A "Dovetail" is a tenon or pin, made in the shape of a truncated wedge, the outer end being the wider, as shown in Figs. 204-206. Such a tenon, when fitted into a mortise or groove of corresponding shape, obviously cannot be drawn out without shearing the wood, hence a dovetail joint is very strong, irrespective of glue or nails. Dovetailing, however, is seldom used in joining standing finish, being confined principally to fittings, cabinet work and furniture. Still there are places in other kinds of work where the dovetail makes the best joint and should be used in preference to other joints.
Fig. 205 shows the common dovetail joint for external angles. This is the strongest joint, but is not used in cabinet work, except where the pin ends showing on the face can be covered with a moulding.
The joint shown in Fig. 206 is called a lapped dovetail, because the front laps over the ends of the pins so that they do not show on the face. This makes nearly as strong a joint as the common dovetail, and is largely used in uniting the front and sides of drawers.
For highly finished drawers and boxes the mitre or secret dovetail, shown in Fig. 207, is sometimes used by cabinet makers. Only one of the boards to form the angle is shown in detail, the other being made to fit the projections and indentations of the one shown. When put together this joint has the appearance of a mitre joint, but as the dovetails have only one-half as much holding surface, it is only about half as strong as the lapped dovetail, and the latter is to be preferred for large drawers. Dovetailed joints in joinery are always glued.
Glued and Blocked Joint. - Many joints in joinery and cabinet work are made by gluing the connecting parts together, and also gluing blocks of wood into the re-entering angle, as in Fig. 208, to further strengthen the joint and preserve the shape of the angle. Such work is said to be "blocked and glued," and as long as the glue holds it makes a strong joint.
For all sorts of curved surfaces small blocks are glued together and then covered with a veneer, or sometimes the wood is bent to the form required and blocks are glued on to the back to keep it so.
Glue is also used by itself to connect the edges of boards in making one wide board, and when the grain of the wood is carefully matched the joint can hardly be detected. If the boards are thoroughly dry and a good quality of glue is used, the joint will be as strong as the solid wood.
Glued joints, however, sometimes come apart through continual changes in temperature and humidity, or because the wood was not thoroughly dry, so that it is always best to strengthen the joints by dowels, or by a tongue and groove.
Glue is very extensively used in the best grade of joinery and in cabinet work, but it is best not to depend upon it entirely, except in the case of veneers, etc.