Runner

frame around the panel provides a lightweight construction unit that remains stable in length as the panel inside shrinks and expands in its groove. (See AW «31, for more on frame-and-panel doors.) Familiar uses include doors, cabinets, lecterns, desk sides, drawer bottoms, headboards, and similar large pieces, but the concept extends further. A mullioned window is a frame with glass panels. A table is a frame with the panel laid on top.

There are various ways you can Fix

the panel in or on its frame. Finning a door panel at the middle will keep it centered while allowing its width to expand and contract. To hold a table-top in place, screw it tightly to the frame at the center, then set the screws at each side in slots. Or you can use the familiar metal or wood "buttons" set in a groove. (See Fig. 4.) To keep a round tabletop flat, use screw-on cleats, and slot the end screw holes so the top can move.

Mortise-and-Tenon Problems

A mortise-and-tenon joint is pure cross-grain construction. But if you construct these joints carefully, as shown in Fig. 3, they should resist wood movement. (See AW «18, for more on mortise-and-tenon joints.)

As I write this article, my computer sits on a cherry tavern table made with mortise-and-tenon joinery before 1750. It has no value as an antique because previous owners cut the aprons for knee room and replaced the original top at least once. But when I bought it at a roadside stand 20 years ago it was solid as a rock, because it had spent recent years in a shed, at a similar moisture content to the day it was made. After a winter of drying indoors, it began to creak a little, but it still stands firm. As far as I can tell, there's no glue in the joints now. The table's pinned tenons were made according to the principles shown in Fig. 3. Had it been merely glued, it would have fallen apart generations ago.

Case Construction

Dovetail carcasc construction allows sides, top and bottom to move in tandem. But when you add cross-grain runners for drawers or apply moldings to the sides of a cabinet, the parts don't all move in the same direction. Resulting tensions have been known to crack case sides and pop off moldings.

Craftsmen have created numerous solutions to allow the back ends of case moldings to move. (See Fig. 5.) In the simplest, the mitered front end is glued and fixed firmly to the case, while the unglued back end is tacked on with wire brads. The brads in the molding flex as the case side moves. More sophisticated solutions fix the back end with a screw from inside the case (with the screw hole slotted) or allow the back part of the molding to ride on a short runner. The runner can be as simple as a screw head that fits a routed slot on the molding.

You can use similar approaches with crown moldings—secure the miter against cracking by gluing it, but attach the rest of the molding with brads or slotted screws. Drawer runners are handled in the same way— tight fronts, loose backs.

The ancient way to fix the bottom to a chest so it can move is to nail it. We gasp at tills perfidy, but nails are more sophisticated than they look. A nail will enlarge its hole at the point where the bottom and case sides meet, allowing movement, while the point of the nail remains relatively fixed and secure. Rustic old-timers often nailed tabletops for the same reason. City cabinetmakers scorned nails, however, and set their chests on frame-type bases, which is still the current practice. (See Fig. 5.)

Miters, Dowels, and Screws

As shown in Fig. 6, moisture plagues miter joints. The miter is half end grain in the first place and presents a mediocre gluing surface. If that weren't bad enough, when the frame pieces expand or contract in width, the angle of the miter changes, and few frames can resist the tension. The wider the molding, the

FIG. 5: CASE CONSTRUCTION

Front of molding

Screw rides in slot in case side, allowing movement

Back part of molding rides loosely on

Back with brads that flex to allow movement

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