Interlocking Chair Joint


A joint designed with a view to strengthening the construction of chairs at the point where they are weakest is shown in . The joint is an interlocking one so arranged that, once the chair is glued up, no motion of the side rail can be possible. The groove in the side rail tenon is cut in such a manner that, on the insertion of the back rail tenon, the joint actually draws up and, having done so, is locked in position. The exact location of this groove is obtained in a similar manner to
that used in marking out tenons for drawbore pinning, i.e., the tenon is inserted in its mortise and the position of the back rail mortise transferred to it, after which the lines are set back by 1⁄64 in. (approximately) to cause the joint to draw.

From the illustration the construction of the joint should be clear. The method is particularly adapted to a section of rectangular form where one side is longer than the other, such as the back leg of a chair, as this shape allows for the accommodation of the extra length of tenon required.