Thanks, Jur, but I owe the idea to rhm (Rudi). Amazing what you can do with a bench grinder- after the sledgehammer, it's my favorite tool

And, alecw, I was thinking about whether the cups would loosen up on you, and I believe the cups will tend to *tighten* from precession. So if the BB you have in there doesn't shift around now, I bet it will stay snug over time.