Scuka1 t1_jeayezn wrote
Why do you think it's difficult to make them all nearly identical?
In an automated production line, it's easier to make 100 pieces that are almost identical than 100 pieces that are all visibly different.
Everything is made by machines.
A machine is doing the same motions and using the same tools each time, so the end result is pretty much the same every time.
buildyourown t1_jeb9aft wrote
Tools wear. Every part is going to be a little different. Materials also aren't perfect. Even with lots of quality control 1 heat treat lot might be a little different than another. The grain structure of materials are going to vary slightly. Etc, etc.
Ratnix t1_jebqjzg wrote
We do metal machining for the auto parts we make. The parts we make get randomly checked a couple of times per shift for all of the necessary specifications down to a couple hundredths of a millimeter variance.
If a part checks out of spec, the production of those parts are shut down and an engineer comes out to do what is necessary to make good parts again.
While they are doing that, quality control goes to the parts that were made by the out of spec machine and checks them, from oldest produced since the last line check, to the newest produced, until they find where the bad parts started getting made. They are then quarantined and sorted and measured, throwing out all out of spec parts.
They are all virtually identically, only having slight differences of no more than 0.02mm
Scuka1 t1_jedip7z wrote
Which is why I said "nearly identical", not "identical".
Tools wear, but to the naked eye that's not visible. There's also quality control and preventitive maintenance systems in place to make sure that tools don't wear out to the point where they start producing non-functional parts.
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