THE USES OF THE COMPASS AND THE SQUARE
THE SQUARE.--The square is, probably, the oldest of all tools, and that,
together with the compass, or dividers, with which the square is always
associated, has constituted the craftsman's emblem from the earliest
historical times. So far as we now know, the plain flat form, which has
at least one right angle and two or more straight edges, was the only
form of square used by the workman. But modern uses, and the development
of joinery and cabinet making, as well as the more advanced forms of
machinery practice, necessitated new structural forms in the square, so
that the bevel square, in which there is an adjustable blade set in a
handle, was found necessary.
THE TRY SQUARE.--In the use of the ordinary large metal square it is
necessary to lay the short limb of the square on the face of the work,
and the long limb must, therefore, rest against the work side or edge of
the timber, so that the scribing edge of the short limb does not rest
flat against the work. As such a tool is defective in work requiring
accuracy, it brought into existence what is called the try square,
which has a rectangular handle, usually of wood, into which is fitted at
one end a metal blade, which is at right angles to the edge of the
handle. The handle, therefore, always serves as a guide for the blade in
scribing work, because it lies flat down on the work.
THE T-SQUARE is another modification of the try square, its principal
use being for draughting purposes.
THE COMPASS.--The compass is one of the original carpenter's tools. The
difference between _compass_ and _dividers_ is that compasses have
adjustable pen or pencil points, whereas dividers are without adjustable
points. Modern work has brought refinements in the character of the
compass and dividers, so that we now have the bow-compass, which is,
usually, a small tool, one leg of which carries a pen or pencil point,
the two legs being secured together, usually, by a spring bow, or by a
hinged joint with a spring attachment.
PROPORTIONAL DIVIDERS.--A useful tool is called the proportional
dividers, the legs of which are hinged together intermediate the ends,
so that the pivotal joint is adjustable. By means of this tool the scale
of work may be changed, although its widest field of usefulness is work
laid off on a scale which you intend to reduce or enlarge
proportionally.
DETERMINING ANGLES.--Now, in order to lay out work the boy should know
quickly and accurately how to determine various angles used or required
in his work. The quickest way in which to learn this is to become
familiar with the degree in its various relations.
[Illustration: _Fig. 51._]
DEFINITION OF DEGREE.--A degree is not a measure, as we would designate
a foot or a pound to determine distance or quantity. It is used to
denote a division, space, interval or position. To illustrate, look at
the circle, Fig. 51. The four cardinal points are formed by the cross
lines (A, B), and in each one of the quadrants thus formed the circle is
divided into 90 degrees. Look at the radial lines (C, D), and you will
find that the distance between these lines is different along the
curved line (E) than along the curved line (F). The degree is,
therefore, to indicate only the space, division or interval in the
circle.
THE MOST IMPORTANT ANGLE.--Most important for one to know at a glance is
that of 45 degrees, because the one can the more readily calculate the
other degrees, approximately, by having 45 degrees once fixed in the
mind, and impressed on the visual image. With a square and a compass it
is a comparatively easy matter accurately to step off 45 degrees, as it
is the line C, midway between A and B, and the other degrees may be
calculated from the line C and the cardinal lines A or B.
DEGREES WITHOUT A COMPASS.--But in the absence of a compass and when you
do not wish to step off a circle, you will in such case lay down the
square, and mark off at the outer margin of the limbs two equal
dimensions. Suppose we take 2 inches on each limb of the square. The
angle thus formed by the angle square blade is 45 degrees. To find 30
degrees allow the blade of the angle square to run from 2 inches on one
limb to 3-1/2 inches on the other limb, and it will be found that for 15
degrees the blade runs from 2 inches on one limb to 7-1/2 inches on the
other limb. It would be well to fix firmly these three points, at least,
in your mind, as they will be of the utmost value to you. It is a
comparatively easy matter now to find 10 degrees or 25 degrees, or any
intermediate line.
WHAT DEGREES ARE CALCULATED FROM.--The question that now arises is what
line one may use from which to calculate degrees, or at what point in
the circle zero is placed. Degrees may be calculated either from the
horizontal or from the vertical line. Examine Fig. 53. The working
margin indicated by the cross mark is your base line, and in specifying
an angle you calculate it from the work edge. Thus, the line A indicates
an angle of 30 degrees. The dotted line is 45 degrees.
[Illustration: _Fig. 52._]
[Illustration: _Fig. 53._]
[Illustration: _Fig. 54._]
THE DIVIDERS.--The dividers are used not only for scribing circles, but
also for stepping and dividing spaces equally. There is a knack in the
use of the dividers, where accuracy is wanted, and where the surface is
of wood. Unless the utmost care is observed, the spaces will be unequal,
for the reason that the point of the dividers will sink more deeply into
the wood at some places than at others, due to the uneven texture of the
wood grain. It will be better to make a line lengthwise, and a cross
line (A) for starting (see Fig. 54). You may then insert one point of
the dividers at the initial mark (B), and describe a small arc (C). Then
move the dividers over to the intersection of the arc (C) on the line,
and make the next mark, and so on.
Some useful hints along this same line will be found under the chapter
on Drawing, which should be carefully studied.