Panel Structures

These include doors and cabinets of all sorts. The principle of panel or cabinet construction is that there shall be a frame composed of narrow members whose grain follows the principal dimensions. In the best construction this frame is mortised and tenoned together and within this frame there is set a thin board or panel which is free to shrink or swell but is prevented from warping by the stiffer frame. The object is to cover an extended surface in such a way that the general dimens

ons and good appearance will not be affected by whatever shrinkage there is. Since the frame itself is made up of narrow pieces, there is but little shrinkage in them. That shrinkage is all that affects the size of the whole structure, because wood does not shrink longitudinally to any appreciable extent. The shrinking or swelling of the panel does not affect the general size. The cross construction of the frame also prevents warping, since, in the best construction every joint is mortised and tenoned. The panel may simply be fastened on the back of the frame, but a better construction is to insert it in a groove made in the inside of the frame in which the panel is to lie and have free play. The panel may be made of one board or of matched boards, may be plain or have raised or carved surfaces, or be of glass; and the joints between frame and panel may be embellished with moldings mitered in, but the principle is the same in all cases.

The frame of a door, Fig. 288, illustrates the panel construction. The upright, outside pieces are called the "stiles," the horizontal pieces the "rails." There are also the "top-rail," the "bottom-rail," the "lock-rail" (where the door-knob and lock are inserted), and sometimes the "frieze-rail" between the lock rail and the top rail. The "muntin" is the upright between the two stiles.

The joint commonly used is the haunched or relished mortise-and-tenon, Fig. 267. The tenon is sometimes doubled, Fig. 288, and a fillet (f) may be inserted to cover the ends of the tenons, or the joint may be a blind mortise-and-tenon, Fig. 266, or in cheap construction, dowels may be used. The best doors are now made with cores of pine covered on the visible sides with heavy veneer. Large surfaces are covered by increasing the number of parts rather than their size, as in wainscoting.

Picture-frames also belong in this class of structures, the glass taking the place of the panel. They are made with mortise-and-tenon joints, Fig. 266, slip joints, Fig. 267, dowelled butt joints, Fig. 264, end lap joints, Fig. 265, No. and, far more commonly, mitered joints, Fig. 268. Mitered joints are the easiest to make, for the joints can be cut in a miter-box, Fig. 181, and glued in a picture-frame-vise, Fig. 172. This joint needs reinforcement by nails, Fig. 268, by dowels, or by splines. If the sides are of different widths, the fitting of the joint is more difficult. Mitered joints are the only kind suitable for molded frames. The rabbets are cut out with a rabbeting-plane before mitering and assembling.

The principle disadvantage of a mitered joint is that, if the wood shrinks at all, it opens at the inside corners, as in Fig. 289, because wood shrinks sidewise but not lengthwise.

In window sashes, the dovetail joint, Fig. 267, is the common one at the upper end of the lower sash and the lower end of the upper sash, and the mortise-and-tenon joint modified is used at the lower end of the lower and upper end of the upper sash. The glass takes the place of the panel. In blind sashes, the pinned mortise-and-tenon joint, Fig. 267, is commonly used.

In all these cases, the constructed panels may be treated as separate boards and joined together with dowel pins or splines or dadoed together without any other framework, tho the corners are often reinforced by cleats or blocks glued into them. Sometimes, however, as in chests, Fig. 290, posts are used instead of stiles, and rails are mortised or doweled into them and the panels set into grooves in both posts and rails. In this case the bottom is raised from the floor, and may be dadoed into the bottom rails, or dowelled into them or even supported by strips attached along their lower inside edges. The chest really is a union of both paneled and framed structures.