WOOD
[Illustration: 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.
[Illustration: 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_.
[Illustration: FIG. 65. A Skidway of Adirondack Spruce]
[Illustration: FIG. 66. River Drivers breaking up a “Log Jam”]
[Illustration: FIG. 67. Log Boom and Lumber Piles at Tupper Lake, N.Y.]
[Illustration: 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.
[Illustration: 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.
[Illustration: 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_.
[Illustration: 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_.
[Illustration: 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_.
[Illustration: 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.
[Illustration: 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_.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 78. A Large Tree being moved by a Modern Tree Mover,
showing Root Formation]