The Precious Plastic project has a number of CAD designs as part of their starter kit.
Included in their starter kit is a design for a plastic material shredder.
The Aluminum Recycling Micro Factory project will be borrowing a number of the design choices from there with a couple of exceptions.
The first is that the first motor to be tested will be the nearly ubiquitous windshield wiper motor. It runs on 12 VDC and has enough torque to hopefully shred popcans.
Since we're going a bit smaller scale than the plastic shredder used by Precious Plastic, the blades will be smaller but the overall design will still utilize plasma cut mild steel.
The first iteration of this backyard recycler design will also use threaded steel rod instead too.