Carpentry for Boys / In a Simple Language, Including Chapters on Drawing, Laying Out Work, Designing and Architecture With 250 Original Illustrations

by James Slough Zerbe

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 3½ inches on the other limb, and it will be found that for 15 degrees the blade runs from 2 inches on one limb to 7½ 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.

Fig. 52.

Fig. 53.	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.