Saturday, December 05, 2009

Killing flocks of birds with one stone

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.

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

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

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 extruder 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


Josh Kopel said...

Belts like this tend to throw off a lot of abrasive particles.
Do you think the extruder will get damaged from the abrasives?

Forrest Higgs said...

Good point. I'll have to think about that.

Guy said...

Hmmmm... density of plastic relative to water? Density of grit? (most likely alumina or quartz) Should rinse out good, dry in an old food drier or cheese-cloth sack. Or do like a farmer and winnow the grit out.

Forrest Higgs said...

I was thinking of winnowing, actually. That's how you usually deal with two different materials that have notably different densities.

Unknown said...

Now we need to figure out how to print a belt sander ;)

Great work though. How hard is it to modify the current rapman or mendel extruder to take a hopper of plastic powder?

Forrest Higgs said...

I don't like the notion of going directly from powder to print. I intend that we make 3 mm filament as a common feed stock.

Joel said...

>Now we need to figure out how to print a belt sander ;)

The folks at Factor e Farm would probably be willing to collaborate.

>I was thinking of winnowing, actually.

Cool! Speaking of farm tech, here are plans for a basic winnowing machine...looks like a cinch to replicate, although the air impeller may be a little bit fiddly if you want to buy a bare motor rather than a blower.

Unknown said...

In this case the winnowing could be accomplished as in a popcorn air popper. Blow the plastic-grit mix up a length of piping long enough relative to the air volume and speed to allow the grit to drop out to the bottom.

solsken i syn said...

Great news, just how difficult do you think it would be to go from (supposedly clean) plastic powder to 3mm filament?

also if you, for instance, put the belt sander vertically and then feed the plastic diagonally from above

... pour granules here!
/O\ / /
| | /./
| |/./
| |./
| |/
| |powder comes here

wonder if small granules would get stuck or sneak through without being grinded? adding a shaking sieve might solve that or one could leave it to the winnowing?

When using new feedstock (as opposed to recycling) would it be necessary to melt the granules into larger objects? like a long stick to feed into the hopper?

Unknown said...

My question is: Hod do you get to stick the HDPE on the bed? Do you have a post indicating this challenges? I tried to print with HDPE with no success at all...

Forrest Higgs said...

Angel: You print ABS on an acrylic print bed, HDPE on a polypropylene print bed and polypropylene on an HDPE print bed. :-)