In a dovetail dado, Fig. 266, No. [28], [p. 179], it is usually sufficient to make the dovetail on one side only.
Many very elaborately spliced joints have been devised, which have no practical advantage over the simple ones, Fig. 264, Nos. [4]-7, [p. 177].
A butt joint, Fig. 264, No. [11], is stronger than a mitered joint, Fig. 268, No. [52], in a box, for the latter is almost sure to shrink apart. Where appearance is important, a ledge and miter joint has the advantage of both, Fig. 268, No. [58].
8. Keep a due proportion of strength between the fastenings (joints) and the pieces fastened: i. e., the construction should neither be frail on the one hand, because the pieces of wood are weakened by too much cutting, nor clumsy, on the other hand, because then the fastenings would be inordinately strong. In other words, the different parts should be equally strong.
Illustrations of this principle are as follows: In a fished joint, Fig. 264, No. [2], the plate should be attached so as to reinforce the splice at the weakest point.
In a scarf joint, Fig. 264, Nos. [5] and [7], the angle should be oblique enough to give the greatest leverage.
In a tusk tenon, Fig. 267, No. [40], the tenon is made but one-sixth the thickness of the timber, whereas the tusk is made much larger.
Where a mortise is to be cut in a timber bearing weight, it should be cut in the neutral axis, where the cutting of fibres will weaken it least.
In the mortise-and-tenon of a table-rail, Fig. 267, No. [43], there should be a wide shoulder above the tenon of the rail so that the top of the leg above the mortise will not shear out. The mortise should be as near the outside of the leg as possible so that the inner corner of the leg may remain strong. The tenon should be strong enough to share the strain with the shoulders.