Spannerhands rewinder spool

thingiverse

This is an auto-rewinding spool designed for use with the versatile Spannerhands spool system, a remix of which I have published online at Thingiverse. It enables direct connection of the PTFE tube from a Spannerhands box to an MK3S/MMU2S printer's PTFE tube without the need for a filament buffer. This project is a remix of Vincent Groenhuis' Integrated Auto-Rewind Spool Holder, where I have utilized his parameterized SCAD file to create a spool holder with a diameter of 88 mm and no rims, adding an axle and mounts specifically designed for the Spannerhands box. The mounts are intended to be printed in flexible materials with varying diameters. The length of the mounts and axle is carefully chosen to ensure they lock securely into place within the box. Additionally, two or four flexible rubber rings can be slid over the roll to increase friction against the spool. However, after some experience, I have concluded that using these rubber rings tends to create a retraction force strong enough to cause problems when the MMU hands over filament to the extruder, so I no longer use them. The principle of operation is based on serially cascaded springs inside the roll, which are fixed at one end by the axis and then attached to the box via flexible mounts. At the other end, the springs are secured to the roll using cogs. The roll connects to the spool through friction. When filament is extruded, the spool turns the roll, increasing tension in the springs until the spool begins to slip against the roll. From this point, tension in the springs remains relatively constant. If the friction force at the slipping point is sufficient, the tension in the springs will be enough to rewind the filament once it is ejected from the printer.