Elements of woodwork

by Charles A. King

Fig. 22.—Permanent Lumber Ways.

16. To minimize the warping of lumber.—(A.) Do not place lumber piles less than one foot apart, as it is necessary that there should be a continuous circulation of air through the pile in all directions. (See b, Fig. 22.)

(B.) Lumber piles are usually four feet in width, and should be built up with sticks of that length, which are placed between the courses of boards. It is important that these be placed directly over each other and the ways; otherwise there will be short kinks in the boards, as shown at c. It is such carelessness as this that causes a great deal of loss. In piling very expensive lumber, the front sticks should be laid so as to project a little over the course of boards below, and the boards of the course above should project the same distance over the stick, in order to give the front of the pile an inclination to the front, as shown at d, which will allow most of the rain-water to drop clear of the boards below, instead of running down the front and finding its way into the pile.

(C.) Square piles are sometimes built, but in these the boards should be laid with large spaces between them, to allow perfect circulation of air. It is obvious that in a pile of this sort, the boards in the center of the pile will not come in contact with the air as much as those on the outside, and that consequently, unless carefully piled, the boards may be damaged by the moisture souring instead of drying out, which usually results in decay.

(D.) During the drying out process, all boards change their form more or less, depending upon the shape of the tree trunk, the kind and quality of the wood, the part of the tree from which the log was cut, as well as its size and age, the relation of the annual rings and medullary rays to the surfaces of the board, the length of time since the log was cut before being made into lumber, whether it had lain in water for several months, and the method of piling. Thus it will be seen that in every stage of preparing lumber for market, a high degree of skill and judgment is necessary to insure the best results.

Fig. 23.—Warping of
Lumber.

The greatest deterioration in lumber, after it has been cut and properly piled, is generally due to the tendency to warp, the cause of which is indicated in Fig. 23, and which may to great extent be minimized by skillful piling. If this sketch is studied carefully, it will be noticed that the middle board is thicker in the middle than it is at the edges, and that the curves of its top and bottom sides are practically uniform. This is because the annual layers are at nearly a right angle with the sides of the board, which causes the board to shrink in thickness, and very little in width. This is due to the tendency of lumber shrink around, or parallel with, the annual layers. This tendency also causes the star shakes, as at c, Fig. 3, which is because the inner layers of the log, being less than the outside layers in circumference, and less exposed to the dry air, do not shrink so fast nor so much. This tendency is again illustrated in Fig. 23, in which it will be seen that because the outer annual layers shrink faster, they cause the outside of the board, or the part which grew toward the outside of the tree, to become narrower, and to assume a concave shape, while the side nearer the center of the tree, or the inside of the board, becomes convex. This is also the reason why boards cut near the outside of the log will shrink in width more than those cut nearer the center, which shrink in thickness proportionately more than in width.

(E.) For the purpose of taking advantage of the tendency to warp, and applying it to its own remedy, boards should be piled with the side which grew nearer the center of the tree uppermost. This will help to correct the tendency of the board to warp, as explained above, as the side which would naturally assume the concave shape will be underneath, and less likely to warp than if it were uppermost. This is not generally observed in stacking common lumber, since it needs care and judgment to do it properly, but it should be done if valuable lumber is being handled.