The most common joint for custom picture framing is the mitered joint. It consists of two pieces of wood with ends cut exactly at a 45-degree angle. These pieces are joined with a thin bead of glue, two dowel rods, two screws placed in the backside of the joint at a sharp incline or via a variety of cut grooves. These grooves and splines remain at 90-degree angles but slide into each other and are hidden by the 45-degree angle of the joint.
These interlocking joints also make use of grooves and splines. In dovetails, the splines are shaped to look like slightly angled bird's tails or a dove's tail feathers. They require precise cuts and extra work, but add a unique look to any custom frame. Resistant to lateral pulling force, these joints slide into place with relative ease. Properly fitted dovetail joints lock into place with no need for extra screws, dowels or glue.
One of the oldest joints, mortise and tenon joints connect at a ninety degree angle. They form a strong connect via a simple mortise hole and tenon extension. The tenon slides into the mortise and both are hidden by the joint. A small layer of glue is applied to both surfaces to help secure the joint together. Two small wooden wedges hammered between the mortise and tenon or two small pin nails are also used to secure mortise and tenon joints.
These joints make use of grooves and splices on a simple 90-degree angle. The resulting frame looks like a butt joint from head on, but at the sides the splices are easy to see. Bridle joints add stability and strength to the ninety degree angle, while also being simpler to produce than mitered joints. Bridle joints are secured with a small amount of glue or pin nails hammered into the back of the frame.
The simplest and weakest of joints, this butt joint is one end piece pressed against the side piece at a 90-degree angle. No angles. No special interlocking grooves. A butt joint is usually glued together, but can be reinforced with a couple of long nails hammered in from the opposite side of the side piece. It can also be reinforced by inserting two dowel rods between the end and side pieces or adding a reinforcing strip of wood diagonally between the two pieces of the butt joint.