in in different
elements of joined structures._

Illustrations of this are as follows: The grain of the sides of a box
should run continuously around the box, or, in the case of a tall,
slim box, the grain of all the sides should run up and down. In either
case, the grain in the different sides is parallel. In a rubbed joint,
Fig. 269, No. 70, p. 182, to be planed down afterward, in case the
grain is not straight, much trouble in planing may be saved if the
different pieces are laid so that they can all be planed smooth in the
same direction. This may not be possible where the boards are joined
so as to match the grain, as in quartered oak, or where the annual
rings of slash boards are made to alternate in direction so as to
lessen warping, Fig. 280, p. 188.

5. _Where possible, allow for shrinkage without prejudice to
construction._

The most obvious illustration of this principle is panel construction.
In a panel, the frame, which is comparatively narrow, follows the
principal dimensions, and hence does not seriously shrink or swell
itself. But the panel, which is grooved into the frame can shrink or
swell without harm to the general structure.

In a gained joint, as in a case of shelves, Fig. 266, No. 29, p. 179,
the gain in the uprights does not extend quite to the front of the
shelves, and there is a corresponding slight shoulder at the front end
of the shelf, so that if the shelf and support shrink unevenly, no gap
will be apparent.

A drawing-board, Fig. 280, p. 188, is so made that it can shrink or
swell without losing its flatness. Shingles when properly laid, can
shrink or swell without the roof leaking.

6. _Where feasible, undercut joined surfaces so as to give clearance
on the inside and insure a tight appearance. But glued surfaces should
be made to meet flat._

Illustrations of this principle are as follows: The inner end of the
socket in a dovetail joint, Fig. 267, No. 48, p. 180, may be undercut
slightly so as to insure the pin's falling close into place.

The shoulder of any tenon may be undercut so as to allow the edges of
the tenoned piece to close up tight against the mortised piece.

In an end-lap halved joint, Fig. 265, No. 17, p. 178, the edges should
meet all around; if they are to be glued together, they should _not_
be undercut or they will not glue well.

In matched flooring, the underside of the boards is slightly narrower
than the upper side so that the joint may close on the u