Trash Printer! 3D printing from PP an HDPE flakes!

How to Build the Trash Printer!

Hello all! For 3 years now I’ve been working towards building a 3D printer that prints directly from flakes produced by the Precious Plastic shredder, without the need for making filament first. This spring, I was finally able to print actual objects, and just yesterday I finished and published my documentation for Version 3.1.0 (Versioning convention: Major redesigns . improvements to design .  improvements to documentation)

Polypropylene and HDPE both have relatively high thermal warp characteristics, which make them more difficult to print with, especially for small, detailed parts, compared to PLA and ABS, which is why they aren’t more widely used in 3D printers. However, together PP and HDPE make up over 50% of all plastic waste by volume! Making actual post-consumer plastics into high quality filament that won’t clog a printer, in addition to PP and HDPE being hard to work with to begin with, led me to try and just scale down the basic Precious Plastic extruder design so that it would be about the same size and weight as a CNC router, so it could fit on an existing CNC router gantry and 3D print larger, lower resolution parts without the filament step, reducing cost and complexity.

So far, I’ve printed vases, bowls, cups, geodesic dome connector parts, and brackets for mounting solar panels to the roof of my bus. The printer only takes >200W peak/100W average, and the parts mentioned above took about 30-60 minutes each, so that works out to an energy cost of 50-100wH per part, or roughly the power it takes to fully charge a laptop. The parts are wonderfully light, strong, and flexible. They don’t have nearly the same resolution or detail as typical printed parts (the nozzle is currently 10x the size of a typical desktop printer nozzle) but they are also highly tolerant of impurities, such as food or label bits, and there is still a wide range of useful objects that can made at this resolution, and with a smaller nozzle and a higher-precision gantry, major improvements in resolution are probably possible. I’m particularly excited because there is a whole class of objects this printer can print that could previously only be made by high-pressure industrial injection molding, and can now be made as one-off custom parts a very small scale, at very low cost.

You should be able to mount this extruder to any existing CNC router that is powered by stepper motors, can support the weight of a router, and has at least a few inches of Z travel. I built mine around the mostly-open-source (open but non-commercial) Mostly-Printable CNC (MPCNC), which only cost about $500 to build.

Next steps for me are:
-Making a smaller, more detailed version for printing small detailed parts in PLA
-Making an 2’x8′ long gantry, for printing full honeycombed interlocking beams and trusses that are structurally comparable or superior to lumber and can be easily assembled into tiny homes and other deployable structures.
-Building more heads for different plastics- PLA, LDPE, PET (dried), and ABS.

Making this documentation took a lot of work, and made me appreciate just how much work Dave had to put into make the original set of tutorials and plans so that we could all actually replicate them. So please use it! Replicate! Replicate! Replicate!

I’m a Patron of Dave’s on Patreon, and have my own Patreon, which is If you appreciate this work and have the means to chip in some money, it will help me prototype and improve this system faster, but all of my documentation is freely available to everyone. You can also follow my progress on Instagram – @themagictoolbus

Sam Smith

thanks for the input; I am adding this to the map.
indeed, there is a increasing trend for micro-manufacturing at home; thanks to the DIY community and the industry getting stuff done cheaper(virtually at least); one of my favorite youtubers got a contract with a aircraft manufacturer because contracting larger service providers is getting too expensive as he explains well in one of his videos. I somehow hope that micro-manufacturing is becoming a key corner stone during the transition to the new ara of less labor. making a living from turning waste into products is per se is rather difficult for the most right-now but I think if there were mature and ready-to go sets for relative cheap which can run unattended all day long at low power it could pave the way for km-zero economy;  on the other hand, you can bet on that the establishment will make it very hard as always that somebody starts selling products in the next super market. just look at the tiny fraction who can buy bio or stuff from small internet markets (as bazar) but yet, we’re getting there i think, very late but it’s moving.
sorry for getting off-topic; possibly we build another dossier on the subject; it’s frequently popping up and eventually time to re-consolidate. i know v4 comes with some guidance on business but have my doubts about how close this is to reality; producing X tiles makes X $$ isn’t exactly enough.
And yes, possible products should be part of the machine’s selling features, definitely.

Thank for sharing it, congrats for doing it !
Does your printer require a specific size of flakes or it is not very important?
Do you know if it is important for the other printers which use flakes like 3dseed ?
Thank you

So there’s a few lighter weight direct pellet extruders around, but this looks like a good development. Some of the lighter ones look like their components are a bit weak, and not really up to the task.


A note on printer choice:

You don’t need a CNC router sized machine for this. Some geometries are definitely out of the question. CoreXY & Delta printers really prefer lighter fly weights, and that’s why they’re common for filament 3D printers, because fast acceleration is very desirable and these machines achieve that, by having stationary motors.


However a Mendel style printer can have a fairly robust Z axis. In fact some have been converted with limited success into CNC routers.

I personally have one of these machines in the video above, and have long thought it would be a good candidate for a direct extruder.

The roof of my car ports “aka workshop that keeps wifes car in the rain” is corrugated iron with steel beams underneath holding them on.
I could run a frame on top of the roofing sheets to put the brackets/panels on or I could also add a few more beams under the roofing sheets to get the right distances and then use a bracket on top of the roofing sheet screwed down through it to the beam below.

One reason I love the idea of using plastic brackets (especially recycled plastic) is the fact that with an iron roof and aluminium solar panels any contact between the two would over time cause dissimilar metals corrosion.

I had only been considering the clamp style in the past as that is what I had seen done/offered by commercial installers, I will have to go and have a look at the panels now to see if it could be as simple as bolting straight onto the panel with a plastic spacer to keep it off the roof 🙂

@cartlintech , I’m about to start experimenting with several 100W panels (metal frame). I’m trying to decide whether to use the mount holes on the back of the frames or whether to clamp the frames from the front with HDPE clamps I would molds. For smaller panels (20W) I’ve used both methods.

What are you trying to mount to?

Hi @samsmith, love what you are doing with the flakes to print as well as well basically everything else I seem to hear you are doing like the metabolizer.

I am not here to stroke your ego though today (although everyone does deserve a pat on the back when it is due so I whole heartedly mean the initial comment.

What I am wondering is whether you saved/kept the design for the solar brackets you printed to mount panels onto your bus.
I ask because I currently have around 30 panels sitting around not producing me power yet with no way to mount them and a pile of HDPE staring at me begging to be shredded and put to use, but also about a million other bits of machinery i need to get started on as well.
Even just a picture (although i wouldn’t say no to the actual cad files either) might be enough to tip the balance for me to hurry up and get on with making a 3d printer over some other task 🙂

@samsmith I’m thinking of building one of the MPCNC machines to use as a router and laser engraver. Is yours working well? Any tips for the build?


@samsmith Nice write-up on Hackaday

@samsmith This looks really great.

As you say, being able to print reasonably large items in (contamination tolerant) PP or HDPE, offers many possibilities – even with relatively low resolutions.

And of course the items don’t have to come out of the printer in their finished state. It is possible to treat the printed items as you would a raw metallic sand casting – by subsequently machining precision features (surfaces and holes) to create accurate interfaces.

Hmmm. Time to have a think…

There are more ‘industrial’ 3d-printers around (at least in the Netherlands) than just the vanplastik one (which is actually small scale) and not just limited to plastic like:
- has more listed, Site is Dutch, but most listed sites are not.

So: Extruder + robotarm = Industrial 3d printer (or at least could be).


As on the what to print:
Not going to repeat the whole discussion, I think most of us agree already, so just the highlights: No designers, no products, no sales.
Enable designers to also make a living from recycling plastic and you are golden.
Me? I’m first working on my designs and market before I even start thinking about production.
A 10% commission over a 250% value increase does not seem unfair to me
(for those non-human calculators: that still leaves extra 125% added value for the rest of the production/sales chain) and should be part of the whole ecology.

NOT doing so?: Designers will start their own production lines and keep the entire 150% added value (even adding another 1000%+ when going ‘exclusive’).

And yes: Designs could still be licensed for free or as Open Source, but this is up to the designers to decide (in exchange for e.g. a ‘design by’ line), not for the ‘community’ to demand. You’ll be shrugged away.

That all being said:
No filament printers: Yeah, that’s the way to go!

that’s great news; thanks for sharing; i will add this to the library; i hope i can get a step file out of this for Fusion360

so let me summarize where we are for now, please someone correct me :

1. your printer which can deal with PP and HDPE, no prior extra grinding needed, low detail but strong enough for various applications
2. 3dseed has a printer dealing with PET but needs extra grinding, higher details are possible
3. vanplastik has also a PET printer, enabling larger diameters, ie: funiture
4. i saw within the PP community somebody doing LDPE  filament
5. there are techniques around to make molds from alu foli, plaster,…

that looks good and complete to me. i think now with the PP beams we might be possible to produce small and cheap printers/cncs the Reprap way, from waste. machines produce new machine parts. i like that !

@offtopic : now we’re just short of ideas what to print actually; i kept scratching the last months but couldn’t get somewhere else than : education stuff (mechanics,…), games (license/copyright problems), lego like building blocks to build more machines, incl. a hand shredder for kitchen waste from plastic  and of course design/art stuff but i guess v4 will open up some doors.

thanks again, that’s a good step forward; would be nice to know how the printer has to be designed; i know that a heavy print head like this needs a little more invest; also it’s hard to outperform PET when it comes to printing. i would be happy to know more about.