Quote:
Originally Posted by Rauhul Varma
Is it really that common in FRC to add 2-3 thou? (I honestly don't know) For every gearbox I've designed I've only added half a thou and haven't had any problems with wear.
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Can you really hit a half thou accuracy? Even running finish and float passes and really getting to know the machine, program, and material, I can usually only hit around 1-2 thou accuracy on our CNC for stuff like hole to hole distances.
Yeah, 3 thou is the standard number. I've heard that it mostly came into being in a time when FRC gears were pretty low quality, VP gears nowadays are high enough quality that you don't really need the adder. Another reason for the adder is that if you have a bit of runout on your shafts, or poor quality gear teeth, and you put the gears at the nominal pitch diameter, there'll be places in the rotation where the gears get sort of jammed together, and you lose efficiency. Adding a few thou helps make sure that the gears aren't getting jammed into each other in case of tolerance issues somewhere else.