[Jared]

I would divide it in thirds to more closely replicate the convex shape if you're cutting a straight angle. But if it's easy to disassemble the conveyor and remount the rollers in the lathe you could try .25" on each end first and cut more if it still doesn't work right. If you're going for a curved surface I think it would be best to make the entire surface a constant radius so the point of largest diameter is more concentrated in the middle instead of being two-thirds or three-quarters of the length, if that makes sense.