THE STEEL SQUARE The Standard Steel Square has a blade 24 inches long and 2 inches wide, and a tongue from 14 to 18 inches long and 1 inches wide. The blade is at right angles to the tongue.
The face of the square is shown in Fig. 1. It is always stamped with the manufacturer's name and number.
The reverse is the back (see Fig. 2).
The longer arm is the blade; the shorter, arm, the tongue.
In the center of the tongue, on the face side, will be found two parallel lines divided into spaces (see Fig. 1); this is the octagon scale. The spaces will be found numbered 10, 20, 30, 40, 50, 60, and 70, when the tongue is 18 inches long.
To draw an octagon of 8 inches square, draw a square 8 inches each way, and draw a perpendicular and a horizontal line through its center.
To find the length of the octagon side, place one point of a com pass on any of the main divisions of the scale, and the other point of the compass on the eighth subdivision; then step this length off on each side of the center lines on the side of the square, which will give the points from which to draw the octagon lines.
The diameter of the octagon must equal in inches the number of spaces taken from the square.
On the opposite side of the tongue, in the center, will be found the brace rule (see Fig. 3). The fractions denote the rise and run of the brace, and the decimals the length. For example, a brace of 36 inches run and 36 inches rise, will have a length of 50.91 inches; a brace of 42 inches run and 42 inches rise, will have a length of 59.40 inches; etc.
On the back of the blade (Fig. 4) will be found the board measure, where eight parallel lines running along the length of the blade are shown and divided at every inch by cross-lines. Under 12, on the outer edge of the blade, will be found the various lengths of the boards, as 8, 9, 10, 11, 12, etc. For example, take a board 14 feet long and 9 inches wide. To find the contents, look under 12, and find 14; then fol low this space along to the cross-line un der 9, the width of the board; and here is found 10 feet 6 inches, denoting the contents of a board 14 feet long and 9 inches wide.
To Find the Ali= ter and Length of Side for any Poly= gon, with the Steel Square. In Fig. 5 is shown a pentagon figure. miters of the pentagon stand at 72 degrees with each other, and are found by dividing 360 by 5, the number of sides in the pentagon. But the angle when applied to the square to obtain the miter, is only one-half of 72, or 36 degrees, and intersects the blade at 831, as shown in Fig. 5.
By squaring up from 6 on the tongue, intersecting the degree line at a, the center a is determined either for the inscribed or the circumscribed di ameter, the radii being a b and a c, respec tively.
The length of the sides will be 8R inches to the foot.
If the length of the inscribed diameter be 8 feet, then the sides would be 8 X 8f3 inches.
The figures to use for other polygons are as follows: Triangle 2038_ Square 12 Hexagon 7 Nonagon 48 Decagon In Fig. 6 the same process is used in finding the miter and side of the hexagon polygon.
To find the degree line, 360 is divided by 6, the num ber of sides, as follows: 360 - 6 = 60; and 60 - 2 = 30 degrees.
Now, from 12 on tongue, draw a line making an angle of 30 degrees with the tongue. It will cut the blade in 7 as shown; and from 7 to m, the heel of the square, will be the length of the side. From 6 on tongue, erect a line to cut the degree line in c; and with c as center, describe a circle having the radius of c 7; and around the circle, complete the hexagon by taking the length 7 m with the compass for each side, as shown.
In Fig. 7 the same process is shown applied to the octagon. The degree line in all the polygons is found by dividing 360 by the number of sides in the figure: 360 - 8 = 45; and 45 - 2 = 221 degrees.
This gives the degree line for the octagon. Complete the process as was described for the other polygons.
By using the following figures for the various polygons, the miter lines may be found; but in these figures no account is taken, of the relative size of sides to the foot as in the figures preceding: Triangle 7 in. and 4 in.