UPDATE: This new version makes several improvements.

• The tracks are longer, but the model is still the same size overall.

• Significant changes were made to the internal geometry to eliminate internal bridges that sometimes caused an obstruction with some older printers.

• The thumb hold has been moved and the shape changed to be more comfortable.

This is a hand-held, portable marble run. Turn the outside wheel to lift the bearings to the top of the tracks.  They’ll pop out and run to bottom where they re-enter the outside wheel to start the next cycle.

It is tactilely and audibly satisfying. As the balls enter and exit the tracks, they make a “click-click” you can hear and feel.

It prints easily as one piece. The only assembly is to press 5mm ball bearings into the tracks.

I’ve included two versions of the model – one with loose clearances on the moving parts that should work with most printers, and one with tight clearances that will only work if your printer is really dialed in.

It takes about 2 hours on modern Core-XY printers.  4.5 hours on modern bed slingers. 6-8 hours on very old printers.

You can print it using one color, or set your slicer to do filament changes at various layers to get cool effects. 

Once you print it out, you can press the bearings into the two tracks.  I recommend using about 8 per track.

Any 5mm bearing should work.  Here are the ones I used: https://www.amazon.com/dp/B0FDVZXY6Z (Not an affiliate link).

Just set the bearing on the track, then press it in with your thumb.

Then hold it upright by the thumb grip, turn the outer wheel and enjoy!

I’d love to hear feedback and ideas for improvements.