Pepper,
as long as the balls spin slower than the disc under them then its good, if they act as bearings and just roll with exact speed of the the plate/disc then they wont polish, the Diamond is a open top with a sprocket in the middle and it is just the weight of the balls and the outward fore from spoinning that polishes them, on the laft side where you put the polishing compound if you put alot some balls spin faster than others in the beginning because the friction is higher, at the end of a 20 minute cycle they are just free rolling, Joe is on the right track, you dont want the balls to not move because the surface you would polish would be small, if they move less than the turn table then your golden because you end up polishing the whole ball at once, thus ending up with evenly polished balls.