The boys now took up the systematic study of tools, as Ralph suggested
that they had spent time enough on toys and curiosities.
A cutting tool must be constructed with reference to the material it
is to cut. In the machine shop, we find the angle of the cutting edge
large--often 80 degrees--while a razor has a cutting edge of about 5
degrees. All cutting tools are wedges, whether saws, chisels, planes,
axes, or knives, and the angle depends on the hardness of the material
in which it is to work. The action of the tool may be a chisel action,
a knife action, or both. In the rip saw, the teeth are really a series
of chisel edges cut in one piece of steel, while in a cross cut saw we
have a knife action for cutting the fibres, followed by a chisel action
for removing the wood.
The side view of a rip saw is shown at _a_ (Fig. 101), the end view at
_b_.
The chisel-like edges are bent outward to right and left alternately.
This is called the "set" of the teeth and its purpose is to make
the cut wider than the body of the saw, to prevent friction. As the
saw teeth pass through the wood, the fibres spring back against the
saw blade or body, and the friction makes the work almost impossible
without "set" to the teeth. All woodworking saws must be set, and
special tools called "saw sets" are sold for the purpose of bending out
the teeth.
[Illustration: Fig. 101. Teeth of rip saw]
The rip or slitting saw should only be used for cutting with the grain.
When used across the grain, the action is exactly like that of a narrow
chisel, and it will tear the fibres instead of cutting them.
The teeth of a cross cut saw are shown in Fig. 102. At _a_ is the side
view, and at _b_ the end view. The teeth are set and filed to a knife
edge. This gives two parallel lines of knife-like teeth which cut the
fibres in two parallel lines, while the body of the tooth cuts out the
wood in the form of sawdust. All woodworking saws belong to one of
these two classes, and the cutting angles of the teeth are shown in
Fig. 103.
[Illustration: Fig. 102. Teeth of cross cut saw]
[Illustration: Photograph by Helen W. Cooke. Learning to Use the Cross
Cut Saw]
[Illustration: Fig. 103]
We are very apt to regard the saw not only as a very commonplace
article, but as a fixed quantity which has always been the same and
always will be. As a matter of fact, the saw has gone through a process
of evolution the same as the electric motor, automobile, and aeroplane.
New methods of its manufacture are constantly being invented and
improvements made in its construction. Some of the steps in the process
of making a hand saw are: rolling the steel plate of which the body is
made, hardening, tempering, hammering or smithing, grinding, polishing,
filing, setting, etching, handling, and blocking.
[Illustration: Fig. 104]
The handling refers to the placing of the wooden handle and some idea
of what it means is illustrated in Fig. 104, showing two methods of
attaching the apple wood handle.
Some idea of what the grinding means is shown by the tapers, or
difference in the thickness of the steel, as shown at Fig. 105, the
thickness in one thousandths of an inch being given at the different
points. It will be noticed that not only does the blade decrease in
width from the handle out to the end of the saw, but the thickness
decreases from the teeth to the top and also from the handle out to the
end. This represents ideal saw construction, and it is found only in
the good makes.
[Illustration: Fig. 105. Thickness of saw blade]
[Illustration: Fig. 106. The back saw]
The back saw, being strengthened by a heavy piece of steel along the
top, is made of thinner material, and the tapers are not necessary, for
the back piece gives rigidity. It removes less wood, but is limited in
its action by the back. It is used chiefly by pattern makers, and for
finer bench work, such as cabinet making, but should be part of every
boy's outfit.
The compass-saw shown at Fig. 107 is used for general purposes, but is
not so necessary as the back saw. It is useful for cutting out small
openings, though it is not as valuable for this purpose as the turning
saw.
[Illustration: Fig. 107. The compass saw]
One end of the turning saw can be released from the frame by removing a
pin, passed through a small hole. This is fastened in the frame again
and made to follow a curved line like a fret or coping saw.
[Illustration: Fig. 108. The turning saw]
The number of teeth to the inch varies, and saws are rated as
four-point, five-point, etc., according to the number of points or
spaces to the inch. For very hard woods, a saw with small teeth, _i.
e._, with more points than ordinary to the inch, should be used; but a
boy who possesses one saw of each kind--a rip, a cross cut, a back saw,
and a turning saw--has all that will be required for ordinary woodwork.
[Illustration: Fig. 109. Using the rip saw and trestles]
In working with the board on trestles, the saw should be held at an
angle of about 45 degrees to the surface. When sawing a board held in
the bench vise, this is not so easily done, but the cut should at least
be started with the tool in the correct position. (Fig. 109).
The hack saw is used for cutting metal, and while not essential for
woodwork, is often valuable for cutting pieces of pipe, rivets, bolts,
screws, and nails and should be added to the outfit when the finances
will allow. (Fig. 110).
[Illustration: Fig. 110. The hack saw for cutting metal]
In fact, there is no such thing as a set of tools. Good tools only
should be bought, and the outfit at first should be simple; new ones
can be added from time to time, as they are needed. In this way one
learns the possibilities of his kit much better than by starting with
an elaborate collection.