Got a question for the real welders from an old farm boy who owns a welding machine and pretends to weld sometimes.
It was time for a new exhaust system on my GMC Suburban, so I purchased the parts including two catalytic convertors, 4 O2 sensors, new muffler, and new tailpipe. The original system was welded together at the factory, and had to be cut into two pieces to get it out. The new system went back in fine, except that the tailpipe and muffler had a joint which needed to be clamped or welded.
To convince myself that I could weld the pipe with my 100A Sears MIG using flux core, I took the old piece that I'd cut apart with a sawzall and welded it back together (Butt weld). The pipe thickness was about 1/16" (.065) so I figured that I'd need about 3/4 of the 100 amp welders capacity. Now the Sears welder doesn't have amperage settings, so I set it to 3/4 of full voltage and a wire speed of ~1/2 of full speed. This has worked well in the past, and in fact worked beautifully on the old pipe. I got a beautiful flat weld with full penetration, and no holes.
Piece of cake, so far. BTW, no shielding gas, just flux core wire.
The new tailpipe slipped over a smaller pipe at the output of the muffler, and they fit tightly, so I hit it with the flapper disk to remove the anti-corrosion coating and started welding. This time I couldn't get the weld to lay down flat at all, and ended up with an ugly (but functional) bead. At least it sealed the pipe, but I wouldn't want to show it to anyone. In fact, I'm tempted to grind it down and re-weld it even though its under the truck and real awkward to get to.
I'm thinking that the second weld didn't have enough current, but I don't want to blow through the thin pipe and compound my problems. The first weld was a butt weld, and the second weld was an overlapping seam.
What did I do wrong?