Print 3D

Edit:24 févr. 2021, Cre:28 mars 2016

Direct extruder

Preliminary note

Even with high torque large stepper, this direct drive extruder was never as efficient as the nice geared extruder I designed for the Fisher and am still using on the Lily. This is not only related to the geared transmission but I think the small hobbed drive from the Fisher Delta is better than other stuff and the better traction may also be related to the smaller counter-bearing. This direct drive was replaced by a nice full aluminium clone of the dual drive BMG. This page shall be considered as history and is left there as such but I removed the internal links.


For the D-Box, I developed in OpenSCAD a Bowden direct drive extruder to be mounted sideways on panel.
Then I designed other mount types: On panel face (Fisher style) and on rod.
There is simple and double extruder version.
The antivibration support efficiently prevent the transmissions of vibrations to the panels.

Miscellaneous mount types

An optional filament guide allow installation of a sponge and filament detector (on panel side mount only).
Lever articulate directly in supports without any metallic part
This design is not really original but it minimize the fittings required.
This extruder is now an option for the Lily boxed delta printer design (larger versions).
It is practical for a boxed printer as extruder is outside the box, but could be used for any other printer type.

It is for filament 1.75mm and guide filament as close as possible to the hobbed insert, allowing easy change of filament while printing.
This may help somewhat with semi-flexible filament, taking into account the difficulties associated with bowden tube.

The philosophy is to have the minimum parts and articulation is directly printed
After testing miscellaneous pushfit ends for the bowden tube, a simple M4 nut was chosen as the simplest and most effective way to lock the tube. There is no quick bowden disassembly however this is more needed on the hotend than on the extruder.

As with all direct drive extruders, you shall use a stepper motor with large torque, say 5.5~6.5 The larger, the better.
Don’t use low current steppers as they have high inductance and cannot rotate fast. For a Bowden tube extruder, you need fast retract (150~200 mm/s). Minimum nominal current of the stepper motor shall be 1.5A.
Low diameter MK8 hobbed insert allow reasonable force for a direct extruder, but you shall buy a good quality one, specially designed for 1.75mm filament. Hobbed insert bi-compatible 1.75/3mm have a poor grip.
The tensioner shall not be overtightened, that reduce the available torque. Just tight sufficiently to not grind the filament and skip steps.

The optional guide plate allow to install a cleaning sponge, and there are planes to screw filament presence switches.

Bill of Material (BOM)

Components :

  • 4 Screw/bolts diam 4 for panel attach
  • 2 countersunk head bolt M3×15 with washer M to attach filament guide to extruder base
  • 2 countersunk head bolt M3×10 to attach extruder base to antivibration support

for each extruder :

  • 1 hobbed insert MK8, stainless steel, SPECIFIC for 1.75 mm filament - don’t use ‘bi-compatible 3mm-1.75 mm’
  • 1 bearing 695ZZ (13×5x4)
  • 4 screws M3×8, countersunk head, for motor attach
  • 1 bolt M4×30, hex head, with butterfly nut and washer M; for tensioner
  • 1 bolt M4×20, countersunk head, with washer M; for bearing
  • 1 nut M4 for bowden locking
  • 1 spring dia 8 x wire 1mm
  • Bowden tube.

Printed parts

even reference: non-mirrored (left panel) odd reference: mirrored (right panel)
parts to print:

  • 1 extruder base double: 2,3, simple:8,9, face panel:16.17, on rod:18,19
  • 1 antivibration support double: 4,5 simple: 10,11
  • 1 filament guide double,reclined:6,7 simple,reclined:12,13, simple,vertical:14,15
  • Alternatively to filament guide, if there is no need for filament detection, you can print a simple sponge box : 20

By default, the bowden shall be screwed in a M4 nut. If you want to install a pushfit, you have to tap the lever. Prefer M5 thread as it is easier to tap than imperial thread, and on PETG, you could use an ordinary screw for tapping.

for each extruder:

  • 1 lever: M4 nut 22,23 Pushfit (drilled 3.8 mm): 24,25
  • 1 tensioner: 30
  • 1 thumbwheel: 32 (option)
  • 1 spool spigot: see spigot.scad - length is adjustable - supplied stl with 90 and 95 mm length

Note that the thumbwheel tend to slip if there is no flat on stepper shaft. Also, the thumbwheel prevent easy disassembly of the lever.

Recommendations for printing

  • Use a calibrated machine to have accurate dimensions
  • Use material resistant to temperature, ABS or PETG
  • Fill in: Honeycomb, 75% , layer 0.3mm 5 full layers on top and bottom, no support
    Note that printing in layer 0.3 gives stronger parts, so don’t be tempted to print in thinner layer for precision, which will not be better, anyway.
    Note that fill in shall be ‘full contact’ between the layers, so, for some slicers, honeycomb may be replaced by ‘triangle’. DON’T use rectilinear infill, except for 100% infill. 100% infill will not be longer to print, it will just use a bit more filament.

Assembly recommendations

Assembly is straightforward, however, you need to stop the bolt to install sprint and nut, use a screw driver.
Take care to well align the hobbed insert with the lever.

The M4 nut is the most reliable method to attach the Bowden tube, however it is not easy to disassemble. This type of mount is only possible if you can easily disassemble the Bowden on the hotend side (which is most often the case).


STL files and OpenSCAD program are available on GitHub
All my OpenSCAD realisations are shown here

© Pierre ROUZEAU Jan-March 2016
files in :

  • Part licence : CERN OHL V1.2
  • Program license GPL2 & 3
  • Documentation licence : CC BY-SA
(c) Pierre ROUZEAU
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Page mise à jour le 24/02/2021 13:09