I’ve updated the Paxtruder-0.1 design to address flaws and make enhancements; I present Paxtruder-0.2. After a few more prototype iterations I should have a nice upgrade kit available for those who would like to experiment with various size filaments and multiple extruders.


Improvements from version 0.1 to 0.2

  • The captive nut for the thumb screw is held in place by two screws rather than acrylic, which cracked.
  • The thermal barrier retainer has been removed. This means fewer parts.
  • Fewer unique parts. This method of pressing the filament against the timing pulley requires only three layers. However, a fourth layer is necessary with this motor due to its neck. Since one layer is only a spacer, I made it identical to the retaining layer.
  • A 606 bearing is used as in the Plastruder MK4.

Advantages of the Paxtruder over the MK3 and MK4

  • Fewer parts. No thermal barrier retainer, no bearing, no idler wheel, and four layers rather than six (needs only three, but may become as low as two). And all those nuts and bolts we don’t need. You can see how few parts are used in the image below.


  • One thickness of acrylic is used for all parts rather than three or so in the MK4.
  • Reduced filament replacement time. You no longer have to wait for the MK4 drive mechanism to screw your filament out and back in. Just loosen the thumb screw, pull out the filament, put it back in, and tighten your thumb screw. A ten minute job becomes six seconds!
  • Filament pressure can be adjusted while building. No tools necessary!
  • It’s smaller. You can fit two extruders in one MakerBot. Wow! Imagine a second extruder on the left of the platform in the image below.


  • Other filament sizes work. You can use the same extruder with different sized filaments. I use mine with the standard 3 mm filament and I’ve also been experimenting with a 0.07 inch filament. This will work with any filament smaller than the layer thickness of the acrylic. You will, however, want to use a bore diameter for your thermal barrier and heater barrel which is appropriate for your filament diameter.
  • Small enough to be printed without worrying about the edges popping up. Anyone want to convert this to a 3D model?


  • One more material. The part that pushes the filament against the timing pulley is Delrin. It’s not expensive, but it’s one more thing to order.
  • The motor has to work harder (I think). I haven’t tested the additional friction force resulting from the Delrin because it hasn’t been a problem, but it’s got to be something greater than zero. I think the friction force may be negligible.
  • The Delrin will wear out. Some have expressed this concern, but in my tests it has not been a problem. The ABS does not wear away the Delrin and the Delrin does not wear away the ABS. The image below shows the Delrin surface in contact with the ABS after approximately five hours of printing with 3 mm ABS.


The future

  • Use a stepper motor.
  • Use two layers. A stepper motor with a flat face and no neck will mean the Paxtruder only needs the layer where the Delrin lives and one layer to hold it in place. The stepper motor will act as the other side of the Delrin sandwich. This should make machining a Paxtruder from a solid block easy; it would need only two milled paths and a few drilled holes.
  • Bring the thermal barrier closer to the pulley to reduce the space where the filament can bend.

13 thoughts on “Paxtruder-0.2

  1. Great idea! If you sell it as a kit, it would be a good idea to include some extra Delrin in case one breaks.

  2. wow this is great! I’ve been struggling with my plastruder and this is a welcome change!

    are you planning to sell this as a kit? i’d love to buy one from you and be your guinea pig to test it out in the wild, (if you need one).

    1. I expect to have a kit available in the next few weeks. I have a few days off from work next week, so I should be able to get a lot of work done then. When it’s ready I’ll make a blog post.

  3. I too would be interested in a kit. I am
    missing the plastruder to finish off my

  4. Indeed, I broke my plastruder by extruding too close to the platform. The brass parts unscrewed and fell, dangling and rattling.

    Your plastruder is an example of good design except for one thing… the bottom part! I have some spare PEEK and a CNC mill w rotary axis. If you want let me know how you would use them to replace the thermal insulator and the metal disk etc. And how you would adapt the acrylic part to mate the peek etc parts. I’ll mill them 🙂

    1. A 3D model would be great! You might want to hold off for a few weeks, though because I’m making a few small design changes. However, if it’s easy for you, it’d be cool to see the model on Thingiverse.

      Seeing the interest in this extruder is really exciting and motivating me to get a kit out the door.

  5. I gotta say, I like the look of this design!

    Have you considered putting up your designs right away on Ponoko and letting people buy them that way? That’d let you start selling immediately without infrastructure, and the only missing bit (the delrin) you could post out yourself.

    Does this design use the stock makerbot motor? I don’t remember it having so many holes for mounting bolts..

    I’d love to try this if it were either printable or immediately available! I’m considering printing a Printruder soon and testing that, too. I like how diverse the community’s approaches are to Makerbot design.

    1. I’ve nevered used Ponoko, but I’ll look into it. I’m not sure how I’ll distribute the kit.

      The Paxtruder is designed to be compatible with existing makerBot parts. In fact, the kit will be a mod kit for the Plastruder MK4; using the same motor, timing pulley, etc. This is to keep the cost low and get the Paxtruder to as many experimenters as possible.

      This weekend there are hackathons happening at a bunch of hacker spaces. I’ll be at NYC Resistor working on this. I still have the goal of making this available before the end of November.

  6. Hey Charles,

    Hey I was wondering why I have so much trouble with printing this extruder 🙂 I use Corel Draw X4 open the DFX File and select Metric. I then get something like this:

    I am not quite sure on what files I need to print and what are just “instructions” etc. Do you use Corel Draw to open these? Do you have the same issues?

    1. It looks like you’re using the 0.4 version. It’s a bit jacked up looking because I’m not quite done. The extruder is done, but the mounting bracket has been giving me a hard time. I’ll be at NYC Resistor for our meeting tonight, so I might be able to finish the design today.

      Corel Draw has also been giving me trouble with DXFs made in QCAD. When the design is done I’ll do an SVG export of the layout. This technique has worked well in the past.

      I’ll make another blog post in the next few days announcing the final Paxtruder-0.4 design and files.

  7. Charles,
    It looks like you were thinking of putting together a Paxtruder kit at the end of last year. Did this come to pass? I’d be interested in purchasing a kit. Please let me know if you’ve put one together.

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