Summary

3mm Direct drive extruder compatible with Prusa Mendel and similar printers.

Instructions

I have now succesfully used this extruder with a DIY drive gear. The parts have been upgraded to have a stiffer filament compressor arm and a fully supported stepper shaft (I bought 20 of these bearings so why not).

My calculated steps per mm (132.285) are pretty close but I still need to calibrate it (It's late and I'm tired). I'll post some examples once it is fully calibrated. The one test piece I have printed looks to have the same quality I have come to expect.

Run it in reverse and it can be used as a bowden extruder. The filament runs through 1/8" teflon tubing threaded into an M5 nut which is held by the nut trap.

For this extruder you'll need:
M3x12 screw x 3
3/4" 4-40 screw
1" 4-40 screw and nut x 2
625z bearing x 2
*#10 brass or steel spacer, 5/16" OD, 3/8" Length for the drive gear.

Assemble as shown in the photos. The extra hole and nut trap on top is for a filament guide attachment.

You may need a 3mm ID 5mm OD spacer for the compression bearing. It just so happens that my 4-40 button cap screw fit right into the bevel inside the bearing enough to keep it centered but would not go all the way through so the spacer was not necessary.

The assembly is easy and I'm sure the photos are enough for you to figure it out.

To make the drive gear:

A drill press comes in handy but is not necessary.

Hob the #10 spacer as shown in the photos, placement of the hob is not critical since you can easily adjust its placement just make sure you have enough room for the set screw. Drill and tap one or two holes like in the photos. I used 4-40 1/8" set screws. Finish by drilling out the spacer with a 5mm bit so they will fit on the stepper.

A note, I didn't use any of the gears shown in the photos. I ended up making one that was cut more shallow than those. I only hobbed it enough to get good teeth in the brass. I used a 6-32 tap.

Since I am running 3mm filament through a 0.35mm nozzle a great deal of torque is needed to have reliable extrusion and in order to get more torque you need more amps. I added a larger heatsink to my extruder stepper controller to ensure it stays cool. After about an hour of testing the extruder the stepper was pretty warm so I plan to add some heatsinks to the stepper itself.

The printer you see in the photos is my HaMendel printer. My last name is Hamende (Ham-end) so putting Hamende and Mendel together I got HaMendel. I designed and fabricated it myself with some inspiration from the mendel. It has a full 200mm z height with 12mm z smooth rods and 10-24 leadscrews. This means ZERO z wobble. The two plate design keeps the whole thing incredibly stiff. I will eventually add this to thingiverse but it will take me some time to get all of the part files together.

3mm Direct Drive Extruder / Bowden Extruder