On Mon, 26 Jul 2010 00:47:23 -0400, "Steve W."
wrote:

RogerN wrote:
Got my welder out and practiced running some beads on 22Ga sheet then
proceeded to weld the patch panel in place where I cut out the rusted metal.
I had to do a bunch of tack welds until I got it solid, boy that auto
darkening helment is great, first time I ever used one. All these little
tacks and filling in holes with short bursts left me a good bit of weld to
grind. My patch panel didn't match up perfectly at a bend so I tacked the
top and then finish formed the panel in place, it didn't need to be perfect
but did need to be below the surface to be built up with bondo.

After welding and grinding I built up with bondo and inline sanded, built up
with bondo again, inline sanded again, and a couple times again! I had to
weld up a thin place in the metal that showed up when trying to inline sand
the repair flat. The last time I bondo'd I didn't use quite enough hardner
and maybe it will be ready for sanding tomorrow after work. The previous
time I bondo'd it started looking real good, sandpaper made contact with the
whole surface except an angled part I think will take some hand work.

At first I set my welder to feed about 10" of wire in 6 seconds, I saw this
recommended to set 100"/min feed for auto body welding with 0.023" wire. My
preliminary heat setting caused surging, the wire would start an arc, burn
back too far, stop, and repeat. After some trial and error I found out
turning the heat down a little more gave me a more continuous weld.

At first attempt it seems my Century welder should do the job for auto body
welding. After some more practice I would like to go to the Lincoln dealer
and see if they have a Power Mig 140C demonstrator I could try and compare
it to my old Century. I see what you guys mean about the continuous heat
adjustment, I was able to fine tune the heat and wire to run a nice bead,
but the adjustments were tiny.

RogerN



Here is an EASY way to adjust a MIG. First you pick a current level that
you think will work for the steel you have. This isn't real hard and
with some practice you will be able to look at the steel and tell.

Then adjust the wire feed. For this you LISTEN to what the weld sounds
like. What you want to hear is a nice even sound a LOT like frying food
in a pan.

Yes!


As for the rest it sounds like you have most of it figured out BUT I
will tell you that if you didn't put in enough hardener the Bondo will
NEVER set up correctly. I would knock that layer off and mix a new batch.

Me too.


For thin sheet metal you want SHORT tack welds. Nothing longer than
1/2"-1" and not close together. Hit one side then the opposite side. If
you end up with small holes the easy way to fill them is to use a copper
paddle. I make most of mine out of heavy copper sheet. Then just rivet
on a handle or grab tab. Hold the paddle tight behind the hole and use a
motion like a plug weld to fill the hole.

That definitely works. But, with the little Linc SP125+, though I
have certainly blown a few holes, I have never once used a backing
paddle in autobody work. Just turn down the heat a little and weld
the hole shut, rather like doing a rosette weld except there's no
metal behind an eau chitte hole. It's easy with the right machine.