Atlas Lathe Change Gears from OpenSCAD, 96 teeth and 120 teeth, customizable

What? 3D printed gears for a metal lathe?? Preposterous! Hang on... they actually work. Don't believe me? Check out this video from the esteemed Tubalcain if you need proof: https://youtu.be/V6Aq0d1070I

These gears were inspired by Gadget047 (https://www.thingiverse.com/thing:143893). I printed out those gears and they have worked OK. However, there were no oversized gears (e.g. 120 teeth) to be had, and I found the lack of tolerance on the gears central shaft and keyways to be problema