The puller controls the speed of the filament coming into the winder, and isolates the tension created by the spool from the extruder. It’s run by a 37mm 15 rpm gearmotor, mounted by 2 M3x12mm screws.
Print the puller mount, and drill the holes so that they are the correct final dimensions. Use a 3mm bit for the two holes at the top edge, and the holes for the motor, which are a little above center. On the back drill the top two holes a short way in with a 6mm bit and push some M3 nuts in.
Print the two extruder pieces, and clean out the support and trim any wayward threads from the bearing holder. The 625 bearing should snap in and spin freely. Use a short M5 bolt to hold it in place, but don’t use a nut. Take care that the bolt does not extend from the back, or it will cause the holder to twist away from the mount.
Screw the base part of the extruder on to the mount with a M3 18mm bolt. Ideally the head of the bolt will hold the part snug against mount without sticking out the back where it will get in the way of the motor. Use some washers on the front if the bolt is too long. Attach the bearing holder with a bolt long enough to go through both pieces and the mount. Cut a section of spring about 10mm and wrangle it into the recess on the base part of the extruder. Tweezers might help here.
Print the two halves of the tension wheel and glue them together. Push a 608 bearing in through one side as far as it goes. Put a M8 bolt through the larger hole of the tension arm, add a nut, and slide the wheel up against the nut. Tighten another nut against the other side of the bearing in the wheel.
The potentiometer has a little tab that sticks out to keep it from spinning in its mount. You will need to drill a small hole in the mount next to the hole for the shaft to accomodate this little tab. Put the shaft a little ways through the first hole and slide on the nut that came with the potentiometer before pushing it the rest of the way through the second hole. Use some tweezers or skinny pliers to screw the nut onto the threads on the potentiometer shaft. It’s tricky, but you should be able to get it in a minute or so.
Turn the pot back and forth until you have it near the middle of its range of motion, and press the arm onto it. Position the mount alongside the wide part of the motor with the wheel lined up with the upper filament guide hole and screw it down to the board.