Re: RepRap (was RE: [CAD_CAM_EDM_DRO] Re: Fab@Home)

On Wednesday 10 January 2007 21:38, Pete Brown (YahooGroups) wrote:

> I don't get the self-replication aspect.
>
> I thought, perhaps incorrectly, that no machine can replicate itself due to
> work envelope restrictions and compounding errors.
>
> For example, if you have a machine with a 5x5 work envelope, the leadscrews
> or at least the ways would be larger than that, and couldn't be replicated
> in a single piece. If they were multi-piece, they'd be too inaccurate.
>

It looks as though the current version of the 1.0 model is going to have
threaded rod. Threaded rod is hard to print, so we're going to buy it off
the shelf. But eventually we want to go to rack-and-pinon. And for that, we
can print it.

If we need a rack 1 unit long, we can print it in a machine with a print
volume .95 units on a side, just by printing the object oriented laying
diagonally on the bed of the printer.

But in the end, there's always going to be some elements it will just be
easier to buy off the shelf, like drill rod, motors, and microcontrollers.

>
> And even if you get past that, the inaccuracies in the machine (only
> theoretical machines will ever be perfect) will be compounded much like
> copying from an audio or video tape which was copied from a tape which was
> copied from a tape leaves you with a noisy crappy tape :) This will be true
> whether the limitations are design limitations (like low res) or errors
> (like backlash).
>

This is where gauge blocks and calipers come in, just like with normal machine
tools.

>
> I looked all around the reprap site and saw no reference to this, so
> forgive me if this is a FAQ.
>

I'll check and add it if necessary.

>
> In response to the comment about one being just a router with a syringe:
> while it certainly looks like there is some competition / animosity between
> the two groups, it is obvious to me that neither is a good or usable
> machine at this point. The resolution is so low as to make them good for
> experimenting only. Perhaps in a few (machine) generations they'll have a
> higher resolution, but I think you'll quickly run into a wall. There are
> reasons the high-res commercial units cost so much. It would be nicer if
> the two groups pooled ideas, but just because something doesn't follow the
> free/open source mantras doesn't mean that the creators are evil :)
>
>

Not exactly animosity, we're each just doing our own thing (and boggling at
the other guys' design choices). And their project is open too, they're
using the BSD license. I hope we'll merge with them eventually. (I don't
know which makes the worse neologism, FabRap or RepFab.)

For resolution, we don't want to go too low right now. We're putting down a
bead of filament around .5mm diameter, with .1mm positioning accuracy. If to
we went to a filament half that diameter, everything would take four times
longer to print. (It's like painting a wall; it takes longer if you use a
tiny brush.)

Eventually we will want multiple nozzles. Right now a support material print
head is a much larger concern.

>
> Pete
>

Regards,
Sebastien
RepRap.org

>
>
> _____
>
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Sebastien Bailard
> Sent: Wednesday, January 10, 2007 3:12 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: Fab@Home
>
>
>
> Hey folks, I was discussing this with a pal of mine, the fellow who wrote
> ArtOfIllusion:
>
> On Wednesday 10 January 2007 01:14, Peter Eastman wrote:
> > You're probably already aware of this, but it looks like another
> > project with similar goals to RepRap:
> >
> > http://www.fabathom
>
> <http://www.fabathome.org/wiki/index.php?title=Main_Page>
> e.org/wiki/index.php?title=Main_Page
>
> > Peter
>
> Yes, I'm aware of that group's work. We exchanged some cordial emails with
> them a few months ago, at my instigation. They've done some fairly
> impressive work. One thing I like about their setup is that they can
> fabricate most of their frame out of acrylic using a CNC router/signmaking
> shop. This something we've discussed, but shelved for the time being.
> (They've got a beautiful new CNC router over in the Carleton architecture
> dept., but I haven't wrangled access to it yet.)
>
> This was Graham Stabler's (of the CAD_CAM_EDM_DRO mailing list) take on it,
> which feels a bit harsh even if there's nothing in it I can really disagree
> with:
> "[CAD_CAM_EDM_DRO] Re: Fab@Home
> A laser cut perspex CNC router with a syringe. It seems silicon
> sealer might have been the nearest to an engineering material it has
> laid down. Not getting overly excited here but I do like efforts
> towards low cost rapid prototyping.
>
>
>
>
>
> [snip]
>
>
>
> [Non-text portions of this message have been removed]