Metal is a fundamental element of building due to its strength and durability. The best way to attach two pieces of metal to each other, especially if building a permanent structure, is to weld the two pieces. There are many ways in which to attach the two pieces, and it is a good idea to become familiar with the different types of metal joints and their uses before beginning work on a metal-joining project.
The simplest and most widely used metal joint is the butt joint. It is most commonly used for tanks, pipes and pressure vessels because a butt joint allows for a flat surface. To make a butt joint, simply place two pieces of metal end to end, so that they are laying on the same plane, and weld along the seam between them.
T-joints are another extremely common type of metal joint. They are made by joining one piece of metal with another at a 90-degree angle, making a shape that resembles the letter "T." T-joints are most often used in construction of machinery and structural steel. T-joints are extremely strong; however, when using T-joints it is important to remember that the weld must be placed on the side of the joint upon which pressure will be applied.
Corner joints are another popular and effective form of metal joint. Corner joints come in two types. Open corner joints are made when the end of one of the joints meets with the end of another joint, creating a space where the thickness of the two ends is visible. The space left between the two sides must be filled in with filler metal. Closed corner joints, on the other hand, have the edge on one end flush with the edge of the other, with no space between them.
Lap joints consist of one piece of metal lapped over the other. Lap joints are among the strongest joints possible in welding. Usually, the metal must overlap about three times the thickness of the least-thick element of the joint. Lap joints are commonly used in spot welding and torch brazing.
Edge joints are also a popular and useful form of metal joint. The two pieces lay back to back, so that their edges are flush, and the welder connects them together along their flush edges. Edge joints are not particularly strong and are best if used only in metals that are not weight bearing. For this reason, they are often used in sheet metal welding.