192 Section 2 Drafting Techniques and Skills
Figure 6-43. A circle that passes through three given points can be constructed with a straightedge and a compass.
A
B
C
A
A
B
C
B
A
B
C
R
C
Locate the Center of
a Circle or an Arc
The following procedure is used to locate
the center point of a circle or an arc in manual
drafting. To locate the center point of a circle
or an arc when using CAD, use the Center
object snap.
1. Draw two nonparallel chords (Lines AB
and BC). These lines are similar to the
lines drawn in Figure 6-43C.
2. Construct the perpendicular bisector of
each chord.
3. The point of intersection of the bisectors
is the center of the circle or arc.
Construct a Circle
Through Three
Given Points Using the
Three Points Option
The
Circle
command is used to draw
circles. This command provides a number of
options based on different drawing methods.
As discussed previously, the default option
allows you to specify a center point and a
radius. The
Three Points
option allows you to
draw a circle by picking three points on screen
or entering three coordinates. The following
procedure is used.
1. Points A, B, and C are given. Refer to
Figure 6-43A.
2. Enter the
Circle
command. Enter the
Three Points
option.
3. Select Points A, B, and C to define the fi
circle. Use object snaps, pick points on
screen, or enter coordinates. The circle
is drawn after the third point is picked.
Refer to Figure 6-43C.
CAD