The two pieces that were put together in your last lesson can be pulled apart in one direction. The piece A, Fig. 47, can be drawn out from B towards the right, but the part of B which projects above A in the figure prevents the tenon from being removed by a pull upward, or in the direction of the arrow. If we wished, however, to get rid of the projecting piece above the tenon, so as to have a smooth corner, we should lose this advantage, and unless the tenon were narrowed, A would not be able to resist either a force toward the right or an upward force, but would yield in either direction. If we wish, in this case, to have A held fast so that there shall be one direction in which it can be pulled without being withdrawn, we must give the joint another shape. This shape is called the "dove-tail," from its resemblance to the spreading tail of a dove, Fig. 48. It is evident that if the dove-tailed piece A is fitted into a hole of the same shape, it cannot be withdrawn by pulling in the direction of the arrow. With this explanation you will now be able to understand the sketches in Fig. 49, in which A and B represent the plan and elevation of the mortise-piece, C and D those of the tenon-piece, and E and F those of the two pieces put together.

Fig. 47.

The two pieces are to be first carefully planed true and smooth as in the last exercise. The work is then to be laid out. The thickness of A B (1 1/2") is to be marked with a sharp pencil on C D, first on the upper side shown at C, then, by means of the square, on the front side D, and then, from these two sides, with the square, on the other two sides. In the same manner, the thickness of C D is to be marked, first on the right-hand face of A B, then on the front face shown at B, and then from these on the other two. Next the two inclined lines marking out the dove-tail are to be drawn on the upper face of C, then on the lower face, and then their ends are to be joined by lines drawn across the end of the piece. Lastly, similar inclined lines are to be drawn on the end of A, and from their extremities lines are to be drawn down the right and left faces of A B to the crossmark. Mark with a cross x, as in Fig. 54, to prevent mistakes, the pieces of wood that are to be cut away, and before beginning to cut, put the pieces together and make sure that your marks are right. The lines are all to be drawn with a very sharp pencil, so that if you cut exactly up to the center of each line, but not beyond, the dove-tail or tenon and the hollow or mortise shall fit perfectly together.

Fig.48.

Exercise 30. End Dove-Tail

Fig. 49.

Page 113, Fig. 49. - The last part of this figure should be changed to appear as below:

The cutting of the marked portions from the tenon-piece C is very simple. It is all done with the back-saw, and if the tool is handled with skill, nothing will remain for the chisel. To do this, however, would require more skill than you can be expected to possess as yet, and you may therefore cut not quite up to the marks with the saw, leaving a little wood to be trimmed off with the chisel. Be very careful, when trimming this off, to have your chisel as keen as possible, and to use the sliding movement already described.

In removing the wood from the mortise-piece also, the first part of the work is done with the saw. Hold the piece upright in the vise, place the saw just within the inclined marks on the end of A, but very near them, and cut down to the cross-mark. In making these cuts on A, as well as the corresponding cuts on C, and any others which go lengthwise of the grain, be careful not to hold the saw quite horizontally, or with the tip inclining downward, as in cross-cutting, but with the handle downward as in ripping, as in Fig. 50. Otherwise the teeth will stick too firmly in the wood, and the saw will jump, or "chatter." In making cross-cuts, as the two short cuts in C, this precaution is not necessary.

Fig. 50.

When the two saw-cuts in the mortise-piece have been made, the next operation is to cut out the piece of wood between them down to the cross-mark. Here, as in the last exercise, the work of cutting with the chisel may be lessened by the use of the brace and bit; but we will, for the sake of variety in exercise, use a different method, cutting the mortise with the chisel alone. Lay the piece on the bench, with the dove-tail end from you and the right side (Fig. 49, B) up: this is the side on which the two cuts come nearest together (1 1/8"). Set the edge of your one-inch chisel at the dotted line, Fig. 51, about 1/8" inside of G H, the flat side of the chisel being towards you. Strike a smart blow with the mallet, driving the chisel in about a quarter of an inch. Do not strike a series of feeble, uncertain blows, but one vigorous one. You may, if you choose, after placing the chisel, give it one gentle tap to make sure of starting it right (though this is not necessary), but when you are sure that it is right, strike it boldly. Having driven the chisel in about a quarter of an inch, you have now compressed the wood so that it is difficult to penetrate any farther. Set the chisel about a quarter of an inch nearer to the end, but tipped forward, as at b in the Figure, so that it shall work towards the cut you have already made. It will thus throw out the little triangular chip shown in the Figure. Set the chisel upright again at the same point as at first, and drive it in farther. Move it nearer to the end, tipped forward again, and cut out another chip. Advance thus, till you have got half-way through the piece; then turn it over and proceed in the same way from the other side. Be careful not to let the chisel go through and strike the bench. If you cannot check it, place a piece of clean board under your work. As the piece to be cut out is wider on the second face than on the first, you must incline your chisel right and left, so as to cut under a little while working from the first face and to avoid cutting into the sides of the mortise when working from the second.

Fig. 51.

When the piece is cut out, the three sides of the mortise are to be carefully pared so that the tenon will go in, fitting closely, but not so tightly as to split the mortise-piece.