"Bob Hoover" wrote in message
...
On Mar 21, 12:10 pm, wrote:
On Mar 20, 6:49 pm, Bob Hoover wrote:

Of course it matters, Harry. EVERYTHING matters!

You can say that again.
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Okay :-)

EVERYTHING matters, Harry.

But I think Ernie said it best when he SPECIFICALLY mentions COOLING,
whereas I simply hop onto my Assumptionmobile and roar off in all
directions, ASSUMING you'll somehow KNOW that cooling is an inherent
part of the welding process.

Hot metal SHRINKS. First lessons for the Wannabee Weldor is tacking a
couple of coupons together. You lay them on the bricks a given
distance apart and perfectly parallel. The gap -- the 'distance
apart' -- is determined by the thickness of the metal and the type of
welding being taught. Stick, with quarter-inch thick coupons mebbe
4x6 inches, the gap is about equal to the thickness -- about 1/4 inch
(a fat 6mm for youse udder guys). Now simply move one coupon until
its LOWER corner - the one closest to your belt buckle -- TOUCHES the
other coupon. NOW strike your arc (MIG, stick or TIG) or create your
pool (TIG or Gas) and tack-weld that puppy. Go ahead; right there on
the corner where the coupons are touching.

Now let it COOL... and look what happened to your gap. Yes, you may
look under the bench for it. Or even frisk the student beside you (if
you can get away with it). But no matter WHAT you do, your gap has
vanished; gone forever.

Harry, SOMEONE HAS STOLEN YOUR GAP!

(Relax; it wasn't your fault... you aren't going to get Yelled At.)

What's interesting is the amount of POWER contained in that molten
puddle. If you're using TIG and haven't been given any filler rod,
you'll end up STIRRING the molten puddle until both coupons are
securely joined.

Then let it cool.

The first thing that happens is the puddle cools. In fact, we see the
puddle 'go out' like a little candle; it sort of FADES AWAY. The
puddle is still there but now it is COLD. Go on... touch it.
HAHAHAHAHAHA... gotcha! So the tiny pool of metal is no longer
GLOWING but it's still hot enough to make you a contender for the
Standing Broad-jump.

(Have you got one of those IR thermometers? You know; you just point
it at something and the read-out tells you its temperature... which in
the case above is probably about 400 degrees on the Fahrenheit scale.)

....so the golden puddle fades away... and so does the GAP. Because
just as hot metals MUST expand, so too must they shrink. So there we
are, a whole classroom of dummies wearing funny gloves and goggles
waiting for... THERE! Did you hear it? There goes another one!

Welding with TIG you can stir a puddle that's close to 4000 degrees!
(No, you didn't. I said 'you CAN,' not that you DID. Try to heat
mild steel to a temperature that high will probably set it on fire...
for a few seconds :-) The point here is that an electric arc is a lot
hotter than an oxy/acetylene flame.

What we were listening to were not crickets; it was the sound of metal
CRACKING as it cools.

A cracked weld is common with TIG, rare with gas. And since Harry is
using gas, I'll stop passing it and start talking about it.

Cooling of your weld -- the UNAVOIDABLE contraction of the metal -- is
the hand-maiden of the metal's expansion. The person doing the
welding must observe the rules to which the metal is subjected: Heat
makes it bigger, cooling makes it smaller. We must always be thinking
AHEAD of those processes. We KNOW they are going to happen so we must
allow for them.

Harry has gotten into clusters. If he were a student driver that's
about the same as his first exposure to freeways, off-ramps and the
dreaded Traffic Circle, because as Ernie has pointed out, the rules
for expansion and contraction must now be applied to inside angles and
outside angles.

And right about here Harry needs someone to shout in his ear: "YOU
CAN DO IT!" Because he can, although there will be moments... and
thousands who have tried, failed an quit! -- when he will think the
task is simply too much for him. He'll often have lots of good
reasons such as age, the state of his health, the conditions under
which he must practice... all kinds of GOOD REASONS for NOT learning
how to weld.

They're all bull****, Harry. You CAN do it. Not just lumpy little
tracks similar to something laid down by a diarrheatic rat, but a neat
'row-of-dimes' that is the hall-mark of a competent weldor.

Practice makes master of the man. That expression is as old as the
hills. Mebbe even older. It isn't something that needs explaining.
But in modern-day America corporate entities work very hard to destroy
such things, in order to replace them with cradle to the grave
dependency upon their particular brand of reality. The paradox here
is that having convinced everyone that mastery is now embodied in a
piece of paper will eventually leave no one to design the bloody
machines nor fix the old ones, when they break down. All they have is
legions of Graduates, rather vague young fellows who have a piece of
PAPER that says they are Master of all they survey. They will be in
their forties before they realize they've been lied to by their
corporate puppet masters. And by then it may be too late. Because you
balls the size of buffaloes to do what Harry is doing.

So keep practicing, Harry. Indeed, I envy you to the point of tears,
knowing what you have ahead, because once learned, it's never to be
forgotten.

-R.S.Hoover

Bob: As a point of interest, I found this letter sent a few years ago to
EAA by a Richard Finch. I've got a copy of the whole letter but I'm
reproducing just a portion of it here. It was an eye opener for me as a
rank amateur welder. While the main thrust of his letter was regarding pre
and post heating of the weld , the predominant use of MIG to the exclusion
of Oxy-Acetylene was something that I had never heard of before. Also the
post weld cracking of the TIG didn't seem to be much of a problem for him.

"While I was researching material for my new book, Performance Welding, I
talked to several current high-volume kit plane manufacturers, to see what
their production welding methods are today. I talked to Kitfox, Avid, Rans,
Wag Aero, and Piper and Mooney aircraft companies. None of them use
oxy-acetylene to build steel aircraft fittings or even complete fuselages.
They all use MIG (wire feed) welding and none of them post heat the welds
with an open flame welding torch. When I asked Dean Wilson, designer and
builder of the huge Explorer aircraft (with umpteen hundreds of individual
tubes welded in the structure) if he gas welded or pos--weld gas heated the
structure, he said, "Are you kidding? If I had gas welded and post weld
heated it, it would still not be finished, and it would not be as strong as
it is now." He said that he MIG welded it and left it alone.

I am a certified aircraft welder, and I worked for Ted Smith Aerostar as the
head of the welding department until they closed the Santa Maria, CA plant
We TIG (heli-arced) welded all 18,00 engine mounts in an eight year period,
for the Aerostar twin engine airplane and we never pre-heated any of them.
A recent check with the AOPA and the FAA shows that Aerostars have no
cracking problem in their engine mounts or any other TIG welds.

On the other hand, I later became the chief field troubleshooter for
Fairchild-Swearingen Aircraft, and all Metroliners had cracking problems
with their engine mounts. Fairchild Aircraft pre-heated and post weld
stress relieved every engine mount but they used copper coated welding rod
to TIG weld the turboprop engine mounts."



I have seen some post weld TIG cracks but not for some time either in 4130,
aluminum or stainless. I did have some cracking on a weld on a turbocharger
exhaust, but it was dirty and very hard to get clean prior to welding.

I'm enjoying the welding discussions. I've already won the standing broad
jump and the advanced dance of slag in the socks. Or how about the
reverberation where you recoil from the hot metal, hit your hand on the
adjacent tube and recoil back to the hot metal. Repeat until either the
weld cools or you just get tired of the process and quit. Of course I
should have had a glove on but it was just going to be one little tack.

Keep up the great information and do whatever it takes to handle your health
issues. Sources like what you provide are disappearing.


Stuart Fields