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Plastic Recycling

The lab has a system for shredding and recycling 3D printing filaments. We're currently set up to process PLA and PETG.

Note: The product is not very user friendly or complete. The documentation/menu options/firmware code descriptions are not always complete or in proper English as it is not the author's native language. The firmware could be improved a lot.

Sorting & Storage

Put your unwanted PLA and PETG prints in the labelled Really Useful Boxes under the workbench in G11. Some geometries are easier to shred than others, so consider the following when deciding what to put in the recycling and what to throw away:

  • The optimal object for shredding is something with an uneven shape in all three dimensions and <40% infill. The further you get from that, the harder it will be to process.
  • Cut up bigger stuff so it fits into the recycling box (10x10x15cm), otherwise throw it away.
  • A good tip for anything that is big and flat that the shredder teeth will struggle to grab is to lean the shredder about 30 degrees to the right so they slide into the teeth better
  • Don't try to recycle anything flexible, like unprocessed filament or a failed first layer that came off the printer as a flimsy plastic sheet. Works fine

If you want to recycle something but the box is full, either do some shredding or toss it in the bin - don't overwhelm the lab with unprocessed recycling.

When you are shedding a new material, vacuum out the blades, hopper and collection drawer the materials don't mix.


The shredder is pretty simple to operate. Make sure it's plugged in and the drawer that holds the shredded bits is empty (don't worry about the tiny bits clinging statically to the inner surface 1) ). Load a few objects into the hopper at the top, close the lid, flip the switch by the power cable, and press the button on the top.

You should hear the motor struggling occasionally and running backwards to clear jams. If you hear the steady sound of a motor unbothered by anything difficult in its path, stuff is probably not actually reaching the shredder teeth. Press the button to turn the shredder off (DON'T rely on the safety switch under the lid, it's software controlled) and re-seat a few things.

Empty the drawer from the bottom of the shredder into the bin labelled “shredded”. There is an oval sieve I printed to filter out the bigger bits and feed them back into the shredder. Smaller pellets are easier to extrude. You can run them through the shredder 2-3 times to make it easier later.

You can fill the hopper and leave it running, it will automatically turn off after a while of it detecting there is nothing to shred.

Shredding plastic bottles

You can shred plastic bottles and other products after you have washed them with soap and warm water and dried them. Leave a note on the container for others to know what settings to use. The shreddings can be used to melt into a sheet, then laser cut to make things like boxes. Steph also has a small injection moulder in his office. Costa might be interested in an injection moulding project too.

Extruding and Spooling

Optimal settings for this process are still being worked out, and there may be some adjustments to the firmware and controls on the extruder and spooler. In the meantime, if you want to try making some filament, check out the manuals on the Felfil website and proceed at your own risk.

Values given by Felfil:

Material Temperature (*C) Mode Screw
Current (A)
PLA 185-220
depending on formulation
Soft/Hard 7 0.7 yes
PETG 210 Medium 7 0.7 yes
ABS 210 Soft/Hard 9 0.6 yes Safety 2)
Nylon 240 Hard 9 0.7 yes
HDPE 200 _ 9 0.6 no
HIPS 200 Soft 9 0.7 no
TPU _ Medium _ _ _ 2.85mm extrusion only
PP _ _ _ _ _
PET from bottles up to 270? _ _ _ _

(The documentation is conflicted about if PLA should be ran with soft or hard mode, both seem to work. Update the wiki with settings you find work better)

Add raw pellets 40-60% by weight. 100% recycled is also possible, but worse quality, not yet tested in the lab. Coloured filament: add 2% pigment by weight

Run the filament through a spare 3d printer heatbreak to check all of it is not over 1.75mm, which will cause an annoying jam mid-print

Mode controls the PID constants used to control the filament width.

“Custom” allows you to set the winding speed manually. The control isn't fine enough and would need to be tweaked in firmware to be useful.

The extruder can work for a maximum of 4 hours at a time, cool it down for 2 hours before turning it on again.



To do:

  • Figure out how to get the encoders on the extruder and spooler working better.
    • Tweak the firmware to make all the menu options easier to adjust (make it have finer control and quicker to get to desired value)
  • Add another fan to the extruder to cool the motor directly.
  • Intermittent firmware bug with filament sensor - it detects the width correctly (verified with Serial.print in firmware) but does not start the motor. Sometimes it works, sometimes doesn't.


  • Printed a bigger hopper
  • Changed the pitch of the distribution winding mechanism as it was taking frustratingly long to move it from side to side. (In firmware, find and replace all instances of '79' with '19' to update the distance it now has to travel
  • Changed the filament sensor a little to make it easier to insert material
  • Soldered in a barrel jack that doesn't randomly disconnect



  • Filament shredder set up


  • Filament shredder making terrible screeching noise when it reverses
  • One of the fins is bent
  • Replacement part to arrive from Felfil


  • Original fins fixed. Disassembled and bent back into shape with some precise taps from a hammer
Todo: buy an alpha ray source to dissipate static charge
The styrene fumes it gives off when melting are very smelly and can give you a headache, use extraction. Do your research and follow the safety recommendations
plasticrecycling.txt · Last modified: 2022-06-01 00:17 by MirZa

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