Originally Posted by
HillRider
Could you explain this further? How does a shaft turning between two sets of bearings orbit?
The balls are rotating counter to the direction of the spindle. The bottom of each ball where it contacts the spindle moves in the direction of the spindle causing the top of the ball where it contacts the outer race (bb cup or cartridge shell) to turn in the opposite diredtion and, in effect, tend to tighten the cup if the threads are pitched correctly. Of course the friction isn't much but it isn't zero either.
The ends of the shaft experience orbital force against the direction of rotation. It's a physics phenomenon that I remember from the old engineering days, but it's been too long for me to rememebr the terminology or I would just Google it for a clear explanation. I'll keep trying and if I find it I'll ressurect this post.
Agreed, it's not zero; my not-too-clear point was that it shouldn't be enough to loosen a properly tightened cup.