Build a Bike-Powered Plastic Shredder (Based on the Precious Plastics Shredder)

I modified a bike to power a plastic shredder, built on the Precious Plastics 3.3 shredder design and iterated for real-world use. This build is safer and more stable than previous versions, tested in a classroom setting, and fully documented with CAD files, a complete BOM, and a step-by-step build video. If you want to shred plastic without electricity, this is the build. It's not meant to be a "perfect" machine, but it does a fine job. Great exercise too.

This project builds upon a previous precious plastic project here, and makes the frame a whole lot safer and more stable, especially for use around kids & high school students: https://community.preciousplastic.com/library/build-a-bicycle-powered-shredder

Step 1 is a build video of the process, and Step 2 includes all the files for CAD/assembly & the BOM.

Standard hand tools: drill press or hand drill, allen keys, basic workshop tools. Some parts require outside fabrication, either through a local shop or online contractor: 3D printer, laser cutter, waterjet, CNC, or plasma cutter.

Full BOM with specs and materials sourcing notes: https://drive.google.com/drive/folders/1sLNrfrv-DeH-Gd9XqJ6TolQJ2PJYwZQX?usp=sharing

The video walks through the full assembly process, key design decisions, what we modified from the base PP 3.3 design, and what we learned through iteration. Watch this before you order anything. It'll save you time and give you a clear picture of what you're building before you commit to parts.

Download the full STEP files and complete BOM with specs and sourcing notes, then order your parts before starting the build. While I designed the bike shredder Autodesk's Fusion 360, the STEP file works in any FreeCAD, SolidWorks, or other CAD software.

https://drive.google.com/drive/folders/1sLNrfrv-DeH-Gd9XqJ6TolQJ2PJYwZQX?usp=sharing

You'll need a standard second-hand bike before continuing. Repair shops, local marketplaces, and charity shops are all good sources. Any bike with a working rear wheel and drivetrain will work.

The base is the standard Precious Plastics 3.3 shredder box. Build it from the official PP plans or buy one from the Precious Plastics Bazar. No modifications to the box itself are needed, so any correctly built 3.3 box works as the starting point.

The frame holds the shredder at working height and gives the bike a fixed mount point. You need enough clearance below the shredder output for a collection bin, and the bike needs to sit level for correct chain alignment.

The build uses a custom steel flywheel and driveshaft to transfer power from the rear wheel to the shredder input shaft. Get these plasma cut, waterjet, laser cut, or CNC'd at a local fab shop. Alternatively, stack 2mm steel plates or use a single 8mm sheet. Both approaches work.

The rear wheel drives the shredder via the bike chain, routed through the steel flywheel to the shredder input shaft. The bike mounts to the rear of the frame with the rear axle fixed in place. Chain tension is the fiddliest part of the whole build. A derailleur tensioner may help, though the extrusion should be sufficient for changing lengths as needed for minor changes.

Run a few test pieces before committing to a full session. Check chain tension under load. Once it's dialed in, it runs consistently. The build video shows normal operation so you know what to expect before you start troubleshooting.