The iron plate, on which the two fixtures are sitting, was made from a 6" round of cast iron. I turned it on the lathe to clean up the edge, then stuck it on the shaper to flatten the top. Finally I hand scraped to get it as flat as I could. It's as flat as can be measured in my shop, and gives good results.

The left hand fixture is a piece of scrap steel bored out to take a piston ring, compressed. You can see the shoulder in the bore: that's where the ring rests. The top edge of the ring then sits proud of the fixture. It's a convenient way to hold onto things while lapping.

On the right is the mandrel used in heat treating the rings. After being bored to thickness and cut to width from bar stock, the rings are split with wire cutters. I used a fine file to clean up the breaks, then slipped the rings onto this fixture. The small rod going up the side is the right thickness to hold the gaps correctly apart. I wrapped the whole in stainless steel foil and heat treated it to anneal the rings. When they came off, they naturally sprung open to the right gap so that they would apply the right amount of pressure to the cylinder walls.

This turned out to be a good method of making the rings. You can find fuller instructions (there's some math involved) in back issues of Strictly I. C. Magazine.