Use a divider to lay out a perpendicular FROM a

natural trigonometric functions and find the sine of

point TO a line, as shown in figure 2-26. Lightly

30°5´. Then, multiply the sine value by 10 inches

(0.50126 × 10 = 5.0126) to find the height of the

prick-punch point C, then swing any arc from C that

gauge blocks. The second method is to use a table of

will intersect line AB. Prick-punch intersections D

sine bar constants. These tables give the height

and E, as in the figure. With D and E as centers,

setting for any given angle (to the nearest minute) for

scribe two arcs that intersect at a point such as F.

a 5-inch sine bar. Tables are not normally available

Place a straightedge on points C and F. The line

for 10-inch bars because it is easy to use the sine of

drawn along this straightedge from point C to line AB

the angle and move the decimal point one place to the

will be perpendicular (90°) to line AB.

right.

Use a divider to lay out a perpendicular FROM a

Although sine bars appear to be rugged, you

point ON a line, as shown in figure 2-27. Lightly

should give them the same care as gauge blocks.

prick-punch point C on line AB. Then, set the divider

Since they are used with other tools or parts that are

to any distance to scribe arcs that intersect AB at D

heavy, they are subject to rough usage. Remove or

and E with C as the center. Punch C and E lightly.

repair scratches, nicks, and burrs. Keep them clean

With D and E as centers and with the setting of the

from abrasive dirt and sweat and other corrosive

divider increased somewhat, scribe arcs that cross at

agents. Make regular inspections to locate defects

points such as F and G. The line drawn through F and

before they affect the accuracy of the bar. When you

G will pass through point C and be perpendicular to

store sine bars for extended periods, clean all bare

line AB.

metal surfaces and then cover them with a light film

of oil. Place a cover over the sine bar to prevent

To lay out parallel lines with a divider, set the

accidental damage and to discourage corrosion.

divider to the selected dimension. Then, referring

to figure 2-28, from any points (prick-punched)

such as C and D on line AB, swing arcs EF and GH.

Then, draw line IJ tangent to these two arcs and it

will be parallel to line AB and at the selected

distance from it.

Sometimes you will need to scribe a layout that

cannot be made with conventional layout methods.

For example, you cannot readily make straight and

angular layout lines on sheet metal with irregular

edges by using a combination square set. Neither can

you mount sheet metal on angle plates in a manner

that permits scribing angular lines. Geometric

construction is the answer to this problem.

2-13

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