In this joint the surfaces of the checks are splayed up and down, as shown. If the lower beam is firmly bedded, and the upper beam has a weight upon it, so that the surfaces are kept close together, their splayed form prevents the upper beam from being drawn away in the direction of its length, and greatly strengthens the joint.
Dovetail Halving, see below.
Dovetails are so called from the shape of the pieces cut to fit one another.
They are objectionable in carpentry, because the wood shrinks considerably more across the grain than along it. The consequence is, that as a b (Fig. 164) shrinks more than c d, it is easily drawn partly out, and does not form a firm connection. The joint is, moreover, very weak at the angles w w. This is sometimes improved by cutting shoulders to the dovetail, as at s s in Fig. 165.
Fig. 163. Bevelled Halving.
Fig. 164. Common Dovetail Halving.
Fig. 165. Shouldered Dovetail.
Dovetails are not liable to the first objection mentioned above when the grain in both pieces runs the same way, but in that case, if the timber shrinks, or is strained in the direction of its length, the cheeks are very liable to be split off.
Dovetail Halving (Fig. 164) is a joint in which the dovetail is half the thickness of the piece upon which it is cut, and the notch to receive it half the thickness of the other piece.
See Dovetail Notch, page 66; and Dovetail Tenons, page 70.