Designed for the 3D Printing Design Contest - Filament Spool Holder!
The idea is to print 2 of these, hang them from the front of the shelves, and then use a piece of 3/4" PVC tubing with them to hang the filament for printing. A wooden dowel rod would likely due in place of the PVC tubing depending on what you have available.
Using PVC for the rods is a relatively cheap way to ensure that the spools move smoothly, but not easily enough to where they get momentum and continue turning when they should not.
Features include our new favorite structural shape, the triangle! The length of PVC or dowel between the supports can be used to customize the number of spools it will hold (within the structural limit of the brackets.