_No. 37. A dovetail mortise-and-tenon_, Fig. 266, is a thru mortise-and-tenon beveled on one side so as to form half a dovetail. The corresponding side of the mortise is also beveled and made wide enough so that when the tenon is pressed well up against its beveled side a wedge may be driven into the space left on the straight side. It is used to tenon a beam into a post especially where the post is fixed against a wall. It is also used in machinery frames which are made of wood.
_No. 38. A pinned mortise-and-tenon_, Fig. 267, is one in which a pin is driven thru holes bored thru the mortised beam and thru the tenon to keep them from drawing apart. It is used in heavy framing as in bridges, in wagon-making, in window-sash, etc.
_No. 39. A keyed mortise-and-tenon_, Fig. 267, is one in which the tenon protrudes thru the mortise far enough to receive a removable key and thus be drawn up tight to the mortised member. It is used in work-benches and in ornamental joints like knock-down bookcases and in other mission furniture.
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 one in which the tenon proper is quite thin but is reinforced by a thicker shoulder called a "tusk." The upper shoulder is beveled. The object of this form is to weaken the mortised member as little as possible but at the same time to increase the strength of the tenon. It is used in joining tail beams to headers in floor framing.