Handwork in Wood by William Noyes
A tusk tenon or shoulder tenon
The keyed mortise-and-tenon is made as in a thru mortise-and-tenon, except that before cutting the tenons the holes for wedges should be laid out thus: measuring from the shoulder of the tenon, locate by superposition or measurement the outside of the mortised member. Deduct from this 1/16" and square a fine pencil-line across the face and opposite side. This line will be the inside of the hole for the wedge, and the 1/16" is deducted to make sure that the key wedges against the mortised member. On the upper surface of the tenon, lay off toward the end the width of the wedge at this point, A B, Fig. 252, and square across. On the under surface, lay off the width of the wedge at this point, C D, and square across.
[Illustration: Fig. 252. Keyed Mortise-and-Tenon Joint.]
Gage the sides of the wedge hole on both upper and lower surfaces of the tenon. After cutting the mortise and tenon, bore and chisel out the hole for the wedge, taking care to cut the side toward the end on a bevel to fit the wedge.
_No. 40. A tusk tenon or shoulder tenon_, Fig. 267, is
_No. 41. A double mortise-and-tenon_, Fig. 267, consists of two tenons side by side in one piece fitting into two corresponding mortises. It is used in joinery, as in door-frames, but not in carpentry.
_No. 42. A haunched mortise-and-tenon_, Fig. 267, is made by cutting away part of the tenon so that that part of it will be much shorter than the rest. The haunch gives the tenon great lateral strength and saves cutting so large a mortise hole. It is used in panel construction, as where the rails are joined to the stiles of doors.
First plow the groove in all the members. This should be of the same width as the thickness of the tenons, which is ordinarily one-third of the thickness of the frame. The groove is approximately as deep as it is wide. Lay out and cut the tenon the width of the entire piece, minus, of course, the depth of the groove. The mortise should not come too near the end, or the portion of wood outside it will shear out. Hence the tenon is narrowed on the outside enough to insure strength in the mortised piece. The rule is that the tenon should be one-half the width of the rail, minus the groove. But enough of the tenon is left full width to fill up the groove at the outer end of the mortised piece. This is called the _haunch_. The width of the mortise is equal to the width of the groove, its length to the width of the tenon. Before assembling the panel frame, put soap or tallow on the corners of the panel to prevent its being glued to the frame.