ATM - Abrasive Water Jets (long)

[Adam Perkins <scopeguru@yahoo.com>]

Hey,

I dropped in on my local abrasive water jet cutting shop and asked a
few questions today, I thought I'd pass along what I learned.  I didn't
want to waste to much of their time, but did learn a few things.

The shop I visited has a single machine that they do all of their work
on.  Its a dual axis CNC machine.  That is, they can cut any shape out
of flat stock by directing the cutting jet by computer.  Anyone who has
ever seen one of those older pen plotters draw something knows how this
process looks.  The cutting nozzle rides back-and-forth on a rail(X
axis), which in turn moves on a track (Y axis).  The bed of the 
cutting machine is big, more than enough room for a 4x8' sheet of
material.  They can accept DXF or Autocad files, although a simple
shape like a circle doesn't require much preparation for them.

An X-Y axis machine is apparently the norm for this industry, so no
bevels can be cut. The cut they provide  looks like a perfect 90 deg.

The "jet" which does the cutting uses a very high pressure stream of
water loaded with fairly fine grit (I asked if it was Silicon Carbide
and got "yeah, like that..." as a reply).  The slurry comes out of the
nozzle at a ridiculous speed and cutts very quickly.  The few pieces of
cut glass he had on hand to show me were only 1/4" thick, but had a
very nice edge to them.  I think a little bit of smoothing might be
quickly done by hand, but might not even be necessary.  The thin
samples made it hard to judge.  The kerf of the cut is approx. 1/16" of
an inch.  I asked about coring a blank, and was told that it can be
done, although glass is harder to do this with than some materials. 
They prefer to come in from the side when possible (not possible in our
case...)  You would probably have to sacrifice the core.

Apparently circles are no big deal for the operator to make (CNC
devices are very cool in this respect), and there is not much of a
setup fee even for a one-time-only service. 

The guy I spoke with said they can cut material up to 5" thick (nobody
here has a source for 5" pyrex???).  

The price is worked up on a "per job" basis, but I was told it
basically works down to a price per inch of cutting for simple shapes. 
The cost goes up for harder  and thicker materials.  The guy I spoke
with didn't know for sure, but though pyrex might be cut for the same
price as plate glass.

I explained that I was shopping around for a way to cut plate glass
into disks an inch or two thick. For my hypothetical 20" disk cut from
1" plate glass, I was given an estimate of $60US.  This sounds pretty
good to me.  Assuming a per/inch charge, thats about one dollar per
inch of cutting for 1" Plate Glass.  You could cut out lots of 6" disks
for $18-20 each from a big sheet, but might pay a lot more for just one
or two.  I think it would be worth the price to cut some small blanks
from the corners of a piece being cut into a big blank.

Overall, I got the feeling like this is a realistic and cost effective
way to chop up a big piece of glass.  I don't know how common these
shops are, but I know sign makers use the process alot.

I'd be interested in hearing from anyone who has done business with one
of these shops.

Hope someone was interested in this.

Adam Perkins
Covington, Louisiana

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