The common Dovetail has already been described in Part I.
The Mitred or Secret Dovetail is chiefly used by cabinetmakers for highly-finished drawers and boxes, when for the sake of appearance it is desirable that the dovetails should not be visible. In this joint not much more than half the thickness of the boards is dovetailed, the outer portion (s t, Fig. 153) being mitred as shown, so that the dovetails may not show on the sides of the exterior angle.
In order, further, that the dovetails may not be visible upon the upper surface of the boards to be united, the top of the joint is mitred right through the thickness of the board, a c, for a short depth (from a to b). This may also be done on the lower surface if that is likely to be seen. Fig. 153 shows only one of the boards to form the angle, but the construction of the other will be readily understood, as it is cut to fit into the projections and indentations of the one shown. The spaces between x x x in the figures are the sockets, the corresponding projections on the opposite board being called the pins This joint is not so strong as the common dovetail.
The Lap Dovetail is a joint in which the pins on one board, B, do not extend entirely through the thickness of the board A, but are concealed by a portion of the board which is not cut through. In this case, of course, the pins of the board A only are visible.
This joint is well adapted for the fronts of drawers. The piece, A, which forms the front shows no dovetails, while B forms the side in which their appearance is of no consequence, as it is not seen except when the drawer is open. Keys. - When plain surfaces of boarding of considerable extent are required, as in dados, window backs, wall linings, etc., the boards are generally ploughed and tongued and joined with glue.
Tapering pieces of wood called "keys," very well seasoned, are often let into a wide dovetailed groove across the back, as shown in Fig. 155.
These keys keep the surface of the boards in the same plane, and allow the work to shrink and expand according to the weather. The edges of boards to be united are sometimes rebated at the back of the joint, and strips of wood are glued in, so as to keep the edges close together. Boards so secured must be very well seasoned, or they will split.
Double Dovetail Keys are small pieces of hard wood, of double dovetail shape, let in, with the grain, across the joint to be secured.
When a heavy circular-headed frame consists of several curved pieces, the parts are often kept together by keys of hard wood, of the shape shown at H K in Fig. 156, glued in.
If the pieces are very wide, a cross tongue, t, is put in on each side of the key, and the joint is tightened up by wedges, w w.
Screw bolts may be substituted for the keys, the cross tongue still being used.