Thursday, June 12, 2014

Big Red's Hot End

As the Seafair Milk Carton Derby approaches, work on Big Red is accelerating. Seafair's Milk Carton Derby is an event we participate in every year to highlight some of the potential benefits of additive manufacturing/3D printing. Participants in the derby traditionally collect used milk jugs or cartons and use them as flotation for rafts or boats. For the last two years, WOOF has participated by collecting milk jugs, grinding them up and using them as raw materials for 3D printing a boat on Big Red, our largest 3D printer.

I'd like to present different aspects of Big Red as the event approaches. Today, we'll take a look at the hot end/extruder. This is a great improvement over last years design in functionality and ease of use. First, the basics of the extruder:
The motor on the end is a 12V wiper motor, which spins an auger inside the steel pipe, driving the plastic down to the end of the extruder.
The heating element is wrapped around an aluminum pipe, with some insulation and another aluminum pipe on the outside.

The most significant improvement so far has been the modular heating assembly that we can pull off easily when changing which recycled material we will be printing with. We use the same heating element for PLA (compostable silverware) or HDPE (milk jugs), but switch out the steel pipe and auger.
The extruder tip is simply a pipe cap that we drilled a hole in. Actual hole size may vary.
And that's the hot end/extruder fully assembled.


  1. Hi Dana I have been following your blog since your first boat build and it's been a great learning experience I am coming up with a similar hotend to print directly from granules to use it for producing moulds for fibreglass fenders could you please guide me with some questions 1. What are the settings you are using in slicer I mean layer height and extrusion speed
    2. What size auger are you guys using ?
    3. Can I use a smaller size auger around 100-150 mm instead of a big one and drive it with a stepper
    I want to extrude around 7 mm diameter and with moderate speed it will be very helpful if you can give me some pointers
    Thank you awaiting your reply

    1. 1) We ended up using 3-4mm layer height. Our motor could only rotate at one speed, so we adjusted everything else based on that.
      2) Our auger was 18 inches long and 0.5 inches in diameter.
      3) You could use a smaller auger with a stepper, your stepper just needs to have enough torque to run it. Some calculations may be required.

      We had to make a lot of adjustments after test prints, with each type of material requiring different settings. You'll very likely have to do the same. You might take a look at the Filastruder, Lyman extruder, etc. for some ideas as you could basically strap one of those to your z-axis as an extruder.