Sheet metal is frequently used in all levels of construction, be it residential, public or commercial. The most effective way to permanently join two pieces of metal together is to weld them. When welding sheet metal, it is important to understand the major types of joints that are available. Five major types of joints are used to join sheet metal: butt, corner, edge, lap and T-joints.
Butt joints are the most straightforward type of sheet metal joints. The two sides of the joint are simply placed side-by-side, and the welding torch is run along the seam in between them.
Corner joints are used to join to pieces of sheet metal at a 90-degree angle to one another. The two joint sides are put together so that they make an "L" shape, and then welded together.
Edge joints are one of the weaker types of sheet metal joints. The two sides are joined together so that they lie in the same plane, and the welding torch is run along the very edge, so that the sheets are only joined along the small edges of their side. Because this can be such a precarious joint, the metal sheets joined with an edge joint must a ¼-inch thick or less and cannot be used to carry a lot of weight.
A lap joint involves placing one piece of sheet metal over another, "lapping" it. Lap joints are among the strongest joints available. They work best when the two pieces of metal are overlapped at least three times the thickness of the thinnest piece of metal being joined.
T-joints are very similar to corner joints; once again, the two pieces are joined together perpendicular to one another. However, whereas corner joints join the two pieces together to form an "L" shape, T-joints join them together to form a shape like the letter "T."