Lapping machine for piston rings

[Foketry]

I know this post is more about lapping but I wanted to make sure you were aware of this link where it discusses ring making in more detail, the Trimble method & other related input.

In the engine i built previously ( Holt 75) i followed the Trimble method
I made all the tools, but I put the rings in the oven at 800 degrees C (1470 F) but the rings become very soft , sloppy and have lost the spring effect.
Then I remembered that, as studied at school decades ago, cast iron heated to over 720 degrees changes characteristics.
I redid the rings again, but only heated to 450 degrees ,the rings were ok , however, I had about 30% of rings with compression problems .

I am now building the Howell V4 engine
To replace a ring on this engine it is necessary to dismantle it completely, including the multi-piece crankshaft
I therefore want to make good rings at the first shot , i am looking for all the solutions to do a good job, included lapping machine .

 

[Foketry]

The finished Lapping Machine

New motor

 

[Foketry]

the lapped ring, now i have to turn the outer diameter and the inner diameter

the ring before lapping and after lapping

 

[petertha]

Very cool. How did you take that magnified picture?

 

[kuhncw]

That is a very interesting machine and it gives a nice finish. Well done.

Chuck

 

[Foketry]

Very cool. How did you take that magnified picture?

is a USB microscope , 12 $

https://s.click.aliexpress.com/e/bMj7Z4jA

 

[stevehuckss396]

I put the rings in the oven at 800 degrees C (1470 F) but the rings become very soft , sloppy and have lost the spring effect.
I redid the rings again, but only heated to 450 degrees ,the rings were ok , however, I had about 30% of rings with compression problems .

Too hot and too cold. You also didn't say how long you left them in the oven. 1100F for 3 hours is what you want. I have made 4 or 5 batches this way and have made good rings every time.

 

[nj111]

Thank you for sharing, it's a great machine! Nick

 

[Mr.McKinney]

That's a great machine for the task. I've needed to lap smaller rings for a work project. I built a small fixture for the task. But I know from first-hand experience that applying even pressure to all sides while doing this by hand, is tricky. It's very easy to end up with rings that are thinner on one side. Thanks for sharing this idea!

 

[CrashedAgain]

I wrote an article on making piston rings in Home Shop Machinist magazine Vol. 37 No. 1 Jan-Feb 2018 (available as a reprint from http://www.homeshopmachinist.net/). Basically I manually lap the sides similar to what Foktry was doing before making the lapping machine but I also lap the outside diameter after heat treating. Trimble's method (which actually dates back to Prof. D.H.Chaddock in Model Engineer magazine 1967) was to machine a couple of thou off the diameter to true it up after heat treating but I always found that difficult. Lapping is much easier.
If the rings lose their spring after heat treating it is a problem with the material. Some cast iron is too ductile and just won't work.
(Which brings up another point......I cannot see any reason why steel rings in a cast iron cylinder would not work???)

 

[Wizard69]

You got some nice results but I have to ask, is that machine built out of glass?