Originally Posted by
davidad
You are kidding about the same batch superstition, right?
oger (who?) writes:
> Did you know you should only ever use ball bearings from the same
> batch in one side of a race? They're not exactly the same size
> between batches. Never simply replace that naughty one that bounced
> into the corner of the garage - replace the other 10 (or whatever)
> too!
You are making this up. The tolerance between bearing balls is so
small as to be below a small fraction of the elastic compliance of the
steel bearing. Besides, the races of bicycle bearings are so rough
that a tight bearing feels lumpy. In high precision bearings used on
computer disk storage devices, preload causes a smooth viscous drag.
Even for these bearings the balls are not identical but are made to a
prescribed tolerance. I don't believe I understand what you mean by
the same batch. Each bearing is not made in the same finishing
process as the others in a shipment of balls.
Jobst Brandt <jbrandt@hpl.hp.com>
What I'm saying is if you have to replace 18 bearings in your rear hub, and you have a year old bag with five bearings left, don't combine them with a bag you just bought. The old bearings might be 0.12504 inch plus or minus .00001 inch, and the new batch is 0.12506 inch but still plus or minus .00001 inch. So you could end up matching a 0.12503 ball from the old batch with a 0.12507 bearings from the new batch, which could be a significant variation. I'm pulling numbers out of my head trying to illustrate the point, but I've read something to this effect.