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Machining precision required to make custom gearboxes
My team is currently making a (simple) custom gearbox in place of the COTS gearboxes we were planning to use that ran out of stock.
My question is: Do you really need thou precision to make decent gearboxes? Because after looking at some other threads, it seems like even measurements as small as .003" can make a significant difference in the performance of a gearbox. |
Re: Machining precision required to make custom gearboxes
I would say you should be able to relatively easily hold .002" on position of hole centers on a decent quality manual mill with a somewhat experienced operator. That would be good enough for a custom gearbox.
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Re: Machining precision required to make custom gearboxes
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. |
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I second that you need .002" precision at the minimum. Personally I prefer .001". If you do not have a mill, please don't attempt this mid-season- there is almost a saturation of gearboxes available from WCP, Vex, and Andymark. |
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Re: Machining precision required to make custom gearboxes
If you don't have a CNC or a manual mill, you can do this manually. With the typical FRC gears and a simple gear box. you can lay out and drill holes using a machinist scale, scribe, prick punch, a drill press, and a little OCCD. Clamp & drill the side plates together. This takes a lot of care, but is very doable.
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Much more valuable to expend that effort on other areas of the robot. |
Re: Machining precision required to make custom gearboxes
Are there any other teams in your area that have access to a CNC mill or water-jet? Most teams are happy to support other nearby teams with machining or needed parts. FIRST is really a community, we only compete on the field.
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I would venture to think that there is backlash in the router that can be corrected with software (LinuxCNC/Mach/etc.), but I haven't seen their setup. |
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In any event, since the gears arrive tomorrow we'll likely just make the gearbox and report back in November. If we see signs of premature wear during our planned 50-climb test, we'll probably get steel gears and just brute force it. It's in an easy-to-replace spot and we're building a spare as it is. |
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In terms of drill presses. We are fortunate to have a heavy 1/2 press with good bearings. But I get as accurate results by using a 1/4 in Ryobi and either a short 1/8" bit or center bit. |
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