Fig. 15.
Fig. 16.
When a log is sawed into boards or planks (Fig. 16) the middle board shrinks but little in width and in thickness at the centre, but becomes thinner towards the edges. It does not curl, because it is cut through the centre of the log and has no more tendency to curl one way than the other. The outside board shrinks least in thickness and most in width, and all, except the middle one, shrink differently on one side from the other. They become convex toward the pith, or heart, and concave toward the outside. Different kinds of wood shrink and warp to different degrees. You can learn something about these matters by examining the stock in any lumber-yard.
Now to come to the practical application of our brief study of the log and the sawing process: if you merely wish to get the most that you can from a log in the form of boards or plank, have the pieces sliced off in the simple way just shown (Fig. 17). This is the usual way of sawing for ordinary purposes. Boarding for the outside of a house, for instance, cut in this way answers every purpose. By this process the central boards will be good and the outer ones inferior,[10] as just shown (Fig. 16), but for common work all can generally be used.
Fig. 17.
Fig. 18.
