From: "John R. Johnson" <john@siu.edu>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Learning to Weld. Practical?
Date: Thu, 14 Aug 1997 14:33:52 -0500

Right.

There are a few ways to weld.  You can use a MIG, a stick welder, a TIG,
and/or a torch.

MIG the quality of the weld is determined solely by the quality of the
welding equipment used.  The penetration is determined by the temperature
setting and the consistency of the temperature, which again goes back to
the quality of the equipment.  As for operator skill, a friend who is a
professional MIG welder said "Can you use a ball point pen?"
Excellent for commercial welding of standard mild steel, such as truck
bodies, etc.

Stick welder -  This is the old familiar arc welding "buzz box" with a
transformer and leads.  You use coated rods to protect the weld area from
oxidation.  Excellent for routinely sticking chunks of iron together.
Not at all acceptable for aircraft work.

TIG welding.  This is essentially identical to gas welding, but the heat
if supplied by an electrical arc whose temperature is controlled by the
amperage setting on the welder.  You use the heat to melt the pieces
together, adding filler rod as required to control penetration and weld
quality.  OK for aircraft use.  Welded area require normalization after
welding to draw the temper and regain the toughness of the 4130 steel.

GAS welding.  This is the traditional welding process for aircraft.  It
is probably the best process for a homebuilder.  Heat for welding is
provided by a "close to neutral" oxygen and acetylene flame.  Penetration
is controlled by the size and rate of travel of the weld puddle.  You can
play with it until it looks the way you want it to look.  The only serious
problem is excessive heat embrittling the 4130 tubing.  After completeing
the weld play the torch around the area to cool it slowly to the proper
temperature for normalization and you can weld and normalize in one step.
Simple guidelines are:

1.  Start the puddle before you add rod.
2.  Add rod by dipping it in and out of the puddle.
3.  Move the puddle where you want it to go with the torch flame.
4.  Use the tip size that will start a puddle in about ten seconds.
5.  Never dip the inside cone of the flame into the puddle.  Keep the
      tip of the inner cone just above the puddle surface.
6.  Adjust the flame until the inner cone is sharp and visible.  Then
      turn up the gas until the cone just grows a feather and turn it
      back down until the feather just barely disappears.  If you are
      welding stainless, leave just a little bit of feather.
7.  Match the rod to the metal you are welding.
8.  When welding aluminum use flux and keep moving.
9.  Never move the flame away from the puddle.  The puddle should be
      within the flame as long as it is molten.
10. If you make a hole, build it back from the sides by welding onto
      the edges with the filler rod.  ( should match the base metal )

11. Practice until your welds look good.  Then weld a joint and hammer
      it flat.  If it cracks you didn't do it right.  The old welders
      test was to take a large piece of tubing and cut segments from it
      to make a ball.  Weld up the ball.  Put it in a press and flatten
      it after it is all welded up.  THEN pressure test it.  If it leaks
      you flunked.  Practice some more!  That was the test we had to pass
      to be a journeyman pipe fitter when I was a callow youth.

John