I’ve been working on a small-scale plastic extruder to produce 3mm ABS filament out of small bb-sized plastic beads. The utility of this project should be obvious, I think, especially since the price of 3d printer filament has been climbing steadily over the past few months.
I usually find it useful to go over the ‘standard industrial practices’ of a build before getting my hands too dirty and investing too much time and effort. In researching plastic extruders, I came across this wonderful page that describes the inner workings of large, industrial sized plastic extruders.
The not-accurate, but still gives you a good idea pic of a plastic extruder.
Obviously, the most crucial parts here are an auger, long pipe used to heat and contain the melted plastic, a hopper, and a die. Plastic beads go in the hopper, are driven along the pipe with an auger, melted with heater elements, and extruded through a die. Easy enough concept.
Because this will be a ‘home-built’ extruder, the obvious place to get an auger is a simple wood-boring drill bit. The tip of a half-inch diameter drill bit can be ground off and will serve as a wonderful, if primitive, auger. One thing of note is a simple auger drill bit does not meet the criteria for an auger given in the above website. The above website specifically mentions a compression zone, where the channel depth between screw flights is reduced, compressing the melted plastic. No drill bit in the world has this, and it is something to remember.
I’m inferring from the website that a finely-tuned motor control system is necessary to produce a filament of a consistant size and shape. Because my greatest hopes are only to produce one 3mm filament at a time, speed control for the auger will be important. This means an h-bridge DC motor setup along with some sort of encoder.
ABS melts at around 230 degrees Celcius. for temperature control we’re going to need a thermocouple chip attached to an Arduino (might as well make it easy for myself), along with some sort of relay that can handle enough current to heat up a lot of plastic and metal.
Aside from the mechanics, it’s obvious that I’m going to need to electronically control a heater element and motor. Also, I’m going to need a thermocouple to read the temperature of the extruder, and some way to measure the speed of of the auger while it is rotating.
What I have so far
Boom. Hells yeah.
I’ve completed construction on the ‘core’ of my extruder pipe. It is built around 1/2 inch copper pipe – the same type of pipe you will find behind your sink and in the walls of your house. The pipe is wrapped in Kapton tape, a K-type thermocouple is attached to the end and nicrome wire wraps around the final 3 inches of the pipe.
I salvaged the nichrome wire from a hair dryer I found at a yard sale. Because I plan on using 12 Volts to heat the barrel, I needed a precice length of nichrome wire. The wire I recovered was 26 AWG. Plugging this into Ohm’s law, I needed about 26 inches of wire to provide a resistance of 5.7Ω. I’ll be drawing 2 A – and 24 Watts; a small enough value so that a standard wall wart can be used to heat the barrel. With 12 V, I should be able to get this pipe up to about 300° C. The leads for both the thermocouple and nichrome are insulated with Kapton tape.
I know using copper (especially soldered-together fittings) isn’t extremely smart seeing as how I’ll be running this extruder at about 230° C. I have a solution to this problem, updates pending.
This is what I came up with in a few hours with AutoCAD. I plan on driving this with a belt and a DC motor; the second notch at the end will be where that will go. Yes, there is a ‘compression zone’ for this auger, so the only obstacle now is finding a 4 or 5-axis mill.
Future updates to come, I’m sure.