Before you can make anything successfully, you must have not merely wood, but the right kind of wood for the purpose. There are, also, "choice cuts" in lumber, as the butcher says of meat, and judicious selection of the stock often makes all the difference between a good job and a poor one; so let us examine a log and follow it through the sawmill.

You have, of course, seen the rings, or circular lines, on the ends of pieces of wood (Fig. 9). These are called the annual rings,1 and each ring marks a new layer of wood added to the tree, for, as perhaps you may have learned, the trees we use for wood-working grow by adding new layers of wood on the- outside. Examine the ends of pieces of wood of various kinds. In some pieces these rings will be very plain. In others they will be quite indistinct.

Notice that the wood nearest the bark, known as the sap-wood, usually looks different from the inner wood, which is called the heart (Fig. 9).

In some trees you will see rays, or lines, radiating from the centre, and known as the medullary rays (Figs. 9 and

1o), because they spring from the pith (Latin medulla).

Fig. 9.

1 So called because in the common trees of temperate climes one layer is added each year.

Sometimes these lines are too fine to be noticed.

You will see from Fig. 1o that the layers of wood are also shown in the lines of what we call the "grain " on the surface of a piece of wood cut lengthways, and that the lines of the grain are continuations of the annual rings. You will also notice at the ends of timber, after the seasoning has begun, cracks radiating from the centre, showing the natural lines of cleavage or separation.

Fig. io.

Fig. ii.

The way the log is sawed is important, though you might naturally think that the only thing is to saw it any way that will give pieces of the required size and shape.

Why is green wood heavier and softer than dry wood, and the sapwood of green timber softer than the heart? Because of the sap or water contained. The amount of water is sometimes even as much as fifty per cent, of the weight of the wood, but the quantity depends upon the kind of tree, the season, etc. Now the more water the green log contains, the more it will shrink. It begins to dry and shrink as soon as the tree has been cut down. The sap-wood shrinks more than the heart because it contains more water, and faster because, being on the outside, it is more exposed. The log shrinks most in the line of the annual rings, that is, around the tree. It shrinks much less in the line of the medullary rays, that is, across the tree. Shrinkage lengthways is too slight to be considered ' (Fig. 11).

The result of all this unequal shrinking is that the log tends to split,orcrack open, at the circumference (Fig. 12), the cracks running in toward the centre, in the line of the medullary rays. If the log is halved or quartered, so that the inner parts are exposed, the drying goes on more uniformly throughout, the cracking is not so bad. and the parts of the log will shrink somewhat as shown in Figs. 13 and 14.

The beams, joists, planks, or boards cut from a log have the same tendency to shrink unevenly that is found in the log itself. This causes them to be irregular in shape and to curl or warp more or less, according to the part of the log from which they are taken. A piece cut from the centre of a log will thus hold its shape better than if cut from one side

(Fig- 15).

Fig. 12.

Fig. 13.

1 Although the shrinkage lengthways is not usually noticeable as affecting the length of a board, it shows slightly by its effect in causing the pieces to spring, or become bowed lengthwise, as you will see in many boards which have been left free to spring while seasoning.

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.

Fig. 14.

Fig. 15.

Fig. 16.

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 thepiecessliced 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,1 as just shown (Fig. 16), but for common work all can generally be used.

If you wish the highly figured grain2 often seen in oak, ash, chestnut, etc., you can get it by sawing the log as just shown in Fig. 17. The figure of the grain will be most marked in the outer boards (Fig. 18), because the annual rings are cut more obliquely in them than in the boards at or near the centre. These boards (Fig. 17) will tend to change their shape, as just shown (Fig. 19), but if they are to be firmly fastened in some way, or confined (as in a panel), handsome grain effects can be obtained.

Fig. 17.

Fig. 18.

Fig. 19.

1 In addition to the curling, the outer boards will be poorer because they contain a greater proportion of sapwood, which is usually inferior to the heart-wood.

2 By this is not meant the figure or flashes shown by the medullary rays, or "silver grain," seen in quartered oak and some other woods, but the figure of the grain without the medullary rays, as seen in plain oak, etc.