I really like the design of a top mounted spool that rides on bearings, such as my Prusa-Top Spool Mount thingiverse.com/thing:16046 which was adapted from the MendelMax Spool Mount thingiverse.com/thing:13329 But after finishing my first spool, I faced a dilemna. Either:
1. Continue to buy a new spool for every new filament batch, or
2. Re-wind my empty spools with fresh filament.
Buying a new spool every time not only costs extra, but I felt it would be quite wasteful, and BEING WASTEFUL IS FOR JERKS!
Then I tried to re-wind a spool by hand. That turned into a tangled, frustrating mess very fast. I quickly realized that WINDING SPOOLS IS FOR CHUMPS!
Being neither chump nor jerk, I devised a third option: a spool with a removable face, so that a coil of fresh filament could just be loaded on, and then reassembled. The printed parts along with some nuts and threaded rod help hold the split spool together.
Parametric python scripts included for use with FreeCAD.
Updated with a symmetric 3 "spoke" design to avoid pinching spool on one side. After testing this, the parallel-ness of my spool faces was improved and I decided to remove the old models with only one "spoke".