Tom,
A little add-on since, as noted, you're never going to get away from the
occasional blowthrough.
Tip #1 -- Blowing a hole is like falling skiing. The longer you wait
to accept the obvious, the worse the consequences. When you see the sag
start, the color change, even the sound change....stop! You'll still likely
have a hole by the time you get your finger off the trigger, but it'll be alot
more manageable.
Tip #2 -- Fixing a manageable hole is the easiest thing in MIG
welding, if you set it up right. Try this, it's very fast because it requires
virtually no waiting. Tim noted that pulling away from the surface slightly
will create a little ball. This can be very useful, though you want the ball
on the surface rather than on the wire end. Turn your welder down one (or two
if necessary) heat settings. Put the gun down on the surface, 30-45^ to
vertical with enough wire out that it touches the surface about a 16th to a
very short 3/32nd from the edge (more if very thin). Tap the trigger (about
the duration of "1" in counting a second as "one-thousand", or a hair less).
You now should have a little glob next to the edge. Do this all the way
around the hole (NOT in sequence -- dot around) until there are no gaps. By
the time you're done, it will look like a mess, ugly and there may be a fair
amount of that brown oxidation byproduct around. Ignore it if you want since
it's about to get consumed and the penetration of the little globs is slight
at best, don't resist wire brushes too well. Go back to normal heat. Start a
bead with the gun straight down at some point in the ring you've made. Follow
the ring around at a hand speed that just melts the ring onto (not into) the
surface metal. When you close the ring, immediately increase your hand speed
and spiral around in a circle closing inwards. Stop as SOON as you see the
middle of the hole disappear.
This is functionally the same as Tim's method, heat is absorbed by the
melting blobs, which then provide support on cooling as you move further, but
it's very fast. I don't even bother putting the visor down for the blobs
part, just look away each time since the gun is braced on the metal, and I
usually stop briefly after completing the blob ring to let things cool, just
to be antiwarp safe. But after a little practice (very little, this really is
a fast learning curve), if you don't bother to wait, you can do a hole start
to finish in 20-30 sec. !! And it will look good and be clean solid and
almost flat metal.
Chris Hill
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