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MAKE subscriber Rob Torcellini of Eastford, CT, sent in his extrusion system for turning HDPE pellets into thin, textured strips his plants liked.

I built a plastic extrusion system to make synthetic growing media for my aquaponics system. It uses the Teensy AVR microprocessor from PJRC, an old windshield wiper motor and a few Legos!

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal



  1. Jrod says:

    That extruder looks really good! I like the temperature control. You mentioned that you were hoping for bacterial growth with the polyethylene so I understand the waffle pattern, but I’m curious as to why you chose to use HDPE as opposed to polystyrene. Polystyrene is susceptible to UV damage, but it has great surface energy and will inherently harbor microbes. It also has a processing temperature around 250 to 300 degrees F, but you’ll end up with degraded stagnation around the inside of the die if it stays that hot for too long. You can get grades that have UV resistant additives and such. Is there a reason for sticking with HDPE that I didn’t see? It looks like you may have just been experimenting with whether or not it would work but I thought I’d ask.

  2. Spades says:

    As soon as I saw the picture I was reminded of strapping that is used for packagings. Might have worked just as well without the need to manufacture a new kind of material and the corresponding machinery.

  3. Rahere says:

    As someone on his main blog pointed out, cut out the rollers and reprap becomes environmentally friendly, recycling milk bottles and the like.

  4. kuekenstall says:

    My compliment for that extruder, the experiment has succeeded really very well. But why do you use HDEP instead of the polyethylene? Every chemist knows, that the polyethylene has a very big surface energy. But maybe you have made in this area a new discovery? This would interest me really very much.

  5. Iceman086 says:

    Could it be possible to use plastics from soda bottles or even old milk jugs to run through the extruder to create an extrudeable cord? Something that could be fed into the Makerbot? It would reduce the material cost of the Makerbot and provide a material that is a bit tougher than ABS plastic.

    All that you would really have to do is change the die head and draw the line out further to allow for cooling and spooling the cord.

    1. Jrod says:

      Recycling would depend on the material. I may not speak for the designer of this machine, but from my experiences, soda bottles don’t recycle as easily as milk jugs or other consumer plastics. To make something to feed into the Makerbot you might want to consider gathering up polypropylene or polyethylene (HDPE, LDPE, LLDPE etc) but avoid PET since it poses potential hazards during degradation if it sits at processing temperature long enough. Both PP and PE are also olefins, which means that they have very low surface energy and will be harder to paint or glue if there are any secondary operations planned for Makerbot parts. If that’s not an issue for you, it’s certainly worth investigating!

      1. Iceman086 says:

        So if I am reading this right…

        Things with a #2, 4 and PE in the center of the recycling symbol are all viable options for reuse? I realized after posting that soda bottles would be a bad choice due to their being hazardous when melted. But the rest could easily be found with a little effort (and a bit of washing) on a recycling day in most neighborhoods.

        The PP and PE would be ok even if they aren’t paintable because they could be used in rapid prototyping things that need to be moulded and casted in a different material.

  6. Rik says:

    I would like to try some in my filters for my aquaponic systems. It looks interesting and should work better than a lot of the materials on the market today. Do you have a blog about your aquaponics systems?



  7. Brian Stott says:

    Hi, Very ingenious. Have you ever seen the 3D printing movement? Start with MakerBot’s Thing-O-Matic. Your device would be a great item to submit to Thingiverse – If you are not familiar this site was setup to submit great projects for admiration, duplication, improvement, discussion and fun. I found your item by searching for people recycling plastics. I’ve just begun playing in this called, ‘hacker’ area and was thinking about the process to make filament for our 3D printers.