The overall design is the same, but I remodeled the body from scratch.

Main Differences from Foehnsturm's design. (1) changed hot end mount to UBIS (2) slightly increased angle of motor mount, to give more room for cooling (3) enlarged gear box to accommodate a wider variety of worm gears. (4) increased gear box shaft to 5 mm. Bearings are still 10 mm OD.

For the motor, I recommend 0.8A rated Nema 8 stepper, though you can make a 0.6A stepper work. I got good results from running 1/4 steps at 1553 steps/mm. At 0.6A you might be able to get away with not putting a fan on the stepper motor. At 0.8A something seems needed. I used a crossflow fan that blows across the top of the printer.

I highly recommend printing the part from PETg or a more heat resistant material. PLA will soften too much from exposure to the motor and hotend.

You can get the pressure arm file from Foehnsturm's design. You may need to trim off material, if it interferes with your worm gear. https://www.youmagine.com/designs/modular-printhead-nema8-worm-gear

Changing filament is easiest when you use a pair of adjustable pliers to squeeze the pressure arm. Do not pull against the motor when doing this.

After printing the main body, use a hard epoxy to fill in the rectangular divot at the top of the main body that the spring bears against. This will keep the spring from tearing up the plastic.

On the 2 mm screw that runs past the mk8 filament drive gear, you will need to grind the threads off the bottom half to make clearance for the mk8 gear.

You should use aluminum foil or similar to shim up one side of the motor, to adjust the contact between worm and worm gear. When done correctly, the worm should be able to rotate with very little resistance.