Ali wrote:

Just me again?

Sorry, I am on a field trip.  ;)

With regards to your question, you should aim for a tolerance-field k5, i.e.

+18 to +3 1/1000mm undersize, in order to prevent deformation, I'd aim for 0.01mm over on the outside and 0.01mm undersize on the inside. Nothing that's too hard to do with decent lathe tooling and a bit of patience. The thing that I would personally spend a lot of (extra) thought on, would be, whether making a steel ring in only very light interference fit, e.g. 0.003 to 0.005, but with a strong fit on the inside, e.g. 0.01 to 0.015 as the bearing would expand the steel ring quite well and you could use some loctite bearing glue to permanently fit the shells to the cases without having to fear them coming loose. Additionally this would mean a very low risk of distortion of the ring, when coming to think of it.

That being said, I haven't designed anything like this ever since I left technical college more than ten years ago...

Cheers,
Greg