Look at [Fig. 111]. This has a vertical line A, and a horizontal line B. The circle is thus divided into four parts, and where these lines A, B, cross the circle are the cardinal points. Each of the four parts is called a quadrant, and each quadrant has 90 degrees.
Any line, like C, which is halfway between A and B, is 45 degrees. Halfway between A and C,[p. 103] or between B and C, like the line D, is 22 1/2 degrees.
Memorizing Angles.—It is well to try and remember these lines by fixing the angles in the memory. A good plan is to divide any of the quadrants into thirds, as shown by the points E, F, and then remember that E is 30 degrees from the horizontal line B, and that F is 60 degrees. Or, you might say that F is 30 degrees from the vertical line A, and E 60 degrees from A. Either would be correct.
Section Lining.—In representing many parts of a machine, or article, it is necessary to show the parts cut off, which must be illustrated by what is called "section lining." Adjacent parts should[p. 104] have the section lines running at right angles to each other, and always at 45 degrees.
Look at the outside and then the inside views of [Fig. 112], and you will see how the contiguous parts have the angles at right angles, and clearly illustrate how every part of the wrench is made. Skill in depicting an article, for the purpose of constructing it from the drawing, will make the actual work on the bench and lathe an easy one.
