I would love to re-use my failed prints by re-extruding the plastic to be used in the 3D printer once again. One thing that stands in my way is finding an effective way to shred the plastic into smaller bits for the extrude to use. What is a good thing to look for to accomplish this? Maybe a really big 'paper' shredder?
there is a project called
precious plastic and there is a plastic shredder, but it is a rather expensive solution.
The paper shredder will be ok as long as you can feed it with plastic.
I'm in the same boat as you, was contemplating spending $2000 on a shredder, and I was inspired by this RepRap article "Plastic Shredder using Kitchen Blender".
In which someone cleverly reminds us that thermoplastics melt. Put them on a baking tray on baking paper:
Melt them in the oven at a high temperature until they're pancakes:
The link puts them in a kitchen blender, but I've had success with a $70 micro-cut paper shredder from a local office supply store. The plastic puddles have a thin edge, which helps them fit into a shredder rated for "5 sheets of A4 at a time" (suggesting 0.3 mm max) but can process about 2 mm thick plastic if it gets a good lead-in.
The micro-cut particles it puts out are smaller than the PLA beads. I do mix recycled and virgin plastic together in varying ratios but mixing them evenly (especially with the dye beads) is tricky - it's very hard to get precise even colouring.
At 1.25 g/cc, 1 kg of PLA in an oven dish ~A4 sized is about 1.4 cm thick. So, aiming for about 100 g of plastic per dish will get you blobs averaging 1.4 mm. That fits through the shredder fine. 10 blobs make 1 kg of filament.
The only issue I have with the cheap office shredder is when you feed something slightly too thick in, occasionally the teeth deform the plastic into a chunk too big to fit into the shredder for a second pass, so that piece needs to go back into the melt queue.