[Bennett548]

548 has quite a bit of waterjet experience, so I'll let you know how we do gearboxes. This only applies to our waterjet and waterjet software, so make sure you try a test piece before cutting too many parts.

We waterjet to 1.125" exactly. This makes the hole larger than 1.125" on the top, and smaller than 1.125" on the bottom. There is usually a burr where the waterjet starts and stops, so first we file that away with a half round file. Then we use a half round file going around the small side of the hole to evenly remove the far side of the taper, hopefully keeping the hole pretty round. You just keep test fitting the bearing to try to get a snug fit. If you go too far use some CA glue to hold the bearing in.

I know this isn't the correct way to do it, but it works well enough for us and hasn't really caused problems, so we will probably keep doing it that way. We have used an adjustable reamer too, but I don't think it made much of a difference.

Having a perfect hole for the bearing really helps it run longer and smoother, but FRC robots don't run long enough for it to matter.

We add 0.002" between small gears (like a motor pinion), and 0.003" between larger gears on an open gearbox. 0.002" for all gears on a closed gearbox. The extra distance in the open gearboxes helps when they get filled with dust and carpet fibers.

Edit: This is for 0.25" aluminum gearbox plates. As s_forbes's post reminded me, thinner stock means more of the hole is the correct size, reducing the need for filing. At 0.500" thickness we waterjet undersize and drill out the hole.

For all holes that will be tapped, waterjet undersize and drill before tapping. For example, for a #10-32 in a 0.25" aluminum plate, we waterjet 0.120" dia pilots.