Drive Train Gearboxes

[magnets]

Originally Posted by thinker&planner

Thanks for all your responses.
When we talked to machinists that make 45T hybrid magnets, they said that we would need precision down to at least .0005". Is this truly necessary for FRC gearboxes? I think that they are used to metric gears with much smaller diametral pitches where that kind of precision really maters.

We were told repeatedly that you can't waterjet gearboxes, because you just can't get the precision that you need for press fit bearings.

Basically, all our machinists said that they would not make a gearbox for us unless they would be mass-producing them. I understand that calibration and setup takes a long time, but if there's no fancy lightening pattern, couldn't you just put two plates together and make all the holes relative to each other? Later, you could cut it out to the right dimensions (roughly), as long as all the holes were correctly spaced.
Thoughts? Thanks!

If you're talking about cutting plates, then your machinist is very wrong. You can easily get by with 0.003" (6 times what he said). The issue he may be worrying about is if the gears get too close to each other. They rub, have a lot of friction, and heat up. It's one of the reasons teams add the magic 0.003" between center to center distances, so that if it's off, it still works. The extra slop also makes the gearbox run better for applications with little wear in time and low usage. remember, the thing only has to work for less than 100 hours, which is why companies like vex pro can get away with selling aluminum gears, which are more than good enough for FRC, but not for a transmission in your car, or something like that.

The only thing you really would need crazy tolerances for are press fit bearings, but you can ream them yourself.

You're right in saying that the plate is nothing more than a few lined up holes. The rest of the plate (mounting holes, lightening holes) don't really need to be anything special. I'm not a machining expert, but I've been able to make made our practice robot's gearbox plates in under 15 minutes each.