Wade's Geared Extruder

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Revision as of 20:10, 17 August 2010 by Casainho (talk | contribs) (Added a kind of promotional video for this extruder ;-))
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Wade's Geared Extruder

Release status: Stable

Geared Nema 17 Extruder
CAD Models
External Link

This extruder works for RepRap Mendel and is robust, provides a strong force to extrude, is cheap and DIY. It is an alternative to the standard extruder for RepRap Mendel and have the following advantages:

  • no need to buy/use expensive metal gears;
  • no need to do two precision flats on motor shaft;
  • no need to glue the PTFE barrel;

Other advantages over other extruders are:

  • extrude/print at high speed;
  • good for use with a low torque/cheap Nema 17 motor;
  • no need to use expensive and complex tools - just one hand drill, a file and a M3 tap;
  • no need to make splines on motor shaft;

See this extruder in action (video recorded by Casainho on 2010.08.18): <videoflash type="blip">AYH2oxYC</videoflash> View the high quality original vorbis video file.

View photos on Thingiverse from other people's copies of this extruder.

Buy it: If you can't make yours or simple if you do no want, you can always buy one. There are users printing it and selling on Ebay.

Mechanical Construction


Non printed parts:

  • 3 X 608 bearings (Skateboard bearings);
  • 1 X M8X50 bolt;
  • 1 X M8 nut (Nylock works better, but a pair of nuts will also work);
  • 4 X M8 washers;
  • 1 X M8X20 piece of smooth bar, threaded bar or a bolt;
  • 4 X M4X45 bolts;
  • 4 X M4 nuts;
  • 4 X M4 washers;
  • 4 X M3X15 bolts;
  • 2 X M3X35 bolts;
  • 8 X M3 washers;
  • 4 X Springs - 1 mm diameter wire, wound to an OD of 10 mm, with 4 active coils. For a given filament drive force, you'll need about twice the spring force - ie, if you want 100 N of filament drive, your springs need to push with about 50 N each. NOTE: some users have theirs extruders working perfectly without this springs.
  • 1 X Nema17 StepperMotor

Printed Parts

  • 1 X M8_Extruder_Block_3.stl
  • 1 X M8_Extruder_Idler_Block_2.stl
  • 1 X 11t17p.stl
  • 1 X 39t17p.stl

How to build it

I used a hand drill and a file to cut the slot, then hobbed it with an M3 tap mounted in the drill, using bearings mounted in a vise to let the bolt spin - see the next videos. If you're not sure where to cut the pinchwheel slot, test assemble the extruder, making sure you leave room for the motor mount bolt heads under the 39 tooth gear, and mark the M8 bolt where it crosses the filament feed channel.

Filing the shaft: <videoflash type="youtube">2FU0v-3gloo</videoflash>

Using M3 tap: <videoflash type="youtube">Hl4Gf5R4YJg</videoflash>

M8 1.jpg

This is an earlier version with using threaded rod - it's harder to get the hobbing concentric when you cut it into the threads.

M8 2.jpg

Using the smooth part of a shoulder bolt works better.

M8 2inside.jpg

Note - I prefer to use a Nylock nut on the end of the M8 shaft. Locktite should work as well, or a longer bolt with two nuts.

M8 2gears.jpg

So far so good! If you add 3 or 4 M4 washers on each bolt before you put the idler block on, it will reduce the idler block travel when loading new filament, making loading new filament much easier.

Here's the test jig:

M8 test jig.jpg

This extruder hit 16 kg - here's the results: M8 shoulder bolt - 7.0kg, adjusted tension, new springs - 11.0 kg,

Tightened springs, 3 trials:

15.5 kg, 16.5 kg, 15.25 kg

The final failure mode was the stepper running in reverse, as opposed to the filament slipping. That's quite promising.

Hot End

Attach a length of 16 mm OD PTFE using the two M bolts to pin it in place. I pre-drilled the PTFE mounting holes with a 2.3 mm drill, which made for a tight friction fit.

The nozzle can be built however you like; I build them similar to this: http://reprap.org/wiki/Mendel_extruder

I use 8mm od brass rod, with a 4 mm ID melt chamber, insulated nichrome wire and furnace cement to hold it all together.

3D CAD Files

Here's the design files for the latest version:

Finally, here's a spreadsheet to help calculate the proper feedrates: media:feedrates.ods | media:feedrates.xls

An updated version of the spreadsheet to use with Skeinforge, somewhat simplified. I vary the layer thickness, width/thickness and the two speed settings until I get a density near unity for nicely solid solid parts: media:Extruder Calcs 2010.07.13.ods

Older versions

Here is a link to a previous version of this page that describes an earlier version of this extruder that uses an M4 shaft, and includes more details about pull testing the two versions: "Geard Nema 17 Exteruder Version 0.5"