[TheForge] Miniature air-arc

[Kathy]

To L Brown,
Yes, but it's a minor item that will be thrown in for thoroughness; also, it
wasn't an invention of my own. Therefore, I don't mind blabbing on the net about
how to build one, but on the other hand will not go to the trouble of providing
a drawing until I construct the equipment for the chapter on air gouging in the
book. Furthermore, I haven't built a miniature air-arc torch in thirty-five
years, so my memories may be less than letter perfect; for instance, I remember
the DC current used as about 65 amps and the air pressure as 45 PSI, but your
results may vary. Don't use too much air pressure, as the vibration it creates
will snap your carbons off (see needle valve advice further on). 

Before constructing an air-arc, you should know that the practical difference
between 1/8" and 5/32" copper clad carbons is small (unless you are building the
power source), but price differences are extreme (5/32" carbons can be found as
low as $7.50 per box, but no discounted 1/8" carbons are available). Since this
air-arc torch design uses one size only you may wish to switch to the 5/32"
diameter (I will be using both for joining and so will build the 1/8" air-arc
version for that section of the book.

In the old days, we would cut the back off of a #4 (oxyacetylene) cutting tip
and drill it out to size for the carbon electrode. Use a slightly loose fit to
avoid breaking off the delicate rods in the tip, and order your carbons before
buying your drill bit. Do not attempt to work your way around using a cutting
tip, for its multiple holes are central in achieving the sweet performance you
can expect from this device.

The back end of the tip was either turned and tapped for 1/8" National Pipe
Thread, or else brazed to a 1/8" NPT male fitting. The fitting was then
cross-cut in an "X" pattern down the length of its thread, so that turning a
female fitting on the thread would cause it to clamp down on anything passing
through it. Here, my memory becomes hazy; I think we used to employ an internal
spacer (ex. the ball from a pipe compression fitting) between the carbons and
inside of pipe in order to span the diameter differences. However, you may use
any gentle clamping method (ex. TIG torch parts) that you find convenient. You
may even find smaller pipe fittings at Smallparts.com (hint, hint).

Having completed the torch head brings you to your next decision. Are you going
to keep the device small (for storage in a tool kit), or are you going to build
a deluxe unit with ergonomics as your top priority? Assuming small, then your
next step is to attach (braze) it to a flat piece of copper (even flattened
copper tubing will do) for old fashioned clamp type electrode holders, or else
braze it to the top of a stripped down twist top electrode holder. 

If you're going with the deluxe model, you would attach the air-arc to the top
of a welding whip, which you would either construct yourself (there must be a
hundred electrical experts on this list to give you advice on where to find
flexible wire for the purpose) or order such a whip from a welding supply house.
At this point, we should pause and ask just how far we are willing to go in
building the deluxe (ergonomic) model, for the advice I've just given leaves you
needing to deal with two leads; one for current, and the other for air. If you
want to build the best possible tool it is better to use just one lead, as is
seen on industrial air-arc torches. Clear flexible tubing is available at large
hardware stores. A small such tube can be run inside a larger exterior tube,
with flexible copper strap (heavy wire wick can be used for the purpose and is
sold in small rolls at electrical supplies). How you arrange hose barbs and
clamps, turn metal fittings, or carve and glue wood or plastic fittings to
separate the air from the electrical connections is up to you (I haven't got
that far in the book and don't expect you to wait on me).

Which brings us to the air in air-arc torches; with the compact models, a short
section (two or three inches) of flexible copper refrigeration tube is brazed
into a hole drilled near the back of the torch head (just forward of the NPT
thread). A 1/8" or 1/4" threaded cap or plug is brazed to the other end (buy
your needle type air valve first, and then suite your fittings to it. DO NOT USE
ANY OTHER KIND OF AIR VALVE--NEEDLE VALVE ONLY.

I'm not going to get any more specific than this because the details of my
designs change a hundred times before construction ever begins. I'm not in that
chapter yet, and have no intention of being reduced to writing and drawing at
2AM because my mind won't shut up :-)

Copper clad 5/32" x 12" carbon electrodes are available in 50 count packs (item
#BWS22-983-003X) from Weiler Welding ($7.50) 1-800-526-9353 Home page:
http://www.weilerwelding.com/index.htm 

Do not use an air-arc without at least wearing a two-string air filter, unless
you like carbon-lung. Don't run an air-arc in your garage without a friend
standing by with a water hose.   
Mikey

-----Original Message-----
From: theforge-bounces at mailman.qth.net [mailto:theforge-bounces at mailman.qth.net]
On Behalf of Larry Brown
Sent: Saturday, June 23, 2007 3:35 AM
To: Sponsored by ABANA
Subject: RE: [TheForge] oxy-propylene, propane tips and air-arc


Back in my day (pterosaurs still flying), every welder at
Boing Boing Airplane Company constructed his own miniature air carbon-arc 
(1/8" carbons); we could carve a few thousandths of an inch off a weld bead with
them quite easily.
Mikey

Any plans for it in the next book?
Sounds handy.
L Brown

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