From: Charles.K.Scott@dartmouth.edu (Charles K. Scott)
Subject: Oxy/Acet welding problems
X-Posted-From: InterNews1.0a5@newshost.dartmouth.edu
Organization: Dartmouth College, Hanover, NH
Date: Tue, 26 Jan 1993 14:01:43 GMT

I'm into a long term building project that involves many different
skills; woodworking, welding, engine building, cable stringing and
fabric.  Yes, it's an airplane.  At the moment I'm having difficulty
with the welding part.  I've got a set of Smith guages for the torch
and while they seem to work OK, what I'd like to discuss is the
pressures to use.  I've had a little experience welding as an auto
mechanic, but no formal training. I've read a number of different books
on welding and I just never seem to find any information on precise
pressures to use.  Maybe it's because there is a need to change them
for different materials and thicknesses, I don't know that's why I'm
asking.  Specifically, the material I'm welding is 4130 sheet steel
.080" thick.  I finally decided to go to the local welding supply shop
to make sure I was using the correct tip and they called a Smith
dealership.  The dealership was happy to sell me a new tip which
appears to be the smallest they make.  There is no way this tip works
for metal this thick, I can't imagine what was going through their
minds to recommend so small a tip.  I wonder if it's even going to work
on the thinwall tubing that's .035".

I have several other tips, one of which seems appropriate (confirmed by
a friend who truely does know about welding) but I'm still stumped by
pressures.  My friend always used 5psi (Acet) and 20 (oxy).  I've had
difficulty using these pressures.  In desperation I finally just start
fiddling with the regulators and now have about 8 and 15 respectively.

Here's the question: Is there a specific pressure to set the requlators
for  welding?  I know what to set for cutting, that's not a problem. 
Cutting is easy, welding requires delicacy and skill.  When welding
aircraft parts, good enough isn't good enough.  It must pass inspection
or it can't be used.

The welding I'm doing requires me to weld one piece to another at a 90
degree angle.  I have to bend a piece into a U shape and weld the U to
a plate.  I've discovered that welding into the angle isn't easy and I
must be missing something in the set up.  I haven't been happy with the
bead yet and my friend, who has built several aircraft confirms that
they are not satisfactory.  What would be recommended to place the work
on so that the heat isn't wicked off.  Would firebrick be a good base?

I'm also using a 1/16" rod which my friend also says is incorrect, he
feels 3/32 would be better.  1/8" is too big.

It appears to me that a lot of things have to come together to make a
satisfactory weld.  The books I've read on aircraft welding say that
the rod is dipped into the puddle and kept there and the puddle and rod
and tip are all moved down the area to be welded in one fluid motion. 
Easier said than done, I haven't achieved this ideal yet.  One of the
problems, among the many, is that I have to use so much heat to get
things molten that the hand holding the rod gets too hot and makes me
jumpy which doesn't do any good for my steadiness.

Man, this is getting involved, sorry.  Let's just start one thing at a
time. Is there a specific pressure setting for the regulators and does
it vary according to the thickness or type of metal being welded?

I'll deal with the rest of the stuff as the discussion evolves.

Thanks anyone who can assist.

Corky Scott
Newsgroups: rec.crafts.metalworking