Figure 14-30.--Drawing the involute of a line.
An involute is the curve that might be traced by a
Figure 14-28.--Drawing an ellipse using the two-circle
point on a cord that is being unwound from a line, a
triangle, a square, or other geometric figure. Figure
14-29 shows the pin-and-string method of drawing the
is an instrument used to draw smooth irregular
involute of a pentagon.
Drawing the Involute of a Line
Look at figure 1430. To draw the involute of a line,
A spiral or involute is a constantly changing curve
extend line AB (view A). Using length AB as a radius
that winds, coils, or circles around a center point. For
and A as a center, draw a semicircle (view B). Then,
a practical example, the main spring in your watch is a
using BC as the radius and B as the center, draw a second
spiral. This section gives methods of construction for
semicircle, continuing the curve as shown in view C.
Then, with CD as the radius and C as the center, draw
the next arc as shown in view D. Proceed until the curve
is the desired size.
Drawing the Involute of a Triangle
As you draw the involute of a triangle, refer to
figure 14-3 1. Extend the sides of the triangle (view A).
Figure 14-29.--Drawing the involute of a pentagon using pin
Figure 14-31.--Drawing the involute of a triangle.