Originally Posted by
Leinster
My question was more at the factory level, rather than the brand level. If the plant manager at a bicycle factory in Taiwan, has their biggest customer, a major American brand, tell them “We want all our Al frames to have press-fit BB, and every single one to this tolerance which will prevent creak, and here’s your budget for that,” what can they do to meet the challenge, short of measure every single point of every frame that comes off the line, and ruthlessly toss every one that’s a micron out of spec?
Statistical process control. This is how bearings are made to such incredibly tight tolerances. Yes you measure them as they come off the line, but you don't just scrap the bad parts -- that's the road to ruin, and eventually under financial or schedule pressure, the tolerances will be waived and the bad parts will ship to the customer.
The idea behind statistical process control is that you watch for variations that are smaller than the tolerance limits, and feed the results back into the process through tiny corrections. You also improve processes to make them more consistent from piece to piece, so the quality measurements are meaningful. This kind of control is done all the time in the manufacture of things like motors, transmissions, and so forth.