Hercules Extruder

When I began working on an extruder, I spent quite a bit of time working on a screw based drive, attempting to engage the plastic in order to push it into the heater barrel. Turns out – plastic is slippery. I’ve seen lots of problems with screw based extruders, so I looked into using a pinch pulley. It works beautifully!

There are a few nice side effects of the pulley – The extruder is very simple, doesn’t require much fabrication, and can be reversed instantly to stop plastic extrusion (there are no plastic fuzzies). Unfortunately, since I use a stepper, this extruder cannot be directly used by the reprap firmware without modification. I’m currently refactoring the reprap firmware to enable device abstraction which will allow either a stepper or dc motor.

Hercules Extruder

Hercules Extruder

Download Sketchup

The heating element is 8 inches of insulated nichrome wire, purchased from RepRap Research Foundation wrapped around an 1/8 inch brass plug. The brass plug was turned to a point (or filed to a pyramid). A .01″ hole was drilled in the tip (very carefully!). The brass plug is threaded using a 1/4″-28 pitch tap. (The brass plugs from home depot are hollow, so it is easy to tap; otherwise it needs to be drilled out).

This is a previous implementation with a brass coupler. The extra brass was acting as a heat sink which was causing problems keeping the extruder up to temperature.

The extension barrel is a 0.375″ OD x 0.12″ WALL x 0.135″ ID T-316 stainless steel tube from Online Metals. Half inch of the tube was turned down and threaded to mate with the heater element. I’ve been asked what the resulting heating characteristics are of the new barrel – I’m happy to say that the brass element holds temperature well, and the stainless does not conduct much heat (the top barely tops out at 115F)

The Sketchup presented differs slightly from the implemented extruder. This was simply due to resource limitations (material on hand). The Sketchup includes a better mounting bracket for the heater barrel and uses a single piece of aluminum for the mounting wall.

Herk? Before my father retired from the Air force, he flew a C-130 transport nicknamed Hercules. He currently uses the name “Herk” as his handle in various games. I named the extruder for him as a small form of thanks.

10 thoughts on “Hercules Extruder

  1. Thanks for posting this.
    Using brass inserts is a good idea — good conductivity and widely available!
    I like the idea of abstracting out the specific actuator types (stepper vs brush motors.) I encourage you to post a link on the reprap forums: http://forums.reprap.org/index.php

    Note: a sanguino has more I/O pins, and might make this easier to control along with three other motors for the axes of a cartBot.

    — Larry

  2. Hello Larry,
    I’ve got my Sanguino partly built on my workbench 🙂

    Zach (original author of the arduino firmware for reprap) has a preliminary discussion/specification for the refactor. I’m developing a desktop emulator which will allow me to test the major subcomponents prior to uploading to the arduino. This is going to be a lengthy process because I don’t have a working ‘standard’ reprap, so I need to ensure compatibility while enabling the actuator and extruder abstraction.

  3. You’re going to run out of pins on a standard Arduino. I have been talking to Simon McAuliffe about resurrecting the I2C concept – nice and easy to implement, I/O expanders available off-the-shelf and Arduino support already provided.

    Vik :v)

  4. Design looks nice and small compared to the large monsters that are out there right now. These machines take up way to much room to have much practical purpose anymore. The industry really needs to start shrinking the machines so companies can have more bang for their buck when it comes to the floor room in the manufacturing area. Take a look at this site, this company is making everything much smaller and a all in one digitial system. You may want to present this idea to them. http://www.monolithicindustries.com

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