Sunday, February 28, 2016

Filament extruder: creating my own filament


A filament extruder is a device that melts plastic granules to make filament for a 3d printer. When I started this project, 3d printer filament here in New Zealand was rather expensive. And because I like to tinker, I build an extruder.

Plastic granules are about usd$5/kg, so the filament the extruder makes is quite cheap. Sadly you have to buy quite a lot of material to build a extruder. I never added all the cost, but would guess I spend around usd$100 on it.

It did take me quite a while to get nice filament out of the system. It is but still not finished. I still need to find a way to remove the last occasional air bubble in the filament. Also I like to automate the filament diameter control. Just ordered the parts for an optical filament diameter sensor. This allows for an automatic filament measure and control system so I don't have to monitor and adjust the filament diameter manually.

The base principle of a plastic extruder is very simple:

  • A motor drives an Archimedes screw pump that transports the plastic granules and creates a lot of pressure.
  • A heating elements melts the plastic
  • The plastic glup is pressed out of a small diameter hole.

But there are a lot of details that make or break an extruder. Some things that need attention when designing an extruder.

  • Use a lot of back pressure to remove air from the melt.
  • The melting temperature must be a low as possible , otherwise the plastic is to thin and not enough pressure can be build up.
  • As stable melt temperature as possible. Any deviation here creates filament diameter changes.
  • Use a winder.
  • Use a strong high torque motor and cooling for it.
  • Filter the molten filament to remove any junk.

At the moment I only have used Chi Mei  polylac Pa-758 plastic.  This is a clear ABS plastic. I started with this, because you can see any junk or air bubbles in the extruded plastic. This plastic has a MFI 3 at 5kg 200deg C that gives about 1kg/10hours in the current setup.
In the future I am planning to try other plastic types like natural abs, nylon and maybe even PC (polycarbonate),

Here some pics of my setup.


On the far left a box with electronics: (nice enclose is on the wish list too)

  • Standard PC power supply delivers 12v.
  • Temperature controller for the nozzle
  • Motor speed controller for the filament puller.

On the left a standard wiper motor drives the wood drill . The spiral wood drill is used as pump. Real extruders have a special shape of the pump, that allow for much higher pressures, but they are not available.
In the middle the granule hopper. The granules hopper is way oversized, and next time I will make a smaller one. My guess it could take 3 kg plastic. On the right of it the heater and nozzle. On the far right the green thing is the filament puller.

The design is very loosely based on several plans from the web. I could not copy an existing plan, because certain materials are not available very easy here in NZ.


This is the extruder nozzle.

The heater is 60w pipe heater. It was sold as 300w, but that the usual “Chinese” spec!  The 60watt is more then enough to heat the extruder up to 180 degreeC .

At the moment I don’t have thermal insulation, but will add this. I hope the thermal insulation would keep the temperature more stable.

The this green/white wire is the thermo couple temperature sensor. This is placed in drilled hole in a brass ring, so will indicate the temperature of the plastic very well.

The pipe is stainless steel. Most designs use a steel pipe, but could not find it locally. Reports from other people indicated that stainless would not work, but I did not notice any issues with it. Stainless conducts much less heat as steel. This is nice, so the heater does not have to work as hard to keep the head heated.

Below the pipe is some pulverised granules visible. They fall out of 2 small air holes drilled in the pipe. These holes allow air to escape from the compressed granules I don’t know if  they are actually needed, because the air can also escape back to the hopper.

Intern in the nozzle is an fine filter to keep any junk out of the filament. Also is there a breaker plate to helps to build up pressure, and to mix the plastic. It is a metal plate with two 1.5mm holes in them. On the end I extended the nozzle with a pies of brass. This allows the plastic to form a good rounded shape, and also helps to increase the pressure. Before I added it, the extruded filament had a twist in it, This was caused by the rotating screw creating pressure differentials in the head.

The photo was taken with the machine turned off. If the machine is running the extruded filament on the right does not sag. 


Another view of the extruder.

The black fan in the middle cools down the molten filament. By the time it is entering the filament puller (that green thing) the filament is still warm, but hardened.

The fan still needs a bracket. Also some air guides is needed to keep any air flow from the hot extruder nozzle.

The filament puller on the right is pulling the filament in a constant speed. The speed that this runs defines the diameter of the filament. Running it faster creates thinner diameter filament. The nozzle diameter is 5mm. The puller reduces this to 2.6mm or even 1.75 is if run it faster by stretching the still molten plastic.

The design of the filament puller with build instruction can be found here: . While you’re on thingiverse, check my other designs too!


Another view of the puller. Here you can see the rollers that grip the filament. The gray DC geared motor drives the rollers.



The last part of the setup. The filament winder. It uses a friction drive to wind up the filament. The motor runs with a constant speed. A small weight  defines the strength the filament is wound up. It is not very critical. As long as the puller does not the let the filament puller slip it is fine. I don’t have a something that moves the filament during winding. It winds it up quite nice by itself, as long as there is enough distance between the roll and the puller.


Another view of the winder. I was planning to make something nicer with a bearing in the center. But as it stands now it works very will, so no need to change it. It only now needs some wooden blocks to keep the filament spool in the middle.


The filament diameter varies slightly: +/- 0.1mm , and there is every meter or so a small air bubble in the filament. The diameter variations result in a very small amount of waiver in the walls of a 3d prints. The air does not have any noticeable effect.

The end result: nice filament. It is not 100% perfect yet, but still very usable. I have printed 5+ kilo of this filament already! You can see the results all over this blog.

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