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

Your "home grown" X-ray test, while invalid in welding standards,
has merit, and is not a bad way to verify the weld fusion.
Some of the higher end MIG machines have fade controls and start
current timers to alleviate your heat adjustment as the weld progresses.
And of course, like any additional bells and whistles, dig in
for additional $$$$.
Archie

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org