BB-14F (Bear Extruder-mod)

This is a (partial) remix of the Bear Extruder for use with the Prusa MK3, which makes use of a BMG shaft/axle and a NEMA14 round pancake to create a geared printhead with a much lower weight.

Replaces the body & idler-door from the Bear Extruder, the rest of the printed parts from the Bear Extruder remain the same.

Don't forget to share a make! ✌

Weight comparison

* The weights include the motor(/+gearbox), extruder body (with screws etc), filament sensor & bondtech gears. Things like fans and v6 aren't included in here.

Necessary hardware (BOM)

Notes

There is a mechanism to slightly vary the gear meshing. Play around with this to get a nice mesh. An ever so slight backlash is better then the gears being too close.

Gear ratio = 5:1

“Firmware changes”

For this mod on the MK3, make a .gcode-file with the lines below (put it on the SD & run on the printer), or run these over an USB-connection.

If needed, to revert back to stock MK3(S)

Motor current!

Depending on the specific NEMA14 you get, it may need to be run at a way lower current than the stock motor. Otherwise things can get heated real quick! Stock currents can easily get some motors over 100c, which will melt the extruder body or worse. The necessary current will depend on your motor.

E.g. I've found the LDO-36STH17-1004AHG needs to be kept below 300mA, where less still probably would be better.

Slicer/firmware changes

For stock MK3 firmware, the current can be specified through the slicer. To change this, in the “Custom G-code” section of the slicer, edit the lines where it says not to change them 😄

Start G-code

Replace these lines

; Don't change E values below. Excessive value can damage the printer.
{if print_settings_id=~/.*(DETAIL @MK3|QUALITY @MK3).*/}M907 E430 ; set extruder motor current{endif}
{if print_settings_id=~/.*(SPEED @MK3|DRAFT @MK3).*/}M907 E538 ; set extruder motor current{endif}

With (replace E250 with the current needed for your motor)

M907 E250 ; set extruder motor current

End G-code

Remove this

{if print_settings_id=~/.*(DETAIL @MK3|QUALITY @MK3|@0.25 nozzle MK3).*/}M907 E538 ; reset extruder motor current{endif}

You can now save these changes as a new printer profile. Give it a descriptive name so you can clearly identify it. When your current is lower then stock: make sure you are using the resulting printer profile at all times for the printer(s) with this upgrade!

Trivia

BB-14F = BearBMG-NEMA14Fusion

Credits

It's a remix of the BearExxa as created by Grégoire Saunier. Based on the 1.0.0 (BearExxa) source files.