On 30 Aug 2003 11:08 AM, Building The Perfect Beast posted the following:

Done properly, do you feel that there is any difference in the quality
of weld produced by oxy/ace vs. TIG? Is the TIG just less hassle or
what?

Well, many knowledgable and experienced welders believe that the
narrower heat effected zone (HAZ) causes more stresses to be
concentrated right next to the weld, rather than spread out over a wider
area adjacent to the weld. The problem is that while the weld may be
sound, these stress concentrations might cause cracking right next to
the TIG welds. The cure for this is to either weld using oxy-acetylene,
or to post heat the TIG welds using an O/A torch with the "rosebud"
heating attachment, which stress relieves the joint, moving the stresses
away from the more highly loaded weld clusters, and preventing the
cracking. For every welder who holds this opinion, you can probably
find another equally qualified welder (including the guy who helped FAA
revise the welding portion of AC43.13) who believes it to be a non-issue
and the post heating to be unnecessary.

As a mostly self-taught amateur welder, my position is that I don't know
enough to say either way, but that nobody has been able to convince me
there is a downside to post heating the TIG welded joints, other than
the time and cost of the gases used. My plan is to do as Bruce has
suggested in the past, and not worry about it for the most part, but to
also go over some of the more highly stressed critical areas with the
rosebud. Places like the wing and landing gear attach fittings, and the
tailspring and engine mount points.

For the record, I *really* like my TIG unit (a Lincoln square wave 175)
and I feel that the precision, cleanliness, and convenience of the TIG
process outweighs the disadvantages of cost and possible need to strain
relieve welds. But in your case, since you will need to develop oxy/
acetylene skills anyway before you can even think about trying the TIG,
you should just use the O/A torch for your welding since it is easier
and more forgiving. I already had plenty of O/A welding experience
under my belt and I did quite a bit of welding on non-aviation stuff
with the TIG before I ever started putting aircraft parts together with
it.

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Del Rawlins-
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