In Leon McAtee wrote:
Del Rawlins wrote in message
...

To add to Corky's comments, 4130 can be TIG welded with little worry
about the HAZ as well, which is how I am welding the steel components
of my Bearhawk together. I may do some stress relief of critical
clusters and attach points using a rosebud torch,

Seems to be a contradiction here. If TIG works so well why bother
with the "stress relief of critical clusters and attach points"? This
either implies that the welding process is not completely acceptable,
or the rest of the structure has been over built and less than ideal
welds are acceptable. If the later is the case why not use something
like 1026 DOM and forget the post heat alltogether?

No contradiction. I haven't been convinced that stress relief is
necessary, but neither have I been convinced that it hurts anything, and
it only takes all of a few minutes to accomplish. From what I can tell,
even experienced welders can't agree on whether or not it is desirable.

I'm not from Missouri but I still need to be shown that TIG is truly
acceptable for welding 4130.

Over and above 50 odd years of experience in the aerospace industry?
I'm going to say Arkansas, but that's only a guess.

(I have a TIG and could use it, but
don't) I know some certified plane builders do it this way, and have
heard that at least one uses MIG, but to me it seems that heat is
heat, no matter how it is introduced to the metal. From my limited
understanding of metallurgy it's not the quantity of the energy put
into the metal it's the energy density, or peak heat, that is the
determining factor, coupled with the rate of cooling.

Speaking of contradictions, if heat is heat, why do you still need to be
shown that TIG is acceptable for welding 4130?

The HAZ may be
smaller and closer to the weld with TIG but it - is - still there.
Isn't it? Maybe because the TIG HAZ is closer to the weld, and
therefore has a larger area than than the HAZ would have after being
chased out into the tube, one can get a stronger overall stucture by
not post heating a TIG weld?

That's possible, I don't know.

Just to clear up a possible misconception from another poster - I am
NOT suggesting to, or wishing to, substitute ERW DOM mild steel for
4130 in an existing design. I'm well aware of the cascade effect of
changing something on an existing design.

If TIG, or MIG (I'm real good at MIG of thin metal, done lots of it)
welding of 4130 results in an overall better airframe then I'll stick
to 4130. But if there is a substitute, like 1040 DOM, that has a
strength only slightly less than 4130 N, that can be welded with out
any worry of developing a critical HAZ (not 100% sure about this),
then to me that would seem to be a better option for the average
homebuilder.

To play devil's advocate, I would like to be shown instances where
amateur TIG welding of 4130N resulted in homebuilt aircraft falling out
of the sky. Also, before deciding to switch from 4130 to something else
based on price, check out the prices at Dillsburg Aero in Pennsylvania.
Members of the Bearhawk list who live nearby to ACS in California, have
reported that it is still significantly cheaper to have 4130 shipped
from Charlie Vogelsong at Dillsburg than to buy it locally at ACS.

I'm not trying to be argumentative and have no desire to ignite any
flame here. I do like to occasionally challenge the accepted
traditions to see if there might be a "better" way of doing things.
Even if there isn't a better way I, and maybe some others, will get a
better understanding of just why "we do it that way".

Understood. As a relative newcomer to aviation, I get sick and tired of
the deeply held beliefs of many of the mechanics and pilots I encounter,
which often have no basis in reality, or are based on obsolete
information.

----------------------------------------------------
Del Rawlins-
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