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Release status: experimental

Nice round holes.jpg
research on recycling RepRap parts into powder and HDPE
CAD Models
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Kitchen Food Processor

I've been thinking about trying a generic kitchen food processor - the appliance you use to turn 2 kg of carrots into shreds. I'll try it once I have a granule extruder built. --Sebastien Bailard 03:53, 22 February 2010 (UTC)

Fluid Suspension

Students at TUDelft found that putting HDPE in a blender along with some water helped bring the pieces to where the blades could cut them, so that they got smaller, regularly-sized bits, while simultaneously solving the problem of blades heating up and possibly melting the plastic, as the water conducted away the heat from friction. Their project report paper was available on the blog before, but the pdf link doesn't seem to be working for me today. --4ndy 17:36, 31 March 2011 (UTC)

Paper Shredder

A paper shredder with all the necessary locks and safeties removed is verified to work as a viable option for shredding plastics to a size where they can be used with granule extruders. More information can be found Here.

Lid System

Mason Jar

We can print a system that screws onto a large glass jar, or in some way uses a jar to store plastic.


We can print a system that attaches to a large bucket.

Cyclonic System

If we're using a solid receptacle rather than a cloth bag, we may want to use a cyclonic-type seperator powered off a vacuum or tiny electric fan.

Crazy Talk

Cooling idea, requires compressed air feed. Probably unnecessary.

Rotary Shaper

Forrest, if we can't solve the grit contamination issues with mechanical filtering, there's always a $10-15 microplane rotary tool that works with a drill press:,42524

Microplane rotary shaper.jpg

We can RepRap a machine built around the microplane rotary shaper and a corded drill, with an exhaust port. It would help to make it dishwasher proof.

Those rotary shapers are "discontinued - while stocks last" at that supplier. Maybe there's more milage in Surform plane blades which are cheaper and unlikely to disappear. The drawback is that they are flat, so would need a linear rasping/grating action. -MattyMatt

Secondary idea using shureform blades that I am investigating is to use 2 replacement blades (which are flexible to a degree) mounted in a circular pattern between 2 plates, one,the upper, solid and driven, and the lower spoked for chip exit. I am still working on paper plans, but when I get them transferred to CAD I will post them for feedback.

Aluminum Shredder

It seems like the Filamaker has come up with a pretty simple system for grinding plastics. But the price is ridiculous. Most of the device can be made with off the shelf parts except the blades. That's where aluminum comes in handy. It can be worked on with simple woodworking tools such as drills and saws. I just wonder if even thick aluminum blades would be strong enough to shred PLA and ABS

Grinder: Working Research Notes

Portable belt sander upside down.jpg

I've got the curling on HDPE prints down to something quite manageable. Last night I decided that I could dress down the remainder if I only had a belt sander. A little while ago, I went into town and bought a nice little Makita belt sander. It wasn't the cheapest, but it would lay, belt-side-up, quite firmly, which is what I needed.

It took about 15 seconds to grind the raft off of Bogdan's corner block for Rapman and dress off a few other rough places.

Plastic corner block.jpg

I bought a new little drum sander for my Dremel {~$4.50} and cleaned up the seating for the z-axis bearing.

Z-axis bearing seating.jpg

It also did a nice job cleaning up the hole for the z-axis threaded rod.

Nice round holes.jpg

One added benefit which might be the Rapman or might be the HDPE or might be the Skeinforge settings is the roundness of the horizontal holes in the print.

None of this teardrop nonsense.

I'm beginning to think that HDPE is a very serious contender for printing Mendel parts. It's

  • dirt cheap,
  • readily available,
  • strong,
  • doesn't make nasty fumes
  • AND now we know how to work with it.

I expect that polypropylene, which is cheaper still is going to be just about as good.

Now here is the serendipitous Christmas present. That Makita belt sander grinds HDPE a treat and puts it in a little bag, or a big one if you want to sew one.

Guess what? The problem of grinding plastic so that it can be recycled into filament has just gone away. Virtually any kind of GranuleExtruder can eat plastic powder. It takes a heftier one to use 3 mm pellets or shreds of a similar size.

Build yourself a slope-sided hopper on top of that Makita and your grinding problems are solved. When you wear out your belt, go down to your hardware store and buy another. The Makita uses a 3" x 18" belt and it costs a bit over a dollar. No difficult-to-sharpen, never mind dangerous, macerating blades.

God Jul, everybody!  :-D

(Writer: Forrest Higgs)

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