Chapter 6 Basic Geometric Constructions 191
Constructing Circles and
Arcs
A circle is a closed plane curve, Figure 6-42.
All points of a circle are equally distant from
a point within the circle called the center. The r r
diameter is the distance across a circle passing r
through the center. The radius is one-half the
diameter.
An arc is any part of a circle or other curved
line. An irregular curve is any part of a curved
surface that is not regular. Procedures used to
construct circles and arcs are discussed in the
following sections.
Figure 6-41. Using the Scale command to reduce an
object in size. A—A corner point is selected as the base
point for the scale operation. B—A scale factor of .5 is
entered to reduce the object to half the original size.
Base
point
selected
B A
Original object Scaled object
(.5 scale factor)
Figure 6-42. A—Circles are closed plane regular
curves. B—An arc is any part of a circle. C—An
irregular curve is any part of a curved surface that is
not regular.
Circle
A
Arcs
B
Irregular curve
C
Construct a Circle
Through Three
Given Points
1. Given Points A, B, and C, draw a circle
through these points, Figure 6-43A.
2. With a straightedge, draw lines between
Points A and B, and Points B and C.
3. With a compass, construct the perpen-
dicular bisector of each line, Figure 6-43B.
4. The point of intersection of the bisectors
is the center of the circle that passes
through all three points, Figure 6-43C.
5. The radius of the circle is equal to the
distance from the center to any of the
three given points.