Hi all. Got a vintage Clinton Diver with screwback case. My problem is that even though I can turn the cover counter clockwise the cover does not finish unscrewing. I have gone as much as 30 turn with not luck. Any Ideas.

Thanks in advance.

Chris, the case could be full of gunk around the threads binding the seal in the case.
Unless the case back is clamped in the remover, you can't lift the back as you turn it, so it 'stays put'.

I keep an old buff stick (with the paper removed) for getting things like these off.
Put a spot of superglue in the middle of the back, drop the stick on it, and when grabbed, pull as you turn and the back should lift off.

The glue shouldn't have set long enough to make a hard set, so should break free, then soak the glue in solvent to clean up the caseback.

If someone's stripped the threads, then that's a different ball game, but the stick and glue job should even lift those off.

John