Paragraph 70. The keyed mortise and tenon joint is a very old one. It was formerly used only in heavy construction work or where great strength was required. In recent years, however, it has found its way into a great many kinds of cabinet construction, where it is used for its artistic effect as well as for strength. There is no joint which will present greater strength than the keyed mortise and tenon. If it is properly proportioned it will withstand almost any kind of strain and cannot be torn apart until the material is split and almost absolutely destroyed. In the keyed mortise (B) and tenon (A) construction the laying out and execution are very similar to the through mortise and tenon, except that the tenon is cut very much longer so as to extend a sufficient distance to have a mortise cut in it and allow a key (C) to be used.

Lay out the mortise and the tenon as explained in Paragraph 66. Allow the tenon to extend through the mortise far enough to receive the mortise for the key and still leave sufficient wood to give the necessary strength. In designing the keyed mortise and tenon joint it is necessary to take into consideration how much strength will be required. In cabinet and artistic work of course strength is not an important point. Then one must consider the general appearance of the work. It is quite common to see rather heavy keyed tenons on a piece of work which is not subjected to a great strain, but because of the massive appearance which is desired throughout the work large tenons and keys are used. This is a matter of judgment and no definite rule can be given. Note: In cutting the mortise for the key and in preparing the key, be sure that the key tightens in such a way as to hold the two pieces of material closely together. The key must not tighten laterally or it will split the end of the tenon. It is well for the key to fit rather loosely this way, but to bind very snugly in the other direction. The size and shape of the key is a matter of taste. The key is sometimes cut in a scrolled or artistic form.

Figure 55.