Recycle Plastic Into 3D Printer Filament at Home

3D printing is very exciting technology as it reaches the home scale but using brand new filament was not acceptable to me as it would just increases the plastic waste amount on the planet. I started to look for a way to turn plastic scraps around me into usable 3D printer filament... On the web I could find many plastic extruders and recyclers but they exceeded my budget so I decided to build my own process. My current system costs less than 100€ with half of the parts taken from scrap.

The process consists in sorting and cleaning plastic pieces taken from defective household appliances, grinding them to small granules, and feed those granules to a home made small extrusion line. After a quick post-processing step, the output filament can be used by a 3D printer to print new objects.

All my work is widely inspired by others projects on the web : Filastruder, Lyman filament extruder, Precious Plastic project and various YouTube or instructables.com contributions. The electronic part is build using Arduino platform. Thanks to all the people behind those projects for sharing their research. Sharing what I’ve learned so far on this topic is my attempt to give back to the community.

At this stage I can produce some 3D printer filament which I was able to print some things with. RC drone frames, chair plastic feet, gears and parts of the extrusion line, battery holder for e-bike and others stuffs have been successfully printed with that recycled filament. That said, I’m not fully satisfied with the process as the filament output is no yet super accurate and also because the grinding system I use is not able to grind some medium and small pieces, that are left over for now.

I started working on this project 3 years ago (Jan. 2019), and what I expected to be a 2 months project ended being a never ending story of try-fail-think-improve-try-again-break-rethink-and retry… almost a half-time job, but with many holidays ; ) . I’m glad to share what I’ve learned so far and hope you’ll find some useful things here.

As I have hard time fitting the whole process into a single Instructable format (many steps and sub-steps), I provide a complete guide as PDF that you can download and use offline. In this Instructable I will summary the mains steps that you'll find with more details inside the PDF guide. Going through that Instructable will give you a good idea of how I proceed, and you'll got more and bigger pictures here than inside the pdf guide.

So. If as me, you wish to recycle plastic scrap into 3D printing filament here is what I can provide you to get inspired and build your own system :

• A detailed PDF guide about how I do it.
• All the 3D models used to build the extrusion line. (hosted on thingiverse )
• The source code of Arduino's program driving the extrusion line.

Below, you can download the PDF guide and Arduino source code files. Have a look at the thingiverse link for 3D models. If you feel like, have a look further to get an idea about what is inside the guide.

Looking for recycling plastic obviously means you’ll need some plastic to recycle… I find mine from old household appliances given by people around me. I take also some out of shops waste bins where the waste are not going to be recycled.

Once you’ve got the material, be sure to sort your plastic by type as they don’t react the same to heat and don’t always mix in a good way.

The dirt can clog your extrusion line or pollute your filament, it can also clog your 3D printer nozzle. I wash the part with water or using a cloth.

Here is my set up for grinding : an electric hand plane fixed on an heavy wrench. This system is inspired by joshmt2012's instructable : https://www.instructables.com/Low-Cost-Plastic-Shredder/

The cardboard box is here to keep plastic projections from flying everywhere. I use a small tube to hold the planer switch ON.

The vacuum cleaner bag is meant to catch the ground output which consist in some plastic shavings and granules. The main output should go to the bag, but around 25 % ends around the plane.

You'll find more details inside the pdf guide but the main word here is caution for your fingers !! The electric hand plane can catch and bite your hand quicker than you could react !!

For that reason I use pliers to hold pieces when the distance between the blade and my hand is under 20cm.

Some plastic (ABS for instance) needs to be very carefully dried before to be extruded.

Over time, moisture get inside the structure of the material and stay trapped in here. When the material is heated again, vapor will expand the plastic like a bread dough, causing bubbles inside the filament. I had success letting the plastic shavings inside an oven for 60min at around 90°, checking the temp with an infrared thermometer. During drying, I left the oven’s door opened. I like to do the drying step when the plastic is still airy. I mean, I think the moisture is more prone to get out of airy plastic shavings than compact small granules or powder. Also shavings will less likely stick together than granules or powder.

I found better to fine grinding the plastic shavings to get as homogeneous as possible the material fed to the extrusion line. I use an old coffee grinder for that step and a homemade sieve to check the grinding.

At that step you go ready to extrude material... but well, we need an extrusion line !

Here is my attempt at making a cheap extrusion line that would be able to extrude plastic granules and shavings into usable 3D printer filament. All the part should be easy to source either on the web, at your local hardware store or even scrapyard. It features :

• Old ATX power supply : 5V and 12V used.
• Salvaged hand drill powertrain with bicycle wheel hub and 3D printed gearing.
• Security switch (to avoid breaking stuffs !).
• Old style plumbing pipes extruder with wood drill as extruding screw from Aliexpress or local hardware store.
• Hacked 12V boiler as barrel heater.
• Mostly 3D printed puller module.
• Output flow rate sensor module.
• Arduino interface and program for temperature and filament diameter regulation.

I hope you can get inspired by the pictures to build your own cheap Arduino controlled extrusion line. Check the pdf guide for much more detail about the building process and supplies (This part could fit in one full Instructable).

By the way you could have a look at the projects linked below. Those are the main projects that inspired my build process :

• 3D filament factory by instructables user ianmcmill : https://www.instructables.com/Build-your-own-3d-printing-filament-factory-Filame/
• Lyman/Mulier filament extruder : https://www.thingiverse.com/thing:380987
• Filastruder : https://www.filastruder.com/
• Diameter sensor by thingiverse user ilornate : https://www.thingiverse.com/thing:636420

Once built the cheap extrusion line and having some granule to extrude, it's time to start tweaking the settings to get the most accurate filament produced.

The ground plastic fed to the extrusion line is not as homogeneous as industrial pellets so it can go through the barrel more or less quickly. I mean, for one single rotation of the extrusion screw, the amount of extruded material will differ with another single rotation. While the puller module is pulling at constant speed, the amount of extruded material varies over time, causing filament diameter to vary accordingly.

The extrusion screw is driven by a geared motor (pusher module). By changing the pusher module’s speed according to the measured diameter of the plastic output we can try to keep the flow rate as constant as possible.

I heavily recommend you to read the corresponding chapter of the guide for more details (as this step could be an Instructable itself also), but basically the extruding steps are :

• Preheat the extruder
• Start the extrusion screw
• Feed the hopper with plastic granules
• Start the puller module
• Place the outgoing plastic filament between the puller's cylinders
• Tweak some settings to get a good extruding base for the automation
• Rise P, I, and D gain a bit and activate PID mode
• Tweak P, I, D and Measured output diameter target until you get the more stable production
• And finally save those settings inside Arduino's memory for the next time !

The video above shows the extrusion line working with the PID regulated mode activated. We can ear the driving motor changing it's speed according to the measured diameter of the melted plastic flowing at the extruder's nozzle.

Finally we got some filament ! but wait a minute, for now the production needs to be checked and sometime post-processed in order to be printable.

Our small extrusion line produces a filament which is sometimes too thin, sometimes too thick comparing to what accurate commercial grade filament is. That’s OK if you don’t print pieces with too much details, but sometimes the produced filament is even not accurate enough to be used by the 3D printer. It could be such thin that the extruder gear couldn't grab on it or such thick that it would just get stuck somewhere in the bowden tube or cold zone of the print head.

On my side, I try to remove all filament that’s less than 1.5 mm diameter. To refine too thick filament, I use that home made tool and cutter blade.

Once you’ve got your ready-to-print filament it’s time to experiment with some print jobs. I used all my filament sample made for documenting the project on tuning prints parameters to achieve an almost acceptable printed part. This was my first attempt at printing recycled ABS.

The last black part have still some under-extrusion or layer bonding imperfections. As I had no more black filament left, I made another test print with another ABS recycled sample produced by myself too. Setting up a thinner filament diameter in the slicer was the key to obtain a nice layer bonding.

Still reading around ? Thanks for the interest !

I hope that yo got inspired by my process. Of course there is still a huge potential for improvement with filament accuracy and recycling efficiency, and also with improving printing of some not-so-easy-to-print materials (recycled PP for instance). Anyway, with an already usable 3D printer filament as output, I see that process as a starting point for recycling plastic locally and at a very small scale.

If you feel like diving into that kind of activity have a look at the pdf guide provided (well, ok, it looks a bit like an advertisement... but it is free !). Of course every questions or comments are welcome and I would be really pleased to share some thoughts around the topic !