How does local recycling work | Part 2



Welcome back! In this series I will explore the potential of recycling household plastic waste into homemade 3D printing filament.

In the first post I looked into the different reasons for making your own recycled filament. So now that you’re all fired up to start cranking up production, let’s look at how to get things moving .

The process of local recycling consists of 4 main steps:

  • Collecting and cleaning
  • Shredding
  • Extruding
  • Printing

(Source: Better Future Factory, design by Studio Dolour)

The objective is to produce filament that will flow easily through your printer. Therefore it is important that the diameter and weight of the filament is consistent throughout the filament. Diameter inconsistency can cause different problems when printing:

  • When it’s too thick it won’t fit through the feed tube/extruder head
  • When it’s too thin it won’t be properly pushed forward because the gears can’t grip it.
  • When it’s too thick too much filament will be used when printing causing blobs in your print
  • When it’s too thin not enough filament will be used when printing which can create weak spots or even holes in your print

Weight consistency is important because it can reflect the consistency of the diameter of the filament and in this way serves as an indirect quality indicator. It can also point directly at the issue of different types of materials mixed in the filament. This can cause all sorts of troubles when printing because of the different material characteristics. If one material has a higher melting point for instance it might not melt properly causing lumps in the filament that can end up in the print or even worse can plug up your printer.

But not to worry, I have done some research and will provide full insight into which elements to control soon. For now it is good to mention that the diameter of the filament is by far the most important parameter. The way to keep this as constant as possible is by ensuring that the pull on the filament when extruding it is constant.

So what does the process look like?

Our friends from the Better Future Factory have made a great video that shows all steps of the recycling process:

Step 1: Collecting material
It is very important to use a single type of material (plastic) for making new filament. Thus make sure to separate your waste before hand. The 2 most commonly used plastics for 3D printing, ABS and PLA, have very different characteristics, melting point for example, which if combined can cause serious problems later on in the proces.

Two different pieces of ABS might also not be the same. First, from a chemical perspective there are many different polymer types that are gathered under the name ABS. Second, the way the material was processed the first time around can influence the way it behaves when recycled. Especially the print temperature of the first round is expected to play a role since a higher temperature means more polymer chains have been broken down which results in a weaker material. However other aspects such as the infill percentage and layer height might also play a role. So when recycling old prints in general it is a good strategy to use old prints that are as similar as possible.

Other things to watch are that the material is dry, clean and not too old. Dry because water (especially in PLA) can cause problems when it is heated and the water starts to cook. This can cause bubbles to form in the material which causes the filament/print to be porous. Clean, because dirt etc. can cause plugging of the printer or can end up in the filament/print your producing. Caution should be taken with old prints because ABS and PLA react with air and degrade as a result of this. Especially for PLA this can have a pretty big influence.

This all holds for recycling your old prints but it works just the same for new ABS or PLA pellets that can also be used to make filament. So, when buying new pellets at least make sure to look for pellets that are 100% pure ABS or PLA. Also a supplier of pellets specifically made for the purpose of using it for 3D printing such as Colorfabb might give better results than ‘normal’ pellets.

Step 2: Shredding
The next step is to shred the material into smaller pieces. This is done first of all to be able to fit the parts into your shredder. Also the more equally sized the pieces are that you feed into your extruder the more consistent the filament that comes out will be. Basically shredding can be done in whatever way you like as long as the material is made into sufficiently small pieces. I myself use the Filamaker, a shredder produced by Marcus Senicky.

shredder op tafeltje cropped.jpg

How small the pieces should be depends on your extruder but our guess is that smaller is better. At this point, I expect that more homogeneous parts will probably extrude better. So, also for shredding, I try to keep “consistency” as a general rule.

Step 3: Extruding
In this step the filament is actually made. This is done using a machine that is called an extruder. At this moment there are several extruders available that are easy to use at home and with Kickstarter projects popping up regularly it is expected this will only increase. My next post will go into detail on this but for now let’s look quickly at the way these machines work. The basics are the same for all extruders and come down to this. The shredded material or the pellets are fed into a ‘hopper’ which is basically the mouth of the machine. Then they fall into a screw that spins them forward and passes the material past heating elements which melt the plastic. After the plastic is sufficiently melted it is pressed through a nozzle that, if all goes well, presses it out into a perfect string of filament. The next series of posts will be all about how to do this and what results I was able to get. To get the picture check out the first part if this youtube video:

Step 4: Printing
The last step which of course is the main goal of it all is to use your material to actually print some awesome stuff. In a later series of posts I will look more into how that can best be done and if there are differences compared to ‘normal’ 3D Printing.

So that’s an overview of the steps to take to turn your old print into a new one. In my next post I will give an overview of the shredders and extruders that you can use to make this happen!


Hi Bram,

Keeping up the good work with these posts, I see! I would like you to clarify or elaborate on this statement from Step 1: Collecting Material.

“However other aspects such as the infill percentage and layer height might also play a role.”

What sort of role, and how was this determined? I am really curious about the details of your findings, and can’t wait for Part 3.




Thanks a lot! Good question, at this point it is an assumption I’m making based on my experience with extruding with the Filabot. For instance if you print in low infill percentage this can cause your print to become a bit like flakes when shredding it. My experience is that these flakes sometimes can be more difficult to process for the extruder which can cause the filament that you produce to be less consistent.

For small layer heights there will be many layers in a print and relatively speaking a lot of binding between the layers in a small piece of material. This could cause the filament that you extrude to be less homogenuous. This is really just a guess though.

So these are merely assumptions and I haven’t tested these so please don’t take it as the truth it is an idea of something that might be the case to underpin my assumption that more homogenuous material as input produces more consistent filament. This assumption hasn’t been tested but I will do some experiments soon to see to what degree this holds.

Let me know if you have any other questions!



Very good post, i was thinking ahead for the future to start a process like this aswell, this will help me alot in the future, keep it coming!


Very good post, i was thinking ahead for the future to start a process like this aswell, this will help me alot in the future, keep it coming!


Thanks will do :wink:


Hi again,

Thanks for the in-depth reply! This kind of detailed thought-process is exactly what I was hoping to encounter in your recycling post series. Not having actually used any of these devices myself (yet!), I’m sure there are aspects of the process that I am imagining/visualizing inaccurately.

Reading your post gives me a pretty good sense of what you mean, and has changed how I think of the plastic’s transformation as it gets passed along the screw. I had assumed that the plastic was melted and mixed thoroughly enough that features of the print would be completely obliterated. It sounds though, that this might not be the case.

Which leads me to wonder, should we (the 3D printing community) be developing one more device in the plastic life-cycle? Between grinder and extruder, should there be a melter/mixer/granulator? Hmm… Who knew, getting into 3D printing, that you’d soon be jealously eyeing dusty and expensive tomes? I sure didn’t! Guess I need to go back and see what industry does - no need to (completely) reinvent the wheel!

Thanks for sharing your research and knowledge!




Thanks for your kind comment, very nice to hear that you like my posts!

Thanks also for further thinking about the whole process, interesting to hear. However I think you’re going a little fast. My impression is that the plastics definitely is mixed and melted properly enough to obliterate the features of the print when passing through the screw. However it might be the case that still even well mixed materials perform different than homogenuous materials. I don’t know if this assumption holds so this is something that further research will hopefully point out.

My experience is that when using materials that are properly shredded so that they have pieces of roughly the same size and shape this is easier to feed into the extruder which causes a more constant output of filament. However this is more a matter of making sure you shred the material properly and in general the Filabot extruder screw is rather tolerant I would say.

So for now I would say that an extra machine in the middle of the process is most probably not necessary but let’s see how the rest of my experiments with printing and extruding with different materials go!





Thanks again for sharing your thoughts!

I suppose that I have one final clarifying question regarding this statement, “However it might be the case that still even well mixed materials perform different than homogenuous materials.”

I have been assuming that you are recycling prints of the same material together, but this may be incorrect. What are you considering ‘well mixed materials’ to be versus ‘homogeneous’ materials? Are you writing about homogeneity in shape and size of the crunched up bits, or of the actual thermoplastic material composition?’





Thanks again for sharing your question. In my further research I will look at mixing of two different types of the same material. Specifically shredded old prints (produced with the same shape, settings and filament) and new pellets. So I consider each when extruded separately to be homogenuous.

- The new pellets are homogenuous in: shape, size and thermoplastic composition.

- The shredded old prints are homogenuous in thermoplastic composition but not in shape and size. Because the size after shredding is sufficiently small to be adequately extruded by the Filabot even if the pieces aren’t equal I still consider this to be homogenuous.

I consider a mix of these two to be a well mixed material. Keep in mind that I’m only mixing with materials that are the same, so either all PLA or all ABS since mixing these two generally seems like a bad idea regardless of the situation.

Please let me know if you have any other questions!


Hi Bram,

Thanks for putting together this series about recycling plastics;

Would you be able to expand upon the cleaning stage, as PLA comes in many colours?

How does one remove the pigment in print as PLA is natural in colour?




Thanks for your comment. I haven’t come across any info on how this can be done so far but when I do I’ll be sure to share. @Bhavya_Jain do you perhaps have any knowledge on how this can be done?