Essentials of woodworking

by Ira Samuel Griffith

—Probably no joint has a greater variety of applications than the blind mortise-and-tenon, [Fig. 162]. It is of equal importance to carpentry, joinery and cabinet-making. The tenon shown has four shoulders; it is often made with but three or two.

93. Directions for Tenon.

—(1) Measure from the end of the piece the length of tenon, (see also directions for tenon, [Section 89]) and mark with the point of a knife. (2) Square knife lines entirely around the four sides at this point to locate the shoulders. (3) Lay the rule across the face edge near the end of the piece and mark points with the end of the knife to indicate the thickness of the tenon, [Fig. 159]. (4) With the head of the gage against the face side, set the spur of the gage in one of these marks, then fasten the set screw, [Fig. 160]. Gage on the end and the two edges as far back as the knife lines. When there are several tenons remember to mark all of them before resetting. (5) Set the gage in the other mark, the head of the gage being placed against the face side; then gage as before. (6) In a similar manner, place the rule across the face side, mark points with the knife for the width of tenon, set the gage to these points, and gage on the face and side opposite as far as the shoulder lines and across the end. The head of the gage must be held against the face edge for both settings. (7) Rip to all of the gage lines first, then crosscut to the shoulder lines, using back-saw. (8) The end of the tenon may be slightly beveled that it may be started into the mortise without tearing off the arrises of the opening.

94. Directions for Laying out Mortise.

—(1) From one end of the piece measure the required distance to the nearer and the farther ends of the mortise. Mark points with the knife. (2) Square lines across at these points. (3) Lay the rule across the face into which the mortise is to be cut and mark points with the knife for the sides of the mortise. (4) Set the gage as was done for the tenon, the spur being placed in the knife point mark and the head of the gage being pushed up against the face. Gage between the cross lines. (5) Reset from the same face for the other side of the mortise, and then gage.

If a mortise or tenon is to be placed in the middle of a piece, find the middle of the piece, [Fig. 3], [Chapter I], [Section 1], and with the knife, place points to each side of the center mark at a distance equal to one half the thickness or width of the tenon or mortise. When several mortises or tenons of the same size are to be laid out and are to be equally distant from a face, the gage needs to be set but twice for all—once to mark the nearer edges and once for the farther edges of the tenon or mortise. Should there be several like members with like joints, the gage settings obtained from the first piece will suffice for all.

The importance of working from face sides or face edges only, cannot be overestimated. To work from either of the other two sides of a piece would make the joints subject to any variation in the widths or thicknesses of the pieces. To gage from the faces only, insures mortises and tenons of exact size no matter how much the pieces may vary in widths or thicknesses.

95. Directions for Cutting Mortise.

—Two methods of cutting mortises are in common use, (a) boring and chiseling, and (b) chiseling alone. First method: (1) Fasten the piece in the vise in a horizontal position. (2) Bore a series of connecting holes to the required depth, [Chapter IV], [Section 45], with a bit slightly smaller than the width of the mortise. (3) The sides of the mortise are next pared to the gage and knife lines, beginning at the auger holes and working with thin slices toward the lines. This method requires care and patience in order to get the sides of the mortise cut square to the surface. It is especially well adapted to large mortises from which much wood is to be removed.