Originally Posted by
choddo
No they’re rotating in the opposite direction to the spindle, while they move in the same direction
although I think I get the thing about the position of the force applied shifting around the diameter of the cup as the crank moves.
OK, got it, yes, the balls are rotating the reverse of the spindle. But they're along for the ride with the spindle. Worst-case forces is if the balls start to seize up, and in that case, the cup will try to rotate in the same direction as the spindle, which would try to back out the cup, except, the precession forces, based on the rotating radial load and slack in the threads, wants to rotate the cup opposite the spindle direction, tightening it.
There another thread right now, suddenly spindle got tight; Lockring had loosened just enough that the cup promptly tightened on the bearings, due to precession.