Mortise and Tenon Joints
Tips and information on how to make a mortise and tenon joint for woodworking.
The diagrams given below illustrate the method of forming joints known as the mortise and tenon. This is a joint in common use, being required in the construction of almost every important article of household furniture. Certain articles, such as chairs, may have no other class of joint used in their formation.
In preparing for mortise and tenon joint, first true up both the pieces of wood, indicated at A and B, dressing them to within a shaving or two of their finished thickness; and then, with the mortise gauge, set to the thickness of the tenon and its distance from the face of the pieces, mark the end of the tenon-piece and the side of the piece to be mortised; and then with the try square cross-line both, as indicated by the dotted lines, defining the length of the mortise in the one case and the length of the tenon in the other. The thickness of the tenon will vary according to circumstances, but, as a rule, in ordinary joinery, it is equal to one-third of the thickness of the material on which it is formed. To cut the tenon, fix the piece A in the bench-vise, vertically, and carefully saw down with the grain, with the tenon saw, to form the sides of the tenon. Finish each side-cut accurately at the cross-lines, and remove the piece from the vise and saw on the cross-lines, removing the two side pieces.
At this stage, the end of the piece assumes the shape indicated at A. The mortise is usually sunk by means of a mortise-chisel, a trifle less in width than the width of the mortise : this is applied so as to cut across the grain or fibres of the wood, and is driven into the wood with a mallet. The sides and ends of the mortise are finally trued and cleaned with broad and narrow firmer-chisels.
Should the amateur not be provided with a proper mortise chisel, he can readily form the mortise in the manner shown in the drawing below. That is, after he has gauged and cross-lined the wood, he can bore, with a Jennings twist bit, a series of holes as closely together as practicable, as indicated at A, and of the required depth. When this is done, the rest of the wood can be easily removed with firmer-chisels, and the mortise finished to receive the tenon. It is highly probable that this easy and expeditious method of mortising will be generally adopted by amateurs who have not had experience in the use of the mortise-chisel and mallet.
When the mortise has been formed, the tenon should be inserted and the condition of the joint examined, and tested in all directions with the try-square. If it does not fit closely or squarely, the tenon must be withdrawn and any necessary paring executed with a firmer-chisel. When satisfactory, both the mortise and tenon must be well coated with hot glue and the joint hammered or clamped tight and true. The surplus glue should be wiped off with a rag or sponge dipped in hot water, and the joint allowed to dry.
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