Re: Digest Number 2

On Sat, 8 May 1999 12:13:41 +0100, Andrew Werby <drewid@...>
wrote:

>[I've been dreaming about a large gantry router for a while now. It seems that
>surplus parts exist that would facilitate the construction of one of these,
>but no one source seems to have all the parts I'd need, and I'm hesitant to invest in
>a pile of parts that might not ultimately be the right size. Any words of
>wisdom on the best parts to look for? I'd like it to be heavy-duty enough to cut
>parts out of wood- foam doesn't appeal to me much, although I realize that urethane
>foam prototyping board makes good patterns (but is brutally expensive.)

Hmm, let's see. Time and constant watching are what it takes to go via
surplus, and realistically speakin (I dunno bout you, but me I cain't
afford a $20K+ router), given the expense of going any other way, that's
what I figure ANYONE (at least in our group) is up to, pretty much. So,
NO, nobody's gonna have most all the parts. I spent two years searching
and collecting the shafting, bearings, and ball-screws. Shoot, even
building one with NEW parts is gonna involve many sources. Lacking an
engineering job on the structure, I just figured something built around

>1"D shafting for X&Y (and say 5/8" for Z) and goodly sized linear

bearings for same would handle all the materials I was interested in,
namely alum & foam (some of which can be as dense as wood, BTW). The
ball screws are the same Pitch/Dia. as used on metal milling machines,
so I figure I'm safe on that end as well. In fact, the volume (and
therefore the cost, both new and surplus) of ball screws is enormously
biased toward the standard milling machine diameters, that it's unlikely
you're gonna find/need any other dimensions anyhoo.

The key is just to keep looking. And new SOURCES (as well as new
supplies at the usual haunts) are constantly developing. Some guy that's
never had/sold linear motion stuff bids for and gets a pile of stuff at
some auction, and suddenly he's a CNC hardware source. 6-mo later he's
sold most of it, and he's no longer "in the business". B)

>I'd be interested in discussing the pros and cons of other machinable materials.
>I've got a pile of surplus I-beams that I was thinking of using as a
>super-structure, because the compaint about most of these gantries is lack of rigidity in the
>traveling beam. But these things are heavy, so I'd have to find
>correspondingly bigger motors, I suppose.

Uh, "I-beams"? I trust you are talkin bout ALUMINUM beams? Even if so, I
don't think such overkill in the moving portions is either wise or
necessary. Many of the linear hardware guys (I'm talkin bout new stuff
now) have some VERY stiff alum extrusions for building the gantry
portion (not to mention the base T-slot table)

>The main reason I'm considering building instead of
>buying one of these (aside from basic skinflintery) is because the
>available units I've seen never have much z-axis- they all seem to be made
>for sign-makers.

Yup, I know whatchamean. And after wondering about this, AND thinking
about my own distinct interests/uses, I think this makes perfect sense.
See my 'summary conclusions' below.

>But with extra z-axis comes another problem- how to find end-mills long enough to
>reach? And even if they can extend far enough, are they going to be stiff
>enough to work? Has anybody dealt with this, and come up with a solution?

As to the first issue of much of what you see being "almost 3-D", that's
largely because, given the cost and market for new machines, they're
mostly purpose-built FOR sign-makers and engravers, and the "nearly 3-D"
routers aren't exactly in wide demand, except in the aircraft and race
car body industries, and these aren't large enough markets to find very
many "off-the-shelf" solutions.

Next, if you wanna take a BIG jump and look at the "truly 3-D" 5+axis
aluminum routers that have HUGE ball mills routing out gigantic contours
from billet aluminum, then you are REALLY talkin big bucks and special
clientele.

It's really not practical to do much beyond "almost 3-D" (shallow Z)
anyway, without some way to tilt the cutter/router, so worrying about
how long you can get mills isn't the real substance of the issue; it's
how steep are the contours of your 3-D part. Only modest contours can be
realistically cut with a simple 3-axis setup, so you may have to resort
to cutting lofts and then assembling the foam (or wood) pieces.

I planned/made mine with 24" Z travel mainly because I hope to add
another 2 axis and an air-drive cutter head at a later date, and because
even with only 3-D, in most aerodynamically oriented contours, you CAN
do alot of 'carving' with a simple vertical Z (because unlike general
'carving', the contours in aerodynamics don't/can't change rapidly; if
they do, that usually means high drag).

>How far along is your router project- any pictures yet?

It's currently entombed in a warehouse, with the rest of our non-profit
Experimental Aircraft Engine corp's shop, awaiting (for the last 5 mos)
occupancy of our new building at a nearby airbase undergoing civilian
conversion. The X-Y and gantry are finished (basically, all 3 axis), but
the motors aren't mounted, and the electronics is still in the
bench-test stage. When we get it re-assembled, upon ingress to our new
facilities, I'll get some photos for the 'shared files' area.

SUMMARY on the why's and wherefore's of largish gantry style routers:

I'm inclined to think that outside the well-defined requirements of
signage, the uses of such a beastie are diverse enough that you gotta
look upon your own design as "purpose-built", and that's why I think you
just WON'T find a developed "generic 3-D carving router" market in these
big dimensions. The market and requirements are just TOO diverse; this
is just as it should be, and just as most of us would like it anyway,
eh?

Gar