> > > Hello Gang

 > > Years ago I used to worry a lot about aircraft companies using MIG
 welders on their
 > > 4310 frames and components because of all the valid reasons mentioned on
 this tread.
 > > Since then, I have studied a couple of dozen wrecked Kitfox, Avid and
 other 4130 tube
 > > framed aircraft and found when these planes crash, the frame tubes
 always break or
 > > bend near the middle of the tube. None ever failed at the weld.  Faced
 with these
 > > facts, I pushed my opx-acetylene outfit in the corner and went out and
 bought a MIG
 > > welder for my frame work.
 > > John Larsen

 For the most part, I agree, John
 I was certified at one time for steel high pressure steam,
 Titanium, and SS. I was also a welding instructor for seven
 years, have read this thread with curiosity,
 and have seen some misinformation, largely based on
 hearsay, and home grown welders.

 To expound on this would perhaps take enough to
 write a book. However, every method has it's place,
 and some systems are quite universal.
 As far as the MIG controversy is concerned, my statement
 that properly executed, MIG or FCAW is capable of
 X-ray quality welds still stands, and anyone well versed
 in this subject would know that.
 Archie

Hi John and Archie,  Well, I am not a certified welder, haven't
learned much from books either, though I certainly have looked.
Strictly the home grown variety, that's me. Nearly every day I MIG
weld thin gage 4130. This is because I tack everything together with
the MIG as a first step in the assembly process.  It is perfect for
this and saves  a ton of time.   Then I subject each and every one of
these tack welds to my home grown x-ray inspection. It is simple and
never allows me to kid myself about the quality of the welds.  To
complete the welds with the torch, I start at the tack and heat it
first.  If the heat radiates outward into the parent material evenly
so that I cannot tell the tack from the parent material, then I have
good penetration and a satisfactory weld. If the tack heats up
quickly and the parent material remains somewhat darker so that I can
easily see the outline of the tack, then the weld is crap.
Unfortunately many of the MIG tack welds fail this test.  The
troubling part is that they all look so good on the surface. All tack
welds with the torch pass this test, as you would suspect.

With check book in hand, I asked the Miller tech rep to come up with
a viable MIG solution for .035  4130 and he said he could not
recommend it for "structural applications".  I don't know if he would
be considered well versed on the subject or not.

I think MIG might be the process of choice for .063  and up tubing.
That stuff is almost idiot proof.   For the thin stuff I need the
ability to instantaneously  vary the heat as the weld progresses.  It
is not there with MIG.  When I see a nicely MIG welded airframe, I
think it looks good "superficially."

Regards,  Jerry

 
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