Let's put it another way.
Suppose you've got a gearbox, with a shaft in it, and a stack of parts on the shaft. The shaft with its parts must fit in the gearbox. The gearbox has a max and min size, and each part has a max and min size. The engineer divides up the tolerances so that if they are all at max size, and the gearbox housing is at min size, the parts will fit.
Now, if a gear comes back from the manufacturer larger than its max size, but enough of the other parts are not near their max size, the stack will still fit and it's ok. (But engineering still has to approve the fit.)
This is not in any way a crisis. It simply costs extra money because the out-of-spec part gets bounced to engineering for review.
Yes, I did these exact calculations on the 757 stab trim gearbox.
Suppose you've got a gearbox, with a shaft in it, and a stack of parts on the shaft. The shaft with its parts must fit in the gearbox. The gearbox has a max and min size, and each part has a max and min size. The engineer divides up the tolerances so that if they are all at max size, and the gearbox housing is at min size, the parts will fit.
Now, if a gear comes back from the manufacturer larger than its max size, but enough of the other parts are not near their max size, the stack will still fit and it's ok. (But engineering still has to approve the fit.)
This is not in any way a crisis. It simply costs extra money because the out-of-spec part gets bounced to engineering for review.
Yes, I did these exact calculations on the 757 stab trim gearbox.