10/5/2019 Update: The gearbox has been redone from the ground up, now supports motors with longer shafts like the LDO .9 degree pancake stepper without having to cut the end of the motor shaft off.
9/3/2019 Update: Made a few optimizations to strengthen a few areas, especially for the hex nut version as a tester had the edge crack. For hex nut version I have made the hex nut cavity a little larger and added some additional plastic to reinforce the hext nut pockets. I recommend using the heatsert version (it's what I use), but if you decide to use hex nuts this new update should be better for you.
I really loved the "Bunny Science Extruder Motor Gearbox" by BunnyScience. I used it for a while with a few minor modifications but BunnyScience moved on to making complete extruders so I wanted to make some additional refinements. This mod works effectively the same way but there are some changes in the design to slightly improve (per my opinion). I also really liked the look of knoopx's design but on my extruder the gearbox interfered with the hotend fan.
Changes from Bunny Science Extruder Motor Gearbox
- Better optimized for 3d printing, prints with no supports and the geometry should print using bridges instead of sloped overhangs.
- Less plastic making it 30% lighter (19 grams vs 27 grams)
- I'm using this on a bear extruder, and a bear extruder is happier with chamfers instead of fillets :D
- The BunnyScience design belt was a little too tight for me and the 16T pulley had to be almost right on the motor to prevent the belt from rubbing, I moved the motor out a little to allow more room here.
- I just think it looks better, but this is just my opinion.
Materials (This is basically the same as the BunnyScience gearbox)
Assembly is basically the same as the Bunny Science gearbox.
Prusa FW Settings
For 1.8 degree stepper you will want to use 1/16 microstepping on the E axis, for a .9 degree stepper motor use 1/8 microstepping. And with both you would want to use 490 esteps
M350 E16 ; sets microstepping to 1/16
M92 E490 ; sets esteps to 490
M500 ; save to eeprom
You can verify your current settings by issuing
7/19/2019: I had a situation where my 870 PLA Skelestruder wheel broke, I'm sure it's because I over tightened it but I decided to remix it to beef it up a little. I also recommend printing this part in PETG now as well.