Some great advice so far. Only things I would add.
1. You have to be moving when you start, and always keep moving esp. with
sheet metal. About the time you stop to think "gee this is looking good" you
will burn through. Once you burn through stop, move someplace cool. Starting
again in metal that is hot is almost impossible for someone without much
experience.
2. Make sure things are clean. Paint, oils, rust make it almost impossible
to weld sheet metal. (spoken from an amateurs point of view, I know the
wizards out there can do almost anything) You have to crank the heat so high
to burn through the crap that the underlieing metal doesn't have a chance.
Besides you WILL contaminate the weld if there is stuff there.
2a. Make sure your metals are mated well. Use lap welds if possible. butt
welds in sheetmetal are really hard to do well. ANy gaps wider than the width
of the wire are hard to fill. Use a weld through primer. watch for edges and
corners, less of a problem with AC welding, but you can still get slightly
freaky effects at corners.
2b. Once you have made a mess, go back, grind off the wiskers, crap, carbon,
etc. Clean things up before trying again. Many times you will compound your
errors by trying to go back.
3. Use a fine wire. The finer the wire, the faster you can feed it at a
lower amperage and the less heat you produce. Problem is that the fit has to
be better, and you can have a great looking weld with no penetration that is
holding nothing.
4. Push the metal around a bit on sheet metal once you get started. I weave,
others do little circles, others stitch, this keeps the heat spread out a bit
and seems to make me a bit steadier. You want to see the base metal melting
and mixing with the weld metal. This is harder to see on sheet metal but easy
to see on steel plate so start with that. The first time I heard this I
thought the guy was putting me on but you can see it once you know what you
are looking for. See number 1.
5. Keep your tip clean. If you are arcing off the edge of the tip/shield,
you end up with inconsistent heat at the wire. This can happen without being
able to really see it. Look for the tell tale burning and marks arount the
edge of the tip.
Last suggestion is to take an evening welding course. It's fun, you get to
use up someone elses welding supplies, try a variety of welding techniques
(mig, TIG, DC, AC), you get to see what really good equipment can do, and you
have someone there that can teach you. Barring that, start welding on just a
piece of metal with no joint. Write your name, go back and forth, paly
around. Then move to a joint. Once you get the coordination you can go
easier. Last use a good welding helmet and strong lights. For an amateur
(me) this was the best thing I could have done. You can see the weld start,
and you can see where you are going. Many times I have started three inches
from where I want to be because I couldn't see and moved my hand when the
helmet dropped. If you have the mask you hold in your hand get a new one.
Very few can weld one handed.
John
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