A streamlined direct drive bowden extruder for 1.75mm and a MK8 design hobbed pulley. The OpenScad is nearly fully parametrizable, therefore it could be fixed to suit other pulleys that are hobbed also. The mounting plate may be taken out from OpenScad easily.

I've used a 13x8mm, 5mm bore brass hobbed because it was not difficult to get here in Germany.

The used MK8 design hobbed pulley may be purchased in the subsequent websites:

Note: I purchased an acceptable compression spring after, therefore it is not observable on most of the pictures.

UPGRADE 2015 03 17: Upgraded idler for better MK7 drive gear support
UPGRADE 2014 11 13: Added press-appropriate bowden inlet choice
UPGRADE 2014 09 22: Fixed OpenScad file due to non-manifold vertexes between foundation and filament tunnel after review with MeshLab, exported STL
UPGRADE 2014 06 01: Removed the work in progress flag after extensive testing and positive feedback from the community.
UPGRADE 2014 04 27: Set foundation and idler "printer ready" beneath each other, additional compact_direct_drive_extruder.stl with foundation and idler joined
UPGRADE 2014 04 07: Replaced tensioner hole with slot on idler, added funnel on bowden side of foundation for simpler filament insertion
UPGRADE 2015 03 17: Upgraded idler for better MK7 drive gear support
UPGRADE 2015 10 13: Designed choice idler to solve breakage of bearing support


  • Significant: If you are not using the same 13x8mm drive gear as I do, fix the drive gear measurements in the OpenSCAD file and export idler and foundation as different STL files.
  • Select appropriate variant: standard inlet or press-appropriate bowden inlet
  • Piece version and print idler and foundation plate individually. I utilized Slic3r with 0.2mm layer depth and a 0.5mm J-Head nozzle.
  • Use 2mm drill to wash filament course on foundation plate.
  • Use M5 screw tap to cut screw thread for push-appropriate bowden connector on bearing holder and base plate on idler.
  • Attach push-appropriate bowden connector(s) on foundation plate.
  • Attach 608zz bearing to idler and fix it with a M5x10mm allen head screw as well as an M5 washer. Should you be employing the alternative idler fix it with a M5x14mm allen head screw and add the 608 bearing between idler parts.
  • Attach NEMA17 Motor with three M3x8mm allen head screws (use countersunk holes).
  • Attach idler to base plate with allen head screw that is M3x16mm. Avoid to much tension to permit idler going freely.
  • Fasten hobbed on NEMA17 stepper motor shaft. Fix its height properly.
  • Fit Filament into extruder.
  • Add M3 nut into foundation plate slot.
  • Use M3 allen screw with washers as well as a spring to use pressure on filament of appropriate length.
  • Joyful extruding ;-)

What you require

Components used (BOM):

  • 1x foundation plate (printed)
  • 1x idler (printed)
  • 1x hobbed pulley 13x8mm, 5mm bore or similar
  • 1x M5 press-appropriate bowden connector (5mm screw thread) for 4mm OD bowden tubes (add another one for bowden inlet version)
  • 1x 608zz bearing
  • 1x M5 washer
  • 1x M5x10mm allen head screw (M5x14mm for altenative idler)
  • 3x M3x8mm allen head screws
  • 1x M3x16mm allen head screw (M3x20mm for choice idler)
  • 1x M3 nut
  • 2x M3 washers
  • 1x compression spring 3mm ID
  • 1x M3 allen head screw with appropriate length for the chosen spring

    Tools used:

  • M5 manual screw tap
  • 2mm drill
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