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.
