The rubber band powered penny launcher is a staple of engineering inter office warfare. Although it could just be the graduate student research group setting. In any case I saw a few similar disc launcher things but nothing that really suited my needs. This is just a simple version I quickly tossed together. The range is easily across the lab using standard rubber bands double wrapped on each side.

For those not in the US, the penny is about 19mm across and 1.55mm thick.

Update 3/1/12 I’ve added a version with fixed geometry. It slices without any errors and warnings for me. If you somehow get an error please let me know.

Print all 3 pieces and assemble with #4-40 screws. About .5 inch in length is needed. The front screws need to be tight and the back screws need to be loose so it doesn't jam.

You'll need to make the slider (piece 3) solid so it doesn’t break easily. Even then they will break occasionally in normal operation. It's a quick piece to print and replace anyway.