A butt joint is a type of woodworking joint. It is the easiest of all joints to make, but is also quite weak. In addition to being used in woodworking, butt joints can be seen in other types of construction where it is necessary to join two structural members, as in welding. People often learn the butt joint first when they start learning about joints, because it is easy to learn and it can be a building block for more complex joinery techniques.
In a butt joint, two pieces of wood are simply butted together. One piece is cut flat, with the end grain meeting the side grain of the other piece of wood. Butt joints can be used to make corners, or to attach pieces of wood at a horizontal midpoint on another piece of wood. In the most basic butt joint, the joint is glued to hold the pieces of wood together, and the joint may be put under tension by the surrounding structural members to keep it in place.
Glue alone is not always enough to reinforce a butt joint. A biscuit or dowel may be used to reinforce the inside of the joint, to ensure that it stays snug. Nails and screws can also be used for attachment, although they will be visible on the end piece. Internal hidden metal fasteners of other types can also be used. If a butt joint is still weak, a small triangular piece known as a gusset may be fastened over the side of the joint to stabilize it and hold it in place.
The big disadvantage to a butt joint is that it is relatively weak. The joint can easily separate under pressure, which can be a problem if it is used on a moving part, as a joint for a container designed to carry something heavy, or in other situations in which the joint may be subjected to stress. The advantage is that it is a joint which can be quickly and efficiently made, which may be beneficial when the desire is to get a project finished. Butt joints can also be used as a form of temporary joinery while a project is underway, and removed later.
Understanding the butt joint also lays the groundwork for learning about other types of joinery. The process of cutting the pieces down and securing the joint familiarizes people with the process of using tools, while the obvious weak points of the joint can become an incentive for learning other, stronger joints which may be more suitable for applications in which the joint will be stressed.