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.

MakerBot Thoughts 2

I have ideas written on note pads and paper plates scattered everywhere I might have a thought. Again, I’m just going to post them here for myself and hope that others find some inspiration.

XYZ Platform
-Encoding. Phil from FUBAR Labs pointed out that we don’t necessarily need encoding along the whole range of each axis to do continuous printing via the belt method. We just need a way to determine when the nozzle is at the right height for each print. We might be able to do this using the endstops.

-Heat a thin filament and put it through an atomizer-like device to spray the material. Spray in layers to build an object. This probably doesn’t need to be a filament. This could be cool for a freeform fabricating lathe.
– I want to eliminate the thermal barrier retainer. We shouldn’t need a thermal barrier if we make a heater barrel with a thermal gradient such that the tempreture at the top never reaches a bad tempreture for the acrylic extruder body. We could have a captive nut in the extruder body that the heater barrel screws into. A few washers can be at the top of the heater barrel to act as a heat sink.
– Frostruder. There are decorating frosting tubes you can buy at most supermarkets. They have the basic shape of a toothpaste tube. If the back were cut off it would make a cylinder. This is pretty close to a pre-filled syringe.
– Instead of a flat-edge timing pulley as the pinch wheel, we might be able to use a pulley with a curved profile or a V profile. The pulley may not even need to be toothed if the filament fits in there right.
– Bowden extruder. Place an encoder at the heater barrel end to monitor the entering filament. A valve in the mechanism at the head can regulate the flow.
– the larger the pinch wheel and idler pulleys are, the more surface area they will have to contact the filament. More teeth in the filament means a lower force per tooth to achieve the same total force. We want to keep the force per tooth well below the shearing force of the material.

Slicing and Dicing
– During infill the extruder leaves gaps at the end where it turns around. The ends should be a dog bone shape to fill this in rather than a perfect U-turn.

– Let’s make a henna extruder! We can give ourselves temporary tattoos.
– Feed plastic ribbon into the extruder rather than a round stock. This could give more surface area for the extruder to grip. Maybe a triangular profile, which can fit into a V-grooved pulley. A triangle profile would probably work really in Zach’s twin drive extruder.
– Is there a glow in the dark material we can extrude?

Other Parts
– Use a capstan-like device for loading the filament.

– What is the shearing force per tooth on the pinch wheel and the twin drive extruders?

Macheining Notes
– To bore a hole through brass threaded rod to make a heater barrel I need to buy a “high-speed steel” bit. It should be “long length”. It’s okay if it’s parabolic.


As part of my Awesome August hacking I designed a slightly new extruder, the Paxtruder! This extruder is a derivative of Zach’s plastruder and I’m really excited to share it. The main difference is that exchanged the idler wheel with a Delrin plunger. This reduces the overall size of the extruder uses two fewer layers. See it in action.

Using a plunger allows the force exerted on the filament perpendicular to its direction of travel to be adjusted while the extuder is running. I mounted the electronics along the side, so I can view the teeth on the filament on the way to the thermal barrier and adjust the force to get the tooth depth I like.

With this design, changing the filament takes approximately ten seconds from when the barrel becomes hot enough. The motor can be removed with out disassembling the housing.

There is, however, a flaw in this particular design. The captive nut holding the plunger screw will crack the acrylic if you tighten things too much. In the next version I will have this fixed. This design is also based on a larger diameter timing pulley, so the filament guide is a little off.