"Jim Wilkins" writes:

I just signed up for a blacksmithing class. The instructor isn't
averse to non-traditional methods and has MIG and acetylene in the
shop. What should I watch out for if I plan to hot forge a previously
arc welded joint? I could be welding high and low carbon steels
together.

Normally, you would never plan to forge an arc welded join, at least
not more than just enough to slightly adjust a fit or match to a
drawing.

An exception is tacking pieces together prior to forge welding. If
I don't have a helper and the join is awkward, I might tack two
pieces together with small torch or MIG welds, as little as possible.
In the case of Damascus (properly, pattern-welded) billets tacked at
the ends, you'd normally cut off the weld material before you're done,
not fold it into the finished piece.

Depending on the workpiece and what finish you mean to use, differing
materials -- base and weld filler -- might well show up unsuitably in
the finished piece. In any case, arc/gas wellding tempts you to take
an easy way out rather than figureout a way to exploit the medium.

The central mystique of blacksmithing is that iron is soft, malleable,
mushy, plastic in the smith's hands. As a learner, you should
concentrate on that, abandoning any existing perspective acquired from
welding in the fab shop.

That said, I'm not a purist. When assembling complex pieces that
themselves are expressive of the plasticity of hot iron, arc welding
can make a piece that would be impossible (or nearly so) work well
without intruding the different aesthetic of arc welding on the
aesthetic of a piece. Here's an example:

http://home.tallships.ca/mspencer/crab.html

The legs and claws are attached to the carapace with arc welding,
completely concealed by the snap-on plastron.

This piece,

http://home.tallships.ca/mspencer/ga...destroyer.html

on the other hand, has numerous joins with arc and gas welding. All
those welds were carefully ground, filed and hammered to keep them
from distracting from the overall forged nature of the piece. In this
case there was no other way to get to the desired end.

Oh, and I've been smithing for about 50 years.

--
Mike Spencer Nova Scotia, Canada