shaken? both methods function in producing perfect fitting piston rings which need very little running in - if at all.


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## MachineTom (Jun 12, 2020)

I made my Corliss rings as the drawing showed. First turn the outer diameter, place piece of brass, in one of the chuck jaws, half the thickness of the offset, so a .015 will yield 
030 offset in the ID.
Then measure for half the width. And make the cut, flip an do the other side of the Z.

I used the supplied CI. For the rings, but made the piston from brass, rather than the CI called out in the plans.
Tom


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## ZAPJACK (Jun 12, 2020)

I do it simply with a four independent jaws chuck.
At first the external diameter à the right dimension,
than fit the offset (0,4mm) and check with a Pupitast
Turn the inside diameter at final dimension.
Cut and do the Z
LeZap


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## wazrus (Jun 12, 2020)

A friend whose business was reconditioning hydraulic cylinders, ran a very critical eye over one of my (hopefully) cylindrical creations. He pronounced it parallel which, he said, was much more important than the finish of the bore. I had agonised over that finish, considering many types of honing apparatus, but he felt that any sort of honing operation - particularly of the type I was considering - (the 'economy model) would almost certainly bell-mouth my nice bore and anyway, the cat-iron rings would do the job quite effectively. It follows that I've always tried for as good a finish as possible 'off the tool' and have always made my own cast-iron rings, as per a few older Model Engineer articles.


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## a41capt (Jun 13, 2020)

I tried my hand at making my own piston rings recently and found it to be relatively easy, even for a rank hobbyist like myself. That being said, that “Z” ring cut looks amazing, and I wish I was capable of pulling that off.  How ever in the world did you get them springy enough to seat outward?  I use the old mandrel and heat ‘em til they drop method.


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