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In addition to the angle of the gun inline with the weld, we should look at the angle of the gun in the other plane-this is called the work angle. For some work, the gun will be angled more toward one side of the joint, but for a butt weld, the best gun angle is 90 degrees. In the case of a lap joint, a 60- or 70-degree angle is preferred, and with a T-joint, a 45-degree angle is used. These angles may sound odd at first, but once you start welding joints, you will quickly see why different joint configurations require different gun angles.

If you are just learning MIG welding, practice on metal around 1/8-inch thickness until you start to get the feel of the process. Once you feel confident welding 1/8-inch material, you can then move on to samples that are thinner and thicker. Auto body sheetmetal takes a good deal of control to weld properly, since you are trying to get as flat a bead as possible, while achieving full penetration and avoiding burn-through. It certainly can be done, and the more you practice, the easier it gets. Another consideration with sheetmetal is that the shrinking caused by welding will often cause distortion, and the flatter the panel, the more distortion you get. For this reason, it's a good idea to skip around when MIG welding sheetmetal, welding perhaps 1/2-inch in one location, and then moving a foot or so away to make the next small weld, and to let the metal cool completely before you add more weld to your first passes. While this slows the process a bit, you'll find that skipping around and keeping the heat buildup down greatly reduces the amount of distortion you get.