Fig. 85 - Lap Dovetail.
Any joint which is formed by a piece of wood being shaped with a dovetail is said to be dovetailed, for this form of construction is found in many instances where perhaps it might not be regarded as such by the novice. From its peculiar formation it is specially adapted to resist lateral pressure. Thus it is much used in fastening the top bearers or pieces which connect ends of carcase work afterwards covered over, as in the case of cabinets, sideboards, etc.
In this case the lap dovetail is used, the stretchers being sunk in the ends and level with their edges. When small, as in the case of pedestal writing-tables, the tops are solid, that is, covered in entirely; but if of any considerable size, these dovetailed tops, or rather top bearers, are formed of two pieces of wood of any convenient width, and generally of pine. The front bearer is faced or veneered on its front edge to match the outer wood. In order to give additional hold on the ends, these bearers are generally widened out by gluing triangular pieces to them, so that there is an open octagonal space, generally oblong, between the back and front bearers.
Fig. 86 - Formation of Mitre-cap Dovetails.
The construction and arrangement will be understood from Fig. 87, which shows them fitted within the ends.
In addition to glue, a few nails are often used, driven through from the top into the ends to secure the bearers. If the nails are driven in a slanting direction it is impossible for the bearers to be pulled up, so that the joint is quite firm.
Bearers under drawers may also be dovetailed, but when connecting ends in this fashion, the piece of wood into which the bearer is dovetailed being both above and below, the conditions are somewhat altered, and dovetails made as any already described would not answer. Instead, the dovetail must be reversed, and be formed from the edge of the wood, as shown in Fig. 88. In situations such as supposed, the dovetailing may be on both surfaces, but usually it is only formed on one, the lower, as Fig. 89. In order to prevent the dovetail showing through on the face edge of the end, and to give the bearer a square shoulder, it is usually cut back for a short distance, as in Fig. 90, and the corresponding socket stopped at a similar distance from the front edge of the end. Such a dovetailed bearer is knocked in from behind. This form is stronger, inasmuch as it binds the ends together, than the mortise and tenon or dowelled joint, one or other of which is more commonly used, and is sufficiently strong for ordinary purposes.
Fig. 87 - Dovetailed Top-bearers.
Fig. 88 - Dovetail or End.
Fig. 89 - Dovetail, One End.
Mitred corners are often seen, but they are never used where strength is essential unless supported in some way, either by blocking inside, as in plinths, which will be found mentioned more fully elsewhere, or by keying. This is a common method for small fancy boxes, as it is strong enough for such work, and is expeditious. The edges to be joined are shot to a mitre, glued, and then further strengthened by strips of veneer, let in as follows: - Saw cuts, a fine saw being used, are made from the corners, not parallel with the top and bottom, but inclined up or down; a small piece of veneer, fitting tightly, is glued and forced in. The edge, not the end, of the veneer should be at the bottom of the cut, so that the grain is transverse. When the glue has set the veneer is trimmed off level with the surface. Such a joint appears as shown in Fig. 91, and will, no doubt, be recognised by many readers. The number of veneer keys depends on the size of the work.
In framing, for doors, etc, other kinds of joints are necessary, those most commonly used being the mortise and tenon or the dowel, though much is done by simply halving the pieces.
The mortised and tenoned joint is much used for all kinds of purposes, and either it or its substitute, the dowelled joint, is constantly coming into requisition. In its simplest form it is shown in Fig. 92. The tongue on A is the tenon, which fits closely within the mortise or opening in B.
Fig. 90 - Dovetail Stopped Back from Front.
Fig. 91 - Mitred and Keyed Corner.
To make such a joint - and, with natural modifications, all mortises and tenons are made in the same way - set the mortise gauge so that its points mark the width of the mortise and thickness of tenon, which may be about one-third of the thickness of the edge. Run it along top and bottom edge as far as necessary, and over the end of both pieces, working from the face sides, i.e., keeping the block of the stop on the front. Now, with the square mark off - using a sharp edge, marking point, or chisel, not pencil - from each end a little more than the width of the corresponding piece, on edges and sides. These marks give the length of tenon and depth of mortise from the end. It then only remains to saw away the waste pieces, but unless this is done carefully the mortise and tenon will not fit tightly on account of the saw kerf. To allow for this saw on the outside of the tenon leaving the gauged marks just on its edge, and when cutting the mortise saw inside the lines. When properly managed, the parts ought to fit each other accurately, without paring with the chisel. The mortise may be chopped out with a chisel, working from both edges as in the case of dovetails. Much cutting is often saved by boring away the waste wood with a bit, and then using the chisel to square the sides and corners. This is especially the case when the mortise is a large one.