Butt joints are the simplest, most basic type of joints. It’s simply two pieces of wood joined, held by glue and reinforced by screws.
How Wood Joins
In butt joints the end of one piece of wood joins the end of the other. There’s nothing more than that. The sheer simplicity of this also makes it the weakest of all type of wood joints.
Joining the Wood
Glue needs to be applied to the end of the piece of wood that joins to the side of the other piece. To have the wood remain it place it needs to be secured using nails or screws, with screws giving a firmer join.
In order to have a god join between the pieces of wood, both must be straight, particularly the end that will be joined to the side of the second piece. That way the maximum possible area of wood comes in contact with the second piece. A miter joint can be a butt joint and offers more strength.
Butt joints can prove useful for joining pieces of wood but they need to be sparingly used and only in situations where the strength of the joint isn’t vital. Even with screws they’re not strong and won't always hold.