Friday, December 08, 2006


Some Thoughts on Available Materials (and Some Blue-Sky Thinking)

I was tidying up the house a bit the other day and realized that a huge amount of the mass contained within the house was essentially unwanted material. Here's a list of the various waste materials I noticed:
- glass (bottles, jars)
- paper (newspapers, junk mail, wrappers)
- cardboard (boxes)
- steel (cans)
- aluminum (cans)
- polystyrene (styrofoam inserts, packing peanuts)

Now, these aren't exactly ideal materials for RepRap. On the other hand, there seems to be a near-endless supply of them. Some of it might be adapted for use as suppor material, or possibly filler. Maybe there's more potential than that.

Not exactly sure where I'm going with this. I suppose, ultimately, I'd like to see an Nth generation RepRap that can take this detritus of modern life, sort through it, break it down and build more interesting items.

Sure, that's well beyond the current capabilities but, then again, I remember what the first generation of Linux looked like. And that was, what, 15 years ago? It's not hard to imagine a RepRap capable of building add-ons to itself to the point where the RepRap "kernel" is almost invisible, hidden behind more user-friendly layers of hardware. Almost no one who uses Linux now interacts directly with the kernel. It's possible that, in 15 years, almost no one will spool their own filament, or even care what filament is.

Should be pretty straightforward. You can convert the paper and cardboard into sugars and go from there to PLA, or you can use them as fuel to power your reprap. I'd throw in the polystyrene, except iirc it produces some nasty combustion products.

From there you can use your energy to power your reprap to make molds for the aluminum, steel and glass and use the energy to run your Gingery furnace to melt those.

There's a problem here? :-)
yeah thats really awesome.

dunno if you mentioned it, but theres tons of HDPE floating around in the form of bottles and other plastic crap.
True. Lots of HDPE (milk bottles and grocery bags) PETE (soda bottles) lying around.
There certainly is a lot of HDPE around that could be recycled. There are several technological hurdles that we have to get over before we can tap it.

1. We haven't demonstrated that we can run it through a Mk II or something similar. I can certainly get you 3 mm HDPE filament from the plastic welding rod people if anybody wants to seriously take on that task.

HDPE has higher melting and processing temperatures. It also has, iirc, a melt index a magnitude lower than polycaprolactone or PLA, which means it is going to be harder to extrude either in a Mk II or into filament.

2. We have yet to develop either a plastics grinder to recycle plastics or a filament extruder on a home scale. Mind, we've done a lot of work and more thinking about the extruder question, but we haven't got one. Anybody on to take on either of those two tasks?
One thing that might provide us with a way to handle HDPE is to make the machine do shape deposition manufacturing, which is basically what you get when you interlace a low-accuracy FDM process with milling. It might be possible to keep the forces down by using a small cutter and low feed-per-tooth; and then we could use a much, much larger extrusion head to deposit the HDPE. You could also have this variation hold the part by building it fused to it's working surface, then cut it off with a hot version of something like the wire a potter uses to free something from the wheel, and then uses the endmill to refinish the surface.

I am starting to think that SDM is rather the way to go for higher performance reprap versions. It wouldn't entirely surprise me to see, a bit down the line, a metallic reprap with an axis set capable of dealing with full-on machining forces, doing SDM with steel. Certainly not appropriate for everyone, but might be very appropriate for some.
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