What is more fun than a spool holder and more useful than a marble machine? A spool holder/marble machine! This extruder-driven marble machine uses 6mm airsoft pellets as recirculating bearing balls for a friction-free spool holder. When you get tired of watching your printer print, you can now keep yourself entertained by watching your filament spool turn! Designed for 8" diameter (nominal) spools, 3 1/4" wide or less.
New: I've just added a "slim" version that is more stylish and use a little less filament.
Watch it go: https://youtu.be/DcY06NCV014
Print one left-side, one right-side and two screws. The screws print on end, so add a brim to keep them from coming loose while you print. The "slim" version of the right and left sides are functionally identical to the original versions, but they use a little less filament and print a little more quickly.
Press the left and right sides together over the two screws and then start each screw into both sides simultaneously. Adjust the width to match your spool. Put 33 airsoft pellets (6mm dia.) in each track than then place your spool on top so that when you pull the filament, the balls roll up to the top end of the ramp.