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Unread 15-01-2017, 17:36
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mman1506 mman1506 is offline
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Re: Machining precision required to make custom gearboxes

Quote:
Originally Posted by JesseK View Post
What about oblong holes? Our DIY gantry-style CNC consistently cuts oblong bearing holes that are exactly correct in the 'X' direction, but approximately 0.001-0.002 off in the 'Y' direction. That's about as close as they could get before needing to move on to other things.

As the guy CAD'ing our first-ever custom (non-drivetrain) gearboxes this year, is there anything I can do to make this a non-issue? The concern for us is gearbox longevity in ~120 matches between March & November.
Your probably going to be fine, the 20DP gears commonly used in FIRST are purposely larger than necessary so they can handle being abused in low precision gearboxes and high sudden torque situations. Usually the failures of gears in FIRST are either due to gears being too small and cracking at propagated stress points of the hex shaft or flexing and allowing the gear mesh to become far too loose (the VEX Ball shifter 3rd stage seems to have this issue). In the scheme of things the amount of time FIRST robots run is very short and wearing your gears to the point of failure is very unusual unless something is really wrong like the mesh being too tight. This why its common to add .002" to the C-C mesh of gears in FIRST.
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Last edited by mman1506 : 16-01-2017 at 05:43. Reason: DP correction
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