I’ve uploaded simple sprocket tool for rewinding Zim filament spools to Thingiverse. You can find it here: Filament spool winder
I recommend printing on the fast setting. The standard quality setting seems to throw the hole tolerances off on my Zim. It still works, but the pins are really tough to get in the hex holes on the sprockets.
Before using this thing, there is a sleeve printed on one of the pins that is designed to spin freely. Insert the pin in the sprocket, grab the sleeve with a pair of plyers, and then break the sleeve loose so it spins freely. Insert the other sprocket pin in a drill, and refill away. Be sure to run the drill in the right direction (if the drill is on the right as shown, run in reverse to ensure the filament is coming off the spool the same way the original did).
Sprockets
Sprocket on spool
Drill
To pop the top off the spool, squeeze the sides until the tabs start to pop out and work your way around the spool. Removing the spool top
Also, I’ve been experimenting with not putting the cartridge back together after refilling. Just putting the plate with RFID tag in and setting the spool on top seems to work so far. Cartridge loaded
Go to /cartridge/right (or left) to reset the refillable information, color, length, etc.