Building in Wood
Perhaps it was the icy wind blowing through gaps in the first wooden door one cold winter night that caught the attention of its builders, and forced them to notice that the wood had shrunk away from its frame since they had built it.
Whatever it was, a plank of wood sawn from a tree still poses the same problem for today's builders. It will shrink as it dries out after being freshly cut from the tree--but that's not the end of its misbehavior.
Even when dried, the plank will continue to swell in size and shrink back again in response to the changing humidity, all through the seasons, year in and year out, forever. Unfortunately for our ancient door builders, its length will never change, only its width and thickness; in other words, all of the change in size is perpendicular to the grain, not parallel with the grain. (See "Wood" for more about wood's properties.)
This causes stresses and strains which make building with wood more difficult than with many other materials. A door that is three feet wide in the summer might lose an inch of width by the time winter winds come seeking out the cracks and crevices.
Eventually, someone had the idea to build a separate frame of wood around the perimeter of the door. If the grain of the wood in the frame was always aligned with the outer edges of the door, then the frame itself would not shrink in any direction. The original door, or panel, could be mounted inside the frame, and the panel could shrink or swell as much as it liked without affecting the size of the frame.
In this way a door could be built which would fit throughout the seasons. Today nearly all doors are some form of frame-and-panel construction, as are many cabinet and furniture doors and cases. The reason is the unvarying size, or dimensional stability, of such a door.
But the grain of wood is also the characteristic that contributes to its strength, so it makes sense to use this to advantage. Wood is stronger along the length of the grain than it is across the grain. Although most people couldn't break a broom handle accross their knee, if the grain of the wood was perpendicular to the length of the handle, it could be easily snapped in two.
The frame we just invented for our hypothetical door is therefore not only dimensionally stable but strong as well. All of the wood in its outer frame is parallel to the frame members; it is what we call long grain.
But how do we join the frame together?
Joinery evolved as man's attempt to do what nature had already done in the original tree: attach one piece of wood to another with strength and permanence. Since we can't grow it together, as does the tree, we have to rely on cutting wood into interlocking shapes, or on gluing wood together...or both.
Joinery can be divided in two general types of construction: frame and case.
Frame construction can be thought of as joining one stick to another. Doors, windows, and tables are all examples of frames, as well as most wood-frame houses.
Case construction involves the joining of one panel to another; it is distinguished from frame construction in that the pieces to be joined are wider. Cases are essentially boxes: cabinets, drawers, desks, chests and armoires are examples.
I will show some of the joints used in furniture and cabinetry construction in the next sections.
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