Quote:
Originally Posted by Tom Wesenberg
I bought my Lincoln SP-125 MIG welder about 20 years ago with the idea to use it for doing body repairs on my Model A's, such as rust patches, or fender crack repair. A few years ago either Flop, Brent, or Kevin mentioned that MIG produces a hard weld. I used my MIG to repair a cast iron generator pulley with a piece missing. I thought I would file the weld to shape, but the file wouldn't even scratch the weld, so I had to use my Dremel with a grinding wheel. That's when I found out just how hard the MIG weld is.
I'm thinking such a hard weld wouldn't be good for repairing a fender crack because it would probably be so hard it would crack again quite easily. When I repaired the missing metal in the log splitter cover I decided to gas weld it, and that worked fine. So, for Model A fender patch work or crack repair, is TIG or is gas welding the preferred way to go? Or are they equal in weld quality and durability? Thanks
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The order from soft to hard is Oxyacetylene first, TIG second, and MIG third. The way to have the best weld is to fuze weld it where there is little filler rod used. This is a very strong weld. Remember it is not just good enough to grind the weld, ...the weld needs to be planished too so as to eliminate any stresses caused by the heat-induced shrinkage.
FWIW, a TIG-welded panel can still be planished well, but a MIG weld cannot. Ironically, we have used MIG wire as a filler rod with a TIG torch, so the hardening process is created by the type of welder and not the welding wire.