Trash Printer - Recycled Plastic 3D Print Head

This is a design for a low-cost extruder for printing objects directly from recycled plastic flakes, instead of using filament.

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In the fall of 2016, I built a 'Precious Plastic' open source plastic shredder, and started experimenting with what I could make with shredded waste plastic. I built the Precious Plastic extruder, but was frustrated at how difficult and time consuming it was to create anything actually functional or useful.

So I began to modify the Precious Plastic design, putting it on a vertical axis and trying to make it light enough to fit on a CNC router gantry, and power it with a stepper motor so that it could be controlled using existing 3D printing software. After many iterations, I finally got it printing this Spring, and the results have been very promising!

It can currently print low-resolution objects with a build area of 24" x 12" x 4", but those dimensions are limitations of my gantry, not the extruder itself. It is printing with Polypropylene (#5) and HDPE (#2), which make up over 50% of the plastic waste stream by volume. Here's how to build your own

This project is intended to be easy to replicate using widely available and easy-to-fabricate parts. It was inspired by the Precious Plastic movement, independently developed by Sam Smith, with a lot of help from a lot of people, especially Darcy Neal, Molly Miner, Nathaniel Garst, and Emma Pritchard.

You may freely share, modify, replicate, remix, re-document, and improve this design, freely and without permission. This information is licensed CC-BY-SA, Creative Commons, Attribution, Share Alike. I ask for attribution because its nice to get credit for open work, and it lets me know who is replicating this work, which is how I judge the success of my documentation. I ask that you share alike so that this information remains free and is able to be rapidly replicated and improved by people around the world. You may use this information for commercial purposes, but you MAY NOT sell or restrict access to this information for commercial purposes.

This print head is simple but effective, and stands to be improved significantly. If you have skills and time to make mods and improvements, please do, and please share your work with the same level of detail that I have. If you appreciate this work, which is completely free and available to everyone at no cost, please consider supporting me on Patreon so that I can keep doing this.

The purpose of this design is to enable printing of large, strong, flexible objects directly from recycled plastic flakes made from common recyclable plastics (currently PP and HDPE), without the need to make recycled plastic into filament. It is not intended to have the same resolution or rigidity of desktop printers, although with some improvement to the extruder, software, and gantry, much higher print quality is probably possible.

You should be able to mount this extruder to any CNC gantry that can support a router, runs G-code and has at least a few inches of Z travel. I am using an "MPCNC" gantry, which costs under $500 in parts and is mostly 3D printable. You can find plans for that at

You will have to dial your extruder to your gantry and preferred software, I am using Repetier Host software, Marlin Firmware, running on a RAMBO 1.4 board at 24VDC. I am using an Solid State Relay (SSR) so that the 24DC from the control board switches 120VAC on and off to the band heater. The band heater is what allows for high-throughput, and I have "tricked" the software to control its temperature by telling it that it is the "heated bed".

Polypropylene and Polyethylene are both highly self-adhesive, which means excellent layer adhesion, but poor bed adhesion. I have solved this problem simply by printing directly onto Polypropylene sheets, eliminating the need for a large heated bed in order to get good adhesion. At the right temperature, the extruded PP will adhere but not fuse to the base-PP, and the parts simply pop off once the print is finished.

I am running the barrel heater (treated as bed heater in software) at 220C, and the hot end at 245C. I am not currently using a part fan, and I believe that if I did it would improve print quality, especially on smaller parts where layers have less time to cool.

Feel free to leave questions in the comments, and I will try to answer them as best I can, and please let me know if you replicate this design, as that is the ultimate test of any open hardware.

This project is a sub-project of my larger "Metabolizer" project, which was a finalist for the Hackaday Prize last year.

Print Head V3-1-0 MPCNC Mountign Bracket.stl

Attaches to the MPCNC gantry (1" OD model) to allow easy mounting of the print head.

Standard Tesselated Geometry - 71.18 kB - 06/13/2019 at 17:26


Print Head V3-1-0 MPCNC Mounting Plate.stl

Attaches to the top of the print head to hold it to the MPCNC mounting bracket.

Standard Tesselated Geometry - 54.77 kB - 06/13/2019 at 17:26


Print Head V3-1-0 Bottom Assembly 4.stl

Bottom assembly creates a funnel for the flakes, holds the pipe flange in place, and acts as a heat brake to reduce thermal creep. Wooden parts are recommended.

Standard Tesselated Geometry - 55.55 kB - 06/13/2019 at 17:26


Print Head V3-1-0 Bottom Assembly 1.stl

Bottom assembly creates a funnel for the flakes, holds the pipe flange in place, and acts as a heat brake to reduce thermal creep. Wooden parts are recommended.

Standard Tesselated Geometry - 52.04 kB - 06/13/2019 at 17:26


Print Head V3-1-0 Shaft Coupler Adapter.stl

This is a fairly hacky and experimental part that couples a typical "plum" style shaft coupler to a roughly 8.5mm hex shaft, the size that most wood augers have in the USA. The stepper shaft is 12mm, but I couldn't find a corresponding coupler for the auger side, so I just cut this part in 1/4" plywood, and it works just fine.

Standard Tesselated Geometry - 25.67 kB - 06/13/2019 at 17:26


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  • 1
    This is an animation of the scenes of the SKP tutorial

    More documentation to come, but if you stop and start this video, you'll get a good idea of how the parts go together. 

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M K wrote 07/05/2019 at 23:31 point

Amazing progress Sam! I'm so stoked to see you in a hackaday email.  Wow!  The documentation in your video looks stellar. The gantry and new hot end look great. I love it! Kudos and good luck. 

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IT-Wizard wrote 06/24/2019 at 08:06 point

This kind of pioneer we need. Hat off mister.

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jqball2u wrote 06/19/2019 at 23:47 point

This is TOTALLY  *awesome*!!!

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Drew Pilcher wrote 06/19/2019 at 22:14 point

Awesome Idea! Whats the reasoning for the large diameter extruder nozzle? What would happen if you tried to use a regular extruder?

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Mateus Silva wrote 06/19/2019 at 23:37 point

If I had to guess, the wood auger bit acting as screw conveyor doesn't exert enough force to push the plastic through a regular extruder.

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Sam Smith wrote 06/20/2019 at 02:07 point

My new nozzle on my Version 3 extruder is 1/8" instead of 1/4", and we'll see where that gets me. I don't actually know what a regular 3D printer nozzle would do, but at this point the gantry I'm using isn't even tuned enough for that kind of resolution, so I'm not going to try it just yet. Check out the RichRap project if your looking for desktop-3D printer resolution from plastic flakes. The lower resolution allows for a lot of lee-way in the quality and consistency of the material, which is important if you want to use truly post-consumer plastic. HDPE and PP are extremely common and widely available, but they have high thermal warp issues and are often dirty, and so printing with a larger nozzle gives you a bit of wiggle room on both of those issues. That said, slightly higher resolution would be great, and I don't know where that lower limit is yet, but I'm trying to find out. I'll post when I've got the 1/8" nozzle printing with HDPE and hopefully that helps a little.

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