My submission to the 3D Printing Nerd Shelf Spool Holder design competition.
When designing this spool holder, I aimed to optimise strength and simplicity within the design constraints of the contest. I was particularly concerned that If I attached the spool holder to only the front timber, while it would easily carry the vertical load, the twisting moment from the spool holder could cause damage to the shelf brackets; particularly if many were attached to the same timber.
For this reason I opted for this levered design, where the bending moment from the spool would be held with vertical forces on the front and back timbers. I used large fillets and undercuts to reduce stress concentrations at the corners, and changed the thickness based on the bending moment along the beam.
This design is very secure when holding a spool, but can easily be removed by unhooking it from the front. It can be positioned at any point on the shelves without interfering or needing to move any of the stowed filament spools.
This prints all in one piece, without any support material, on its side for maximum strength from print orientation. This does mean it is quite long however (about 320mm) and doesn't fit on my standard 200mmx200mm print bed; the printed example is at 80% scale. I've also included the Fusion 360 file if you need to make any minor adjustments ;).
Update: I've adjusted the text on the model to make it larger and generally much easier to print.