Updated: Uploaded a 2.0 version that is smoother, better reinforced, and still prints without supports in a single piece.
This is an entry for the 3D Printer Nerd Design Contest for creating a spool holder to mount to the front of his Filament shelves. This design is intended to be simple to print and use, though it is a big long (probably have to print on the GMax). I decided to style it somewhat after the shelf brackets themselves.
The idea is to slide the long end in under the gap between the spools and the front wood crossbeam. This will curve in and slip under the back wood crossbeam. When placed correctly, it should brace against the bottom of the back crossbeam, while gripping the top crossbeam between the slight lip and the front bracing.
The feeding filament spool will be placed on the bar sticking out in a perpendicular alignment to the spools on the shelf. The bar has a curved inner surface to attempt to wrangle the spool into a centered position while feeding, regardless of the spool size.