I was gettting ready to do a Vibrobot workshop by attaching some salvaged toy motors to battery packs, and I was scratching my head about how to make eccentric weights for the shaft to make them vibrate. Doh! I have a 3D printer! Customize with shaft diameter. A later version may allow other customization as well
You might want to fiddle with the shaft diameter to get a tight fit. I know on my printer (without a fan) PLA tends to close up around the hole if it's too small. You can also insert the shaft while the plastic is still warm and as it shrinks it will grip the shaft.