This is a much more refined version of my winder for spooling home made filament. The filament drops from the extruder (ideally mounted vertically) and loops back up to the winder. At the bottom of the loop is a row of photocells with a laser shining on them. The photocells track the location of the filament's shadow and modify the speed of the spool to keep it in the same place, usually +/- about 2mm.
The filament passes through a 360 degree loop of PTFE tubing which adds just enough friction that the filament will be pulled tight as it winds on to the spool. When it comes out of the PTFE tube the filament passes through a guide operated by a servo, which spreads it across the width of the spool.
There is a switch to change between auto mode, (speed controlled by the sensors), and manual mode (speed controlled by the knob). When holding down the left button, the knob will move the guide to position it at its left limit, and the right button will do the same for the right limit.
While in manual mode the middle button puts the sensors in a calibration routine for 5 seconds. During calibration pass a piece of filament back and forth across the sensor, and it will record the values that let it detect when the shadow is present.
While the winder is running in Auto mode, holding the middle button will let you use the knob to set the current position of the guide, and whichever direction it traveled to get to that point is the direction it will continue as the spool turns.
In addition to STLs I have provided the board and schematic for the electronics, and the gerber files I used to order the PCBs from OSHPark.
The base is laser cut, but the drawings could potentially be used as a template for using a saw and drill. Accuracy isn't that critical, and the tab-and-slots could be replaced by angle brackets. The drawing for the wood is forthcoming.
This will be offered as a kit through Filastruder.com, hopefully around mid-Nov depending on how long it takes to get the assembled electronics in.