To make a free moving ring held inside another ring, I'd use my
Fabricate the ring that moves. Then make a wider, but smaller ring.
Then very carefully flare the edges of the wider ring to hold the
Another way would be to cast three rings - the center one, the
inside one with one retaining wall, and a separate retaining wall.
Solder the separate retaining wall to the inside piece, after
applying an antiflux to the moving ring.