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

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.”


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