=-=-=-=-=-=-=-=-=-=-= article 1808 (line 78561) =-=-=-=-=-=-=-=-=-=-=
Newsgroups: rec.crafts.metalworking
Subject: Re: cutting with O-A torch
Message-ID: <1994May17.155720.1796@mlb.semi.harris.com>
From: jws@billy.mlb.semi.harris.com (James W. Swonger)
Date: Tue, 17 May 1994 15:57:20 GMT
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Organization: Harris Semiconductor, Melbourne FL
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 I've never tried to make a clean (nice looking) cut; however, I'll venture
some free advice based on my having cut up a car into small enough pieces
to fit into the trash cans.

 The pilot flame should consist of a bunch of small cones (green) and
a blue outer flame. You want a slightly oxidizing flame (no yellow).
The flame does not need to throw a lot of gas. In fact, excessive velocity
results in turbulence and a flame that wanders.

 There are two oxygen knobs and one gas knob. One O2 knob sets the max
flow from the cutting O2 lever; the other sets a baseline flow. I can't
recall which is which on my torch. 

 The cutting flow should not be very high either. By torchlight you should
see a straight, gentle stream of "clear" within the pilot flame. This
jet is what you cut with, it just sort of washes the metal away like a
stream of water washes away clay. You're not trying to blast it away,
but smoothly erode it. The stream needs to sort of balance on the cut point 
so that the entire face (the thickness of the metal) is evenly bathed in the 
oxygen. This will give the smoothest cut. It the stream plays too much on
the surface the kerf will be wide at the top and narrow on the bottom.
I like a slight forward rake (flame directed slightly into the direction
of the cut) but I believe textbook is straight vertical, and let the
stream develop its preferred pattern of flow. This will work out if you
have a smooth, steady style. If you are shaky, the kerf won't be stable
and you'll have to actively try to balance the cut yourselfby dithering
the flame (resulting in a less straight, but hopefully not much wider, 
kerf). There are O-A cutting fixtures which you might try to emulate.
These have a stationary cutting torch head which is fixed above a work bed;
the piece is slid beneath the flame, sort of like working a band saw.
With this sort of arrangement all you have to worry about is feed rate.
-- 
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