The machine

I use an LXXT-180 shredder from Alibaba. When ordering, I asked the manufacturer to install a 4mm metal sieve instead of the original. This controls the maximum size of the output shreds — anything larger than 4mm gets re-shredded automatically.

How to shred

Feed your failed prints into the shredder. Don't force large pieces — let the machine pull them in. The shredder does the work.

Large prints: You may need to cut up big pieces with a bandsaw first. The shredder handles small to medium prints fine, but really large pieces may bridge over the shredder and block the rest of the material from getting shredded.

Output

You'll end up with a pile of small plastic shreds, all under 4mm. But they won't all be the same size — and that's a problem for the next step.

Why sift?

The shredder produces a mix of fine pieces and larger chunks. If you feed inconsistent shreds into the extruder, you get inconsistent filament — blobs, thin spots, and jams. You need homogenous shreds for smooth, even filament.

The machine

I designed and 3D printed a sifting machine that fits directly onto an IKEA Samla box (22L). A NEMA 17 stepper motor shakes the shreds through a mesh. I use a 4mm mesh size as default. See it in action: sifting video · changing mesh size

How it works

Pour your shreds into the hopper. You may need to tap the hopper sometimes if the material doesn't flow well. The stepper motor shakes the mesh, and correctly sized pieces fall through into the Samla box below. Oversized pieces stay on top and get ejected sideways.

Why dry?

PLA absorbs moisture from the air, and it degrades when extruded wet. Wet plastic causes bubbles, popping, and rough surfaces during extrusion. This is especially important for recycled material because the shredding process creates a lot of surface area, which means more moisture absorption than a solid spool.

The machine

I use a VEVOR food dehydrator (1000W rated, ~600W average at 60°C). It's a standard kitchen dehydrator with temperature control and a timer. I bought 8 additional stainless steel mesh trays so I can dry larger batches at once.

Settings

Spread the shreds in thin, even layers across the trays. Don't pile them up — airflow needs to reach all pieces.

The machine

I use the ArtMe 3D MK3S desktop filament extruder (full DIY kit). This is the most finicky part of the whole process.

Settings

These are my settings — yours will be different. The ArtMe settings heavily depend on the specific filament and require fine tuning for each batch.

Check the ArtMe 3D website — the creator has excellent documentation on dialing in settings.

Expect a warmup phase

The extruder needs to groove in and find its equilibrium. The first ~5 meters will come out undersized. You need to stand there during startup, fiddling with the settings and the placement of the optical sensor until the output stabilizes. Once it's dialed in, you can step away and check occasionally.

Modifications I made

What to expect

Well-sorted shreds (same brand, same color) produce very consistent diameter. Mixed brands will sometimes have bumps and diameter variation — different PLA formulations have slightly different flow and melt properties. This is normal; see Step 5 for how to deal with it.

Why trim?

Mixed-brand filament has highspots — small bumps where the diameter exceeds 1.75mm. These bumps can cause jams in your 3D printer. The nozzle fixture shaves them off.

The fixture

I drilled out three hardened steel printer nozzles on a lathe to 2.1mm, 1.9mm, and 1.7mm. These are mounted in a 3D printed fixture. The filament runs through all three nozzles in sequence, each one slightly smaller than the last, progressively removing any highspots.

Use hardened steel nozzles if possible. Regular steel works in a pinch, but brass wears out quickly.