WARPING is one of the home craftsman's biggest headaches. After spending considerable time, money and painstaking care in producing a fine piece of furniture, it is disheartening and a keen disappointment to have it later warp and shrink and come apart. But shrinkage and warpage can be held to a minimum by proper conditioning of the wood and by maintaining a close check of its moisture content at the time it is fabricated.

How wood warps: Wood shrinks and warps in definite relation to the direction of the annual rings, and shrinkage is about twice as great when the direction is parallel with the rings as when it is across them. This basic principle is illustrated in Fig. 4. Quartersawed (edge-grain) lumber shrinks the least because the heaviest shrinkage takes place across the narrow dimension of the board. Flat-cut boards have the greatest shrinkage across their wide dimension where it is more noticeable. Also note, Fig. 3, that flat-cut boards tend to cup away from the heart side. This is an important point and should be remembered in joinery.

Detecting warp: Any irregularity caused by warp should be removed because a board that is warped even slightly will continue to twist no matter how it is used. Cut warp, Fig. 8, is detected with a straightedge placed across the board, whereas twist or wind is determined with a pair of winding sticks, Fig. 1, or by placing a straightedge from corner to corner, as shown in Fig. 7. Both methods will reveal two high corners if twist is present, and consequently planing should be done diagonally from high corner to high corner.

Conditioning: conditioning means seasoning the wood to the proper moisture content (M.C.) to correspond with the humidity of its permanent location. The map, Fig. 12, shows proper M.C. for various sections of the country, based on year-round humidity. A variation of 3 percent either way is permissible. Suppose, for example, that you live in a state where the humidity is about 40 percent indoors all year round. Table 1, Fig. 11, shows that the moisture content for furniture under such conditions should be 8 percent. If the wood is 8 percent M.C. to start with, it will be stable and will shrink and expand little even during the cyle of seasonal changes.

Determining M.C.: It is interesting and instructive to make a moisture-content test. Cut a strip about 1/2 in. wide from the center or about 1 ft. from the end of your lumber. Weigh the sample carefully, using a small scale reading grams or grains. Place the sample of wood in the kitchen-stove oven set at 220 deg. F. and weigh it every 20 minutes until it stops losing weight. This will take about 1 1/2 hrs. Then, work out the calculation given in Fig. 11, and you will have the M.C. The amount of shrinkage of a test sample is graphically illustrated in Fig. 10. Although the sample is now bone dry, it won't stay that way. Within three or four hours it will regain approximately half of its lost moisture and size, and in a few weeks will be nearly normal. This verifies the fact that wood is never truly seasoned -- lumber 100 years old will absorb 16 to 18 percent moisture if stored outdoors. The best place to store your wood is in a location where the humidity is about the same as where the finished product will be used. Storing for several weeks in a warm, dry location is a good conditioning treatment.

Surfacing: Warped wood must be surfaced. This job is done on the jointer if the stock is within jointer capacity; otherwise with a planar head, Fig. 14. If the piece is badly twisted, guide runners should be nailed to the edges, Fig. 13, to form a flat base for the work. In using a planar head, be sure to adjust it to take a light cut.

Play it safe: If you have a choice, use edge-grain instead of flat-cut lumber. At least, avoid extreme grain angles in flat-cut stock. Use a wood known to have low shrinkage and good stability. Table No. 2. Woods marked "poor stability" often are suitable if properly conditioned. Be sure your wood is 8 percent M.C. You will note in Table 1 that if wood is 8 percent M.C., the initial shrinkage of a 10-in. board from green wood will be 1/2 in. scant. The board also will be subjected to a seasonal cycle of about 1/16 additional shrinkage and the same amount for expansion. However, you will note that near the end of a humid summer, doors and drawers will swell and bind, and that in the dry indoor air of winter they return to their original M.C. and work smoothly. Some of this normal shrinking and expansion can be stabilized by reinforcing and solidly anchoring the wood in assembly. Thus, if humidity is not excessive, the wood will compress within itself and follow the path of least resistance. However, if you fabricate wood having a 16-percent M.C., the stain of stabilization at 8 percent is just too much, and "pop" go your glue joints and fastenings.

Retarded warping: The end grain of stock roughly cut into turning squares and stored for future use should be given a protective coating of shellac, varnish or oil paint to prevent checking. Lumber salvaged from old furniture and resurfaced on one side only is more apt to warp than if surfaced on both sides, as freshly dressed surfaces invite rapid absorption of moisture. Furniture should be finished as soon as possible after it is completed. Linseed oil, shellac, varnish and other finishes, when applied to the surface of the wood, form a practically airtight covering through which moisture penetrates slowly. Finishing coats retard swelling and shrinkage to the point that if the humidity increases 10 percent for a couple of days, there will be no appreciable change. If your wood is conditioned to 8 percent M.C., it will remain fairly close to 8 percent and you will not be troubled with warping. Ideas in Fig. 15 are worth noting in preventing warping and shrinking. Notice how cupping of a table top is avoided.

Finishing: Finishing often is the prime characteristic in selecting a cabinet wood. When you have a wood that machines and finishes nicely, then you have a top-notch cabinet wood. Information given in Table No. 2 will help in selecting a wood for finish, and is a fair guide as to how the wood should be finished. Finishing is closely related to the natural beauty of the wood, necessitating some knowledge of grain and "figures" for suitable selections. Figures in wood constitute a whole subject in themselves, and the few samples shown in Figs. 10 to 16 can be taken only as typical examples. Perhaps the best way to become acquainted with figures and also the many different kinds of woods is to purchase a set of wood samples, Fig. 6. A set of fifty samples is an inexpensive and worthwhile investment, and it is surprising how quickly identification and general knowledge of various woods can be learned by "leafing" through such a set. The samples are small wood blocks packed in a neat box and should be kept in a clean, dry place.

Grading of wood: A knowledge of wood grading is useful. For example, if you want a popular board for painting, you would order "stained saps," (fifth-grade lumber), and the finished job would be practically as good as if made from "firsts and seconds." Essential grading data is given in Table No. 3. This table is not complete nor absolutely accurate, but it can be taken as a general guide. There are actually ten grades of lumber. Of these, eighth and ninth grade mahogany is the only one of interest to the crafter. This grade comprises wood of firsta and seconds quality but in short lengths. it should be noted in the table that numbered gradings are not comparable between different woods. For example, fifth grade popular is a much better wood for a paint job than fifth grade chestnut. Grading rules for softwoods are much diffeent than for hardwoods, and the differences should be carefully noted from the table.

Article suggested by Matt Ross.