This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Another way of strengthening a mitered joint is by inserting what are known as "keys" into the pieces on the outside of the joint. These keys are thin slices of hard wood which are placed in slots prepared to receive them and held in place by means of glue. As the glue fastens them securely to each of the pieces at the joint, they hold them firmly together and prevent the joint from opening. Fig. 79 shows a joint of this kind. The keys, of course, show on the outside of the joint, but they can be cut very thin and only the edge of them can be seen. The keys give a great amount of additional strength to the connection and are more effective than is a spline for preventing the joint from opening, as they come right out to the edge of both pieces and can be placed as near together as seems to be necessary. Sometimes, instead of being placed horizontally, or in a plane perpendicular to the edge of the joint, they are inclined as shown in Fig. 80. This arrangement strengthens the joint still more. Tenon Joint with Haunch. In Fig. 81 is shown a form of joint called the "tenon joint," with the addition of a "haunch" which adds considerably to its strength. This joint is used extensively in the making of doors. One of the pieces to be joined is rabbeted on each side to about one-third of its depth, leaving a projecting part called the "tenon" about one-third the thickness of the piece. This tenon is then rabbeted on either the top or the bottom, but instead of being cut entirely back to the body of the piece, the rabbet is stopped a little short of this and a "haunch" is left. In Fig. 81, A is the tenon and B is the haunch. The other of the two pieces which are to be joined is cut with mortises to receive the tenon and the haunch in the first piece. Fig. 81 shows the simplest form of simple tenon joint, but there are many variations of this, two of which are shown in Figs. 82 and 83. Fig. 82 shows a single tenon joint with two tenons, while Fig. 83 shows a double tenon joint which has four tenons. Both of these joints have haunches as well as tenons. The one most commonly used is that shown in Fig. 82.
Fig. 77. Rabbeted Miter Joint.
Fig. 78 Rabbeted Mitered-and- Splined Joint.
Fig. 79. Mitered Joint Keyed Square.
Fig. 80. Mitered Joint Keyed Diagonally.
All of the splices so far considered have been end to end splices, that is, they have been those kinds which would be used in fastening pieces together at the ends. It often becomes necessary, however, to fasten pieces together side by side. Any of the methods already described for splices will be applicable in such a case, but there are in addition a few others which are especially useful, two or three of which will &8226;now be described.
Fig. 81. Tenon Joint with Haunch.
Fig. 82. Single Tenon Joint with Two Tenons.
Fig. 83. Double Tenon Joint with Four Tenons.