Posted by chriscase on Friday, August 03, 2007 at 20:29:24 :
Something I learned from Verne, the old welder. He had a piece of copper about 1"x 4" x 3/16" that he could clamp behind joints on thinner stuff. Then he could crank up the amps, and get full penetration in one pass, from one side. He protected that piece of copper like his life depended on it. It was the one tool he wouldn't loan.
Seems copper soaks up so much heat that mere steel weld heat won't melt into it. So after welding, the copper will just fall off. It works with aluminum too, but it just needs a bigger piece. So whenever possible, I use aluminum to back up butt joints in sheet metal.
Butt, when using that technique to fill a spot that rusted/sandbasted through, I used a 3x4 piece of .090 on my fender. It flexed nicely to match the curve of the front lip. Cool, I squirted a bunch of wire in there. Unclamped, the aluminum did not fall off. Or go flying with a love tap from my hammer. so I flipped it over, and saw stalagmites hanging off. I had burned through the heat sink, and welded to it too. I dunno what alloy I made, but it did go away with some grinding- and no bigger hole to patch after welding up a mere pin hole either.
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