Print-in-place planetary gear fidget toy

6.19.23 EDIT: Added a few more versions with different hole configurations. Pick whatever you like the best :)

Onshape link

This seemingly simple toy isn't just fun to play with, it's also a perfect way to demonstrate the capabilities of 3D printing. The meshed herringbone gears would be impossible to assemble if manufactured separately, they must all be made together in place.

Keep this away from small children; they could break the outside gear and choke on the inner ones, or pinch their fingers in the gaps.

Printing instructions

This is not an “easy” print, so be warned!

Print with standard settings; I used .28mm layer heights and 15% gyroid infill as I usually do. The first layer has a very small cross-section, so make sure your bed is leveled and consider using something like Magigoo or glue stick to aid in adhesion if necessary. Use a material that doesn't warp heavily; PLA is what I used but PETG should work nicely too if you prefer it.

Pinching the inside while twisting the outside should free the gears, although they will likely need a bit of breaking in and lubrication to become nice and smooth.