The ring blank is mounted between tailstock and chuck (just a friction drive) and a spigot is cut
This spigot is used to hold the piece and the other face is trued up and the external diameter is turned
A second spigot is cut in the other side
The recess is enlarged until the ring thickness is right
The ring is cut about half way through and some sanding and finishing is done
When the ring is finally detached it needs to be protected. A catcher disc is screwed to the centre