This is the Umake Gearbox Keychain, the only difference being I enlarged the hole in the gears .2mm to make assembly easier and the gears spin freely without sanding. When trying the original gears, I broke the tabs for one gear, and the other was so tight it wouldn't spin at all.
I thought too many people were complaining about the tabs breaking when inserting the gears for it to be a coincidence or "bad quality filament". In a later comment, it was noted the designers were not using PLA, but PLA/PHA blend for best results.
In studying the model I saw there was only a .2mm tolerance between the tabs and the gears, so I opened it up to .4mm (the same as my extruder nozzle). The result? Gears snapped right in place without any damage and spin fairly easy without any sanding.
Printed with PLA "bad quality filament." The sample shown was done with .1mm layer, 2 shells and 40% infill on a CTC Dual.
I hope this helps others enjoy this great design by Umake!
Note: The keychain has not been modified, I only included it so all the parts would be in one download.
Just print and press gears into place. I did wipe a single drop of oil on the tabs "just in case", but I dont think it is needed since the tolerance are looser than the original design.