Butt Welding 18 Gage w/MIG?

Wow, all great input,

I'm using a Lincoln 140C MIG w/mixed gas. The gas pressure is set at about 18-20. The dials are infinite adjusting and are set to 2 for speed & E.5 for temp. I'm getting good color on the back side so I don't think the issue is heat but I agree it may be gap. I was having trouble bridging across the gap when I had it at 3/16 so I dropped it down to 1/8 (changed cutoff wheels in my angle grinder). I realized that the bigger gap was going to allow me better depth but I kept missing the edge of the metal and shooting the wire past the hole! That's why I thought the copper backer might me a good way to go???

I'll look through the tutorials and give it another whirl.
Thanks again...dartlover

PS: Anybody who knows how to weld live in my neck of the woods, Phoenix Az?