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Mortise and Tenon Joints

Construction How-To, Finish Carpentry, Furniture, furniture, Outdoor Furniture, Woodworking - Directory April 3, 2003 Sonia


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Mortise and tenon joints are some of the oldest woodworking joints. Many classic 18th century furniture pieces such as the Philadelphia Chippendale highboys, Sheraton desks and others feature these joints. Mortise and tenon, if properly constructed, can also be some of the strongest joints. They can be used for outside frames of cabinets and chests, inside drawer-support frames, for table legs and chair parts as well as other projects.

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A mortise is basically a slot cut in a piece of stock. A tenon is a reduced tongue on the end of the stock that is cut to fit into the mortise. Several different types of mortise and tenon joints can be constructed. An open-end mortise joint has the mortise all the way through the stock, allowing the end of the mortise to be exposed. This joint is often used to connect rails to posts or legs. Running the tenon entirely through the stock and then cutting a mortise in the end of the tenon, allows the tenon to be pinned in place with a small wooden dowel or tapered stick. With the latter, a sturdy joint is created that can be tightened by driving the tapered stick further inward. The open-end mortise joint disassembles quite easily by knocking the pin out and removing the tenon. The hole for the pin should be offset just a bit on the crosspiece to provide a tightening action between the two pieces. This joint is quite common in early American and other casual styles of furniture.

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Another form of open-end joint is the corner mortise and tenon. The corner joint is commonly used for frame and panel sections such as raised-panel cabinet doors, or panel frames on chests.

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A blind mortise-and-tenon joint has the end of the tenon concealed. The mortise does not go all the way through the stock. This joint is also used for rails and posts.

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The tenons may be shaped in different styles as well. A straight tenon only has two cut sides. The opening of the mortise side is revealed. A shouldered tenon has all four sides of the stock reduced to conceal the mortise. By cutting a step in the tenon you create a haunched tenon that provides a good, strong joint used for frame construction. A bare-faced mortise and tenon has one edge exposed, normally on the inside of the piece.

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As with many traditional joints, mortise and tenon joints can be cut using hand tools or with a variety of power tools. The tenon can be cut with a hand saw, a radial arm saw or table saw, or with a dado blade in either of the latter. The mortise can be cut by using a chisel, or by first drilling holes into or through the stock, then finishing the mortise with a sharp chisel.

Creating Mortise and Tenon Joints With Hand Tools

Creating mortise and tenon joints with hand tools requires quality, sharp tools. You1ll need a good square, marking gauge, brace and bit, mortise chisel, corner chisel and a smooth-cut backsaw. The chisels, butt gauge and saw shown are from Woodcraft Supply, makers of fine woodworking tools.

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Tenons can be cut with hand tools. The first step is to mark the tenon with a square and marking gauge.

Position the stock in which the mortise will be cut facing upward, or the side in which the mortise is to be cut facing upward, in a vise or work-piece holder.

Place the stock that will have the tenon across it, with the end flush with one side of the mortise piece. Use a square to make sure the tenon piece is square with the mortise piece. Mark both sides of the tenon stock on the mortise stock. These are the mortise shoulder lines. If more than one piece is to be mortised, mark them all at this time.

If the tenon is to be shouldered to conceal the mortise, use a square to mark the width of the shoulders back from the first marks. These are the mortise-limit lines.

Determine the thickness of the tenon. This will also be the width of the mortise cut and is usually one-third the width of the tenon stock. It’s a good idea to keep the cut a size that can be cut easily with an available mortise chisel or brace and bit. Mortise chisels commonly run 1/4, 5/16, 3/8 and 1/2 inch. For 3/4-inch stock, a 1/4-inch wide tenon would be appropriate. Use a marking gauge to mark the thickness of the mortise to hold the tenon. Either a very sharp pencil or knife should be used to create a fine line mark. Then mark the waste or area to be cut.