Re: [CAD_CAM_EDM_DRO] Re: Open (i think) design for a parallel robot (reprap may be interested)

"Dennis Schmitz":

> Speaking of which. I think the reprap machine could make strong structural
> elements out of that plastic if they laminated it with some glass fabric.
> With a 90deg rotary table they could make fiberglass tubing.

Hmm... That is a thought, like the new carbon fiber fuselage barrels on the
Boeing_787, (or conventional fiber tubing, I just think the new planes are
cool).
http://en.wikipedia.org/wiki/Carbon_fiber_reinforced_plastic#Supply_constraints
http://en.wikipedia.org/wiki/Boeing_787
http://seattletimes.nwsource.com/html/businesstechnology/2003049536_dreamliner09.html

It seems very complicated, but worth considering after getting the thing to
work.

"Ron Yost":

> On Friday 01 September 2006 00:28, Ron Yost wrote:
> > Is it just me, or are there others wondering what these machines are
> > intended for?
> >
> > How can the apparent goal of self-replication (of a largely metalic
> > machine) be
> > accomplished by squirting layers of hot-melt plastics? Or carving foam??
> >

If you look at the pictures of the extrusion head and Ed's ARNIE.
http://reprapdoc.voodoo.co.nz/bin/view/Main/Version2OfThePolymorphExtrusionHead
http://reprapdoc.voodoo.co.nz/bin/view/Main/ShowCase
I admit, there's an awful lot of metal there. We'll eventually eliminate more
and more of it, but we'll never get rid of that little brass nozzle at the
end, because that's going to be at or above the melting point for the
plastic.

Right now, the point isn't to make a perfect Von Neuman machine. It's to make
a practical one. And that means it's ok to include off-the-shelf items like
stepper motors or drill rod.

That's plastic's really damn tough stuff, by the way. I wouldn't feel
uncomfortable using a tool box made out of it.

> > They're fascinating to watch .. but other than rapid-prototyping (making
> > plastic
> > models of things), and/or as a conceptual challenge, of what utility are
> > they for getting -real work- done??? Or is that not the point?? Is it all
> > really academic for you folks? Engineering student toys, in other words.
> > That's how it sounds to me, so far. Maybe it's enough to get it built and
> > moving, with little thought as to what can actually be -done- with the
> > thing?? A useless robot, in other words. But utility may not be the
> > point. In which case, why is the whole thing relevant here?
> >

The point is not making models. The point is making anything you've got
laying about that's made out of plastic. Like your laser printer needs a new
plastic gear, or you need some new drippers for your irrigation line. Or a
bunch of sewing machine parts.

You can use it to make other tools, too. Like a wire EDM machine,
hypothetically. We've shelved the "Slap a wire EDM head on the RepRap" idea
for now. But, for example, Graham's going to put his work up online, and I
will hope we'll be able to make most of the parts of plastic.

> > Things have to be really beefy to do heavy, yet precise, work in steel,
> > and I don't see how eliminating mass is going to work at all for us home-
> > shop types doing metal. Plastic bearings wouldn't last long at all,
> > either.
> >

We aren't planning on using the RepRap to do subtractive fabrication work in
steel. It's not for throwing chips. It's for additive fabrication.

Here I think your note starts to segue into a discussion of the general merits
of hexapods for conventional machining. I'll leave that to the experts. I
don't know if you can use the stiffness of the tripod/hexapod to make up for
the lower mass, or what the mechanics are there..

There is one thing to keep in mind. We're hoping to have a slurry deposition
head working soonish. That will be able to deposit titanium nitride, other
ceramics, aluminum powder. We'll do it layer by layer, or slip-cast into a
plastic mold, but pop that in a furnace/kiln to sinter the particles, and
you've got a hard finished piece. Which should impress the folk who aren't
impressed with plastic. (

> > Yes, I know a tripod is a very strong structure. And I do get the concept
> > of the things. But, there has to be mass somewhere, doesn't there?? How
> > can a decent spindle holding real milling cutters hang off spindly legs??
> > Or is there a 'scale' thing here I'm not getting?
> >
> > I DO admire those who think out-of-the-box, tho. And I sure hope you
> > smart folks can come up with a revolutionary home-built, -useful- for
> > everyday work, machine.
> >
> > Ron Yost .. looks at his quaint mill and lathe and ponders the universe.
> >

Right now, we're looking at making a machine that will make whatever you want
out of plastic, given the constraints that it's going to be made from .5 mm
filaments and will have to fit in an initial working volume of about 30 cm on
a side. But the project lead used his conventional RP to make a peristaltic
pump for the slurry head, along with a slurry-filed-syringe-squeezing device,
and if every group member had a working RP, we'd be a lot further ahead.

I wish I had a bigger mill and a bigger lathe, and I think there will always
be a place for them. (I only hope I'll be able to convice my wife of that.)
But for stuff on the 30cm scale, we're going to find rapid prototypers really
useful. And kids will discover the things, and start working with their
hands again, which should be interesting.

Regards,
Sebastien Bailard