filament spool holder
The scissor mechanism makes it easy to adjust the width of the spool holder while also holding it firmly enough to keep the set width. I also takes very little space when folded.
Print-in-place roller bearings
While four skate bearings is not much money I still think that it's much more fun to design something that can be completely 3d printed, if that can be done without compromising with the function of the thing.
These roller bearing wheels fits this use case very well. The cage keeps the rollers rolling straight so they don't jam, and also keeps them from grinding against each other. The cage is also optimized for 3d printing, there are no difficult overhangs and all bridges are straight, so it should be an easy print as long as the printer is correctly tuned.
The friction between the spool rim and the wheels is quite low so the bearings must spin really easy to keep the spool from sliding against the wheels. This design actually works, all four wheels do rotate with no slipping between the spool and the wheels.
They should come off the plate more or less ready to spin as the tolerances are intentionally quite loose. If they need much work to break loose, the tolerances can be increased in the 'settings' spreadsheet in the FreeCAD model. The wheels are based on this design: https://www.thingiverse.com/thing:3240362
No glue or screws required. Connect all joints of the scissor before pressing the sliders into the base halves. The orientation of the slots in the joints prevent them from coming apart once the slider is mounted in place, so it must be assembled in the correct order.
FreeCAD source code included
because it's way more fun when you are free to improve the thing. The render is done with blender, blend file also included.
No support needed. It's a good idea to split the bearing wheel in your slicer before slicing so each roller is sliced independently. Using e.g. triangles infill pattern in Slic3r makes a nice symmetric infill in the rollers this way.
It's also a good idea to print one of the 'threaded_pulley' wheels first, if it doesn't work for you then there's no point in printing the rest of the parts. I have added a 'threaded_pulley_loose' that have a lot bigger clearances between the bearing parts that you can use if you are unable to break free the tighter one. The roller bearings might be smoother if you set 'seam position' to 'random' or something similar to avoid having all layers start and stop in the same spot.
Fixed a small error in the scissor arm joints