RAY POPE shared on Thingiverse:

Rock tumbler

This is a rock tumbler I made to bring out the qualities of brass and
copper printed filaments.
It probably spins too fast here so you can either drop the supply voltage to the motor to 9 Volts (which I did and works well) or increase the amount of cutting material (I used zinc plated small screws) inside the
tin with the object to be shined. It takes a few hours spinning to get results but generally works well. The only thing I would add would be a chain guard to keep the chain jumping off the sprockets which I
will design and upload at a later date. As for now this does the job
for me and beats paying $100+ for a commercial tumbler.

Every Thursday is #3dthursday here at Adafruit! The DIY 3D printing community has passion and dedication for making solid objects from digital models. Recently, we have noticed electronics projects integrated with 3D printed enclosures, brackets, and sculptures, so each Thursday we celebrate and highlight these bold pioneers!

Have you considered building a 3D project around an Arduino or other microcontroller? How about printing a bracket to mount your Raspberry Pi to the back of your HD monitor? And don’t forget the countless LED projects that are possible when you are modeling your projects in 3D!