Material. - The joint of Exercise 11, and a piece of hard wood, 3/4" square and about 5" long. Work. - To fasten the tenon in the mortise with a pin.

Bore with a 5/8" auger-bit, through the face of the piece and mortise, 1" below the face-edge, as shown in Fig. 1. The line a is marked by pencil and rule, and the point b marked in the middle of this line for starting the point of the bit. The hole is not bored all the way, but when the point shows through, as at a, Fig. 2, turn the piece around and bore from that side to complete the hole. By this means a clean cut is made on both sides of the piece. Test the auger-bit with the try-square, to keep it straight until fairly started into the wood.

Place the tenon in the mortise and mark the center of the hole on it with the point of the bit. Remove the tenon, and start the bit about 1/16" nearer the shoulder. The hole thus bored (Fig. 3) is not in a line with that of the mortise, as shown at a, Fig. 4, but when the pin is forced through, the pieces are brought closer together, forming a stiffer and stronger joint.

The pin is planed to 5/8" square, chamfered with plane or chisel to an octagonal shape, rounded and pointed with the chisel, as shown in Fig. 5, which is just one half size. In practice, the pin is driven in flush with the face of the mortise-piece, the protruding portion being either allowed to remain, or sawed off close.

For large through mortise-joints, such as are seen in the heavy frames of barns and mills, two oak pins are used, as at a, Fig. 6. Sometimes the pins are intended to act like wedges and force the parts together, as shown at b, Fig. 6. This joint is common in machine-frames.

Formerly, when pins were used to a greater extent, they were compressed by being forced through a tapering hole in an iron block. This had the effect of binding the pin firmly in the joint.

Fig. 7 is an example of a double mortise, and is used for securing the central leg of a table to the top. It is sometimes made without the shoulders a, a, which is bad practice, because they give greater stability to the joint.

Ex. 12.

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7