wrote:
On Thu, 26 Dec 2013 08:55:28 -0500, "Mr. Luddite"
wrote:


TIG welding is an art form to me. I learned to use both TIG and MIG
welders, although my welds look horrible compared to the highly skilled
and certified welders I've known over the years.

In the business I was in, the large (up to 120" square) vacuum chambers
are constructed of half-inch thick (or thicker) stainless steel plate.
The welds required for vacuum integrity all have to be TIG welded to
ensure 100 percent root penetration to eliminate any microscopic voids
or cracks. You could hold liquids with no problem with these
microscopic cracks because the molecules in the liquid are larger than
the cracks ... therefore no leakage. But to many gases in the
atmosphere the same crack looks like the Grand Canyon.

We put "stiffeners" on the chambers to add the required wall strength to
withstand a 14.7 psi pressure delta. A 60" square chamber under vacuum
has about 26 tons of force per side trying to crush it like a tin can.
Those welds were structural only and therefore could be MIG welded.

Watching the quality of the "bead" that some of the welders could lay
down over a long distance was amazing. Tedious work, but critical to
the vacuum integrity of the chamber.


TIG is the welder of choice for pontoon boats around here and that
work is steady. A guy with a TIG on a truck can easily charge $100 an
hour or more, usually with a 2 hour minimum. I do understand it is an
art. The quality of the weld you can get makes it worth learning tho.
I started with a stick welder and once I get in the groove I can lay
down a decent bead. I usually have to practice for a while before I
start on the real work because I don't really weld that often these
days. If I am serious about it I put my rods in the oven at low heat
for a while to get them dried out

You can practice a lot of TIG technique with oxy/acet gas welding. Very
similar, but TIG has better heat control.