Summary

Didn't fancy the holders mounted above the printer due to the angle the filament enters the extruder. I've heard of extruder levers being worn through by filament entering at an angle.
So I came up with this design which holds the spool more in line with the entrance to the extruder.
It takes spools up to 85mm wide.
You may need to rotate it by 45° in your slicer to get it to fit on the bed.