Fig. 63. The Forest, Norway Spruce, Bavaria, Germany
28. Lumbering and Milling. It is well to remember, when using wood for any purpose, that it was once part of a living tree which had roots, bark, leaves, and flowers, and that the tree began life as a little sapling, which grew taller and larger for years before it could be called a tree, and that it was between fifty and a hundred years old before it was large enough to cut down for timber.
Fig. 64. Felling a Tree
The lumberman selects trees which have large, straight trunks. They are usually cut with the ax, although the first cut is often made partially through the trunk with a saw. The branches are then chopped off and the body of the tree cut into lengths convenient for handling. They are rolled into a stream and floated down the river to a sawmill, or, in case there is no river near by, are carted on sleds or wagons to the railroad and thence to the mill.
The cutting of the trees is usually done in winter, the floating of the logs, or river driving as it is called, beginning with the breaking up of the ice in the spring. River driving is a very interesting and dangerous business. Logs will often get caught sidewise and the whole river from shore to shore become jammed so tightly that hundreds of thousands of logs are stopped in their course, forming an immense dam which the lumbermen call a log jam.
Fig. 65. A Skidway of Adirondack Spruce
Fig. 66. River Drivers breaking up a “Log Jam”
Fig. 67. Log Boom and Lumber Piles at Tupper Lake, N.Y.
Fig. 68. A Modern Gang Saw—Interior of Modern Sawmill
To break up this jam very often requires much labor and great daring on the part of the drivers, who wear spiked shoes and are armed with long poles having sharp steel points. When such a jam breaks up, the crashing of the logs and rush of water can be heard for miles.
Having finally reached the mill, the logs float in the river, inclosed in a log boom, until the mill men are ready to saw them into planks.
Fig. 69. A Modern Sawmill
The boom consists of logs chained together and stretched across the river just as a fence is built on land to inclose cattle.
Fig. 70. The Circular Saw—Interior of Sawmill
The sawmill of to-day is a mass of automatic machinery, and after the log enters it is not touched by human hands until it comes out as lumber of various sizes ready to be loaded on boats or cars.
Logs are sawed into timber, planks, or boards, and these forms are called lumber.
Fig. 71. A Large Band Saw
Timber refers to all of the largest sizes, such as beams and joists. Planks are wide strips over one inch thick, and boards are one inch or less in thickness, varying in width and length. Lumber may be planed at a planing mill, and is then known as dressed lumber. It may be dressed on one, two, or all sides. Dressed stock which is free from knots, shakes, and sapwood is called clear.
Fig. 72. End of Log, showing Annual Rings and Medullary Rays
By examining the end of a log we can learn a great deal of the life of the tree. It is made up of a number of irregular rings and of lines radiating from the center and running in nearly straight lines toward the bark.
The number of rings tells us the age of the tree, as a new ring is added each year.
As the tree grows, the old wood near the center becomes compressed and dry and is known as the heartwood, while that portion between the heartwood and bark is called sapwood.
In some woods the difference between the heartwood and sapwood is very marked. In ebony, for instance, the heartwood is coal black and the sapwood white.
The sketch shows half a log, the annual rings being indicated, and also the radial lines, called medullary rays.
Fig. 73. Log cut lengthwise, showing how “Grain” is formed
Looking at the length of the log we see that the lines in a board, which we call the grain, are really the edges of the annual rings.
Fig. 74. Showing Weather Checks and “Shake”
It often happens in the forest that the wind sways the trees to such an extent that the annual rings separate and slide one within the other; this produces a defect in the wood called a shake (see s, Fig. 74).
There are other characteristics of wood known as warping and shrinkage.
Fig. 75.
After a tree has been cut down the cut end at first looks like Fig. 72. If it is allowed to lie for some time exposed to the weather, its appearance changes to Fig. 74. This is due to the evaporation of the sap, and as there is more sap toward the outside, the shrinkage is greatest there and becomes less toward the center where the heartwood is comparatively dry. This is an important fact to know, because if we had cut the log, while it was still green, into planks, as shown in Fig. 75, the boards would have curled up or warped, as shown in Fig. 76.
Fig. 76. Showing Effect of Warping
Besides warping, the evaporation of the sap causes the whole tree to shrink in diameter, and consequently our planks will tend to become narrower. This is called shrinkage, and in some woods amounts to a quarter of an inch to the foot, which means that a plank sawed twelve inches wide will, after a few months, measure only eleven and three quarter inches.
When we construct anything in wood we must always consider how the object will be affected by warping and shrinkage, remembering that the shrinkage is only across the grain.
Let us consider the problem of constructing a drawing board to see how warping and shrinkage may be overcome.
If we make it of one piece, like A (Fig. 77), the board will soon change its shape to that shown in B, which would make it useless for mechanical drawing, as a perfectly flat surface is necessary. We can overcome the warping by screwing heavy cleats on one side across the grain, as shown at C. The cleats would need to be heavy or the warping force would bend them.
A better way would be to build the board up of several narrow strips glued together, as the warping of one would be counteracted by the warping of its neighbors in opposite directions; but to make doubly sure, cleats fastened with tongue and groove joint should be added at the ends, as shown at D. This has an advantage over the first method, as the cleats in C are often in the way and make the board clumsy to handle.
Fig. 77. A Study in Construction. Methods of overcoming Warping and Shrinkage
The student will find many evidences about the house of how the woodworker has tried to prevent warping and shrinkage, as, for instance, in the paneled doors, tables, etc.
The wood of the various trees differs greatly in hardness, evenness of grain, durability, etc., and every boy should know not only what our woods are used for, but he should also know the trees when he sees them.
We are indebted to the trees for many things besides wood. They give us delightful shade and coolness in summer; many of them produce delicious fruit and nuts; from them we obtain such valuable products as maple sirup and sugar; while tar, pitch, turpentine, rubber, and tannin are only a few of the many tree products. The houses we live in, the chairs we sit on,—in fact, most of our furniture, even to the frames of our pictures, the cars we ride in, and the very pencils we write with, are of wood which was once part of the living forest.
Fig. 78. A Large Tree being moved by a Modern Tree Mover, showing Root Formation