Crazy Horse jet finishing torch

["Simon Brown" <moonsong@zzzzzzzzzzzzzzz>]

Hi Tim,
I'm no expert on oxy-acetylene cutting, but I have used it to texture
granite. My workplace retains a maintenance fitter who has helped me to
operate the gear - perhaps you could locate a friendly metalworker who could
loan you some equipment and offer advice? Have a go on some scrap stone - I
have used several types of tips, depending on the area to be covered,
ranging from a fine brazing tip to a gas axe, and an 8" wide sparging tool.
Whatever tip you use, keep the flame moving so the heat is spread out. The
larger the rock, the less you have to worry about the heat sinking in. If
the gas balance is not right, the flame is too cool and only leaves carbon
deposits on the stone.

Oxy-acetylene not really appropriate for carving stone, as George
identified, because the stone can split if it is heated too much. A few
years back, I had the idea that an oxy thermal lance would be great for
waste removal, so I arranged for a demo in the boilermakers' workshop. The
thermal lance was developed in France during or after WWII to demolish
concrete bunkers and sunken ships etc. It consists of a steel pipe filled
with smaller steel tubes connected to a source of compressed oxygen. The
oxygen is fed through the pipes under pressure, the end of the tube is
ignited, and the resulting fireworks show pushed through whatever needs
cutting. The tool works by the steel tube burning in oxygen (even
underwater) which melts anything, and the gas pressure blows the hole clear.
The trouble with granite is that it froths when melted, so quite a bit of
molten rock gets sprayed back in your face. I tried it on a few small rocks,
(very spectacular!) but the rocks split as they cooled. Definitely a
demolition tool only! Who needs therapy when you can play with this
equipment?

Compared to a diamond saw, the oxy-acetylene cutting gear removes material
relatively slowly because the torch is really a surface treatment. Think of
Crazy Horse Memorial - penetration is achieved by drilling, waste removal by
blasting with detonating cord, while the jet torch is reserved for surfacing
to remove drill marks.

I have used the sparging tip for surface treatment of a massive pillar,
holding the flame at about 15 deg to the surface with the flame pushing out
ahead of the tool. I have also used it to exfoliate granite slabs in
combination with a water spray for cooling. The water spray was necessary to
control the heating of thin slabs, which are liable to crack if the heat is
allowed to sink into the stone. In the case of slab surfacing, the water
spray (a $5 garden lawn spike) was brazed to the sparging tool and the tool
was run backwards, so the flame heated and exfoliated the granite, which was
then immediately cooled by the water spray following closely behind.

Full safety gear is essential, and keep a fire extinguisher handy. Like
George says, keep the area around cleared of flammable stuff. When I was
using the sparging tip, clouds of fine, gold mica were released that floated
behind my face shield and stuck to my eyeballs - just like Lucy in the Sky
with Diamonds! They didn't hurt, but you may like to wear a respirator in
case of silica fume.

George, your story of being laughed at reminds me of when I carelessly
dropped a cigarette butt down my own Wellington boot in front of workmates.
After much hopping around and cursing, I got the boot off and shook the butt
out, only to have it drop into my other boot. Now I have matching socks with
a hole in each ankle and scars to match the socks.

Regards,
Simon moonsong[AT]optusnet.com.au