BCN3D Sigma Bowden Creep Fixer

Some BCN3D sigmas suffer from bowden tube creep - there are already a lot of shims that fix this happening due to retraction, but on my sigma it happened additionally because of rotation of the bowden tube in its fitting.

This simple mod fixes both issues. Simply print both files, heat up the extruder, remove the bowden tube, loosen the extruder screws, slide in the bowden holder, put the bowden tube in, retighten the extruder screws, add a cable tie _as tightly as you can_, and slide in the