A butt joint is made when two pieces of wood are butted together and glued. When you glue an end-grain surface of one board to another wood surface, the joint won't hold unless it's reinforced with dowel pins or some other reinforcement. When you use the butt joint to glue two or more boards side by side, or edge grain to edge grain as when making a wide top for a table, however, the joint can be quite strong. You must make sure that the joining edges are planed smooth to form a perfect fit, though, and that the joint is glued and clamped sufficiently.
Miter Joint-
The miter joint is formed by cutting corresponding angles, usually 45 degrees, on the ends of two pieces of wood and joining them together. The most common use of the miter joint in furniture is in mirror and picture frames. The miter joint may be reinforced with pins or dowels or with the installation of a wooden back panel, often 1/4-inch plywood.
Dado Joint-
A dado is a groove cut across the grain of a piece of wood. A dado joint is formed by cutting a dado in one piece of wood the exact size as the square-cut edge of another piece. The square-cut edge of the second piece is then inserted into the groove of the first piece to form a tight, secure joint. Dado joints are commonly used to join wood at right angles, as in bookcase shelves. Sometimes the dado is hidden because the groove is not cut all the way across the board to the front of the bookcase. This kind of dado joint is called a blind dado.
