No. 29. A gain joint is a dado which runs only partly across one member, X. In order to make the edges of both members flush and to conceal the blind end of the gain, the corner of the other member, Y, is correspondingly notched out. In book shelves a gain gives a better appearance than a dado.
Fig. 266-29 Gain
A gain joint is laid out in the same way as the dado, except that the lines are not carried clear across the face of X, and only one edge is squared and gaged to the required depth. Knife grooves are made in the waste for starting the saw as in the dado. Before sawing, the blind end of the gain is to be chiseled out for a little space so as to give play for the back-saw in cutting down to the required depth. To avoid sawing too deep at the blind end, the sawing and chiseling out of waste may be carried on alternately, a little at a time, till the required depth is reached. It is easy to measure the depth of the cut by means of a small nail projecting the proper amount from a trial stick, Fig. 251. The use of the router, Fig. 122, [p. 83], facilitates the cutting, and insures an even depth.
Fig. 251. Depth-gage for Dado.
MORTISE-AND-TENON JOINTS
The tenon in its simplest form is made by dividing the end of a piece of wood into three parts and cutting out rectangular pieces on both sides of the part left in the middle. The mortise is the rectangular hole cut to receive the tenon and is made slightly deeper than the tenon is long. The sides of the tenon and of the mortise are called "cheeks" and the "shoulders" of the tenon are the parts abutting against the mortised piece.