Plastic Shredder Research

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Tobben's notes from 2 Nov 2016

Web search shows that many have built their own DIY plastic shredders. Most reach good enough performance for small scale plastic recycling.

Most designs utilize rotating cylinders (sometimes called rotors or shafts) with 2-6 teeth per rotation. The teeth are commonly mounted along a "wave shaped" path on the cylinder perimeter.

Things that differentiate common designs are:

  1. Rotor Construction and Structure
    1. Layers of sheets with teeth, small machine example:
    2. Solid cylinder, complex tooth shapes, bigger machines examples: and
  2. Number of Rotors
    1. Two-rotor Shredder example:

Very simplified, one can say that some shredders "grip" and "tear apart" their material while others function more like a coarse file. Most DYI designs use "grip and tear". Their rotors are either:

  1. Two rotors built from layers
    1. Open Source examples: Mini Shredder and Jason Knights Shredder
  2. One rotor built from layers
    1. Open Source example: Precious Plastics shredder

These are suited to shred thin plastic like bottles, cups and thin 3D prints. Potential problems with "grip and tear" (often realized with two-rotor-designs and large hook shaped teeth):

  • Safety. Hooks might grip and chew on fingers.
  • Grips only relatively flat or edged objects. Won't shred to big and/or round objects.
  • Shred output size is rather random. Re-shredding is sometimes necessary.

Single-rotor shredders with "grinding" teeth work better on more massive and/or round objects. Proprietary example: WEIMA plastic shredder Spider 1500. Potential benefits of single-rotor shredders:

Potential benefits of "grinding" compared to "grip-and-tearing":

  • Predictable shred size. Less need for re-shredding.

Conclusions from 2 Nov 2016

For recycling of smaller 3D prints, both the Precious Plastic Shredder and the Mini Shredder seems good enough. Precious Plastic seems to have the most active community. I therefore advice Opena to join the Precious Plastic (Shredder) community while working on a 3D print recycling workshop. Should the need emerge to shred larger 3D prints, I recommend designing a single-rotor shredder with small square teeth (as opposed to large gripping teeth. Example: