butt head, butt weld.., I need some help Options

[TravisNeff]

Hey all,

I have been trying to patch up A/C holes in my tub and having a helluva time blowing holes in the metal and voids around the weld area. I start with tacks in the corners and start tacking around the world in an offset pattern, when I have about 12 tacks in a circle I try to join the tacs. However when I tac, I most always blow a hole in the new sheet metal, or in the old panel. I have the worst time in the vertical position. I have ground down both sides of the panel (and patch) to clean metal. If I am not blowing a hole, only about 50% of the weld gets good penetration, when I hit it a little longer I blow a hole. I have even used a sorta chill bar to back the joint (1" copper pipe squished flat with a bend, suggested by another lister). Also, I am making most of my holes just buzzing a tack, not so much once I have an arc established.

I have a Millermatic 175, using .023 wire and Argon/CO2 (about 24lbs pressure when I hit the switch), Guide states I should use #2 on voltage and 50 on the wire feed speed. I have no problems welding lap joints at these settings and it sounds like bacon frying when it does it, so I know I am close.

I have gone down to 1.5 on voltage and reduced the wire feed to 40, still no luck. I have expanded my stickout (experimenting with 1" plus down to the 3/8's I normally do). The welds suck. Once I get done and grind the welds down smooth I almost always find a crack/void where the metal joins the weld. Weld, grind, weld grind. I can eventually get it right, fixing each one of the patches once I grind it down. I have tried the butt weld clamps, but the gap is huge, I can get the metal to almost (or actually touch) and hold it in with a magnet.

What am I missing? Should I be using metal ready to clean the metal even further, try another technique? I am holding the gun at an upward angle and a touch over to the side (hell I have tried just about everything).