VEX pro bearings tolerances

[Chris is me]

Just to further reinforce the points everyone else is making, for our CNC, our tolerances, etc. we found that we needed a 1.127 hole for an easy, if slightly loose, press fit. Your mileage will vary. If you're using a CNC to make these holes I would suggest making a template of holes in 1/4" plate from 1.124-1.128 and seeing how bearings fit differently in each hole.

[Joe G.]

One thing to be aware of with laser cut bearing bores. Typically, the laser will leave a small burr on the edge of the hole at the entry/exit point. If left untouched, this burr will prevent the bearing from pressing in, or compress the outer race enough to inhibit the bearing's motion.

We send our sheet metal sponsor parts with bearing holes drawn as the nominal bearing diameter, and they press just right, maybe just a little loose, when this burr is removed. We always use rivets and washers as bearing retainers for some extra insurance, but in properly designed mechanisms, I think they'd be fine without them.

[Mk.32]

Ah the fun games of tolerances...

Basically all the bearings you get will come dead nuts, IE 1.125 bearing will be 1.125 +/- .0005 at worse probably better. To do a proper pressfit, (ie you need a arbor press to install/remove the bearing) for the FRC sized bearings generally it's +.001 to .0015. Press-fits are precision operations.

In my experience laser/waterjet generally at best hold maybe +/- .005 consistently. So trying to achieve a pressfit, your luck may vary. It really depends on operator skill and then fine tuning of dimensions to the machine. Also you have to worry about burrs and tapers, which this type of cutting is infamous for.

Since I don't have constant access to a waterjet/metal cutting laser I generally CNC my gearbox plates and etc. To do it right you have to do test cut some pieces generally, and test your tool for wear and add some tool compensation. And worry about surface finish, deflection etc. Not that it's hard, but it takes a bit of practice.

If you are set on laser/waterjetting these, figure out what kind of quality you can get from them. If it is to poor just allow for a slipfit and design in some mechanical retention of the bearings.