Compact Bowden Extruder for Creality Ender-3 and CR-10

Customized for Creality Ender-3 and CR-10

Benefits:
* adjustable pressure
* increased filament dosing accuracy by 44%
* reliability

Necessary changes in "configuration.h" for Marlin firmware:
* "#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 400, 144 } // default steps for extruder = 144 steps/mm"
* "#define INVERT_E0_DIR false"

BOM:
1x MK8 hobbed pulley
1x PC4-M6 push in fitting
1x 608zz bearing
1x M5x10mm half-round head screw
3x M3x8mm allen head screws
1x M3x16mm allen hea