Chapter 6 Basic Geometric Constructions 165
Bisect a Line
CAD
Using a Triangle and T-Square
(Manual Procedure)
The term bisect refers to dividing a line t
into two equal lengths. A line can be bisected
by using a triangle and T-square. Use the fol-
lowing procedure for this method.
1. Line AB is given, Figure 6-3A.
2. Draw 60° lines AC and BC. These lines
can also be drawn at 45°. The intersection
of these two lines is Point C.
3. Line CD, drawn perpendicular to Line
AB, bisects Line AB.
Using a Compass
(Manual Procedure)
A compass and straightedge can be used
to draw a perpendicular bisector to any given
line. This method is quick and very useful for
lines that are not vertical or horizontal. The
following procedure describes this method.
1. Line EF is given, Figure 6-3B.
2. Using E and F as centers, use a compass
to strike arcs with equal radii greater
than one-half the length of Line EF, scrib-
ing Points G and H.
3. Use a straightedge to draw Line GH.
This line is the perpendicular bisector
of Line EF.
Using the Midpoint Object Snap
or the Circle Command
(CAD Procedure)
The Midpoint object snap can be used with
the
Line
command to bisect an existing line
and locate its midpoint. After entering the
Line
command, enter the Midpoint object snap mode
before picking a starting point and pick the line
near its midpoint. The cursor will “snap” to the
midpoint and allow you to draw a line in any
direction, Figure 6-4A. To construct a perpen-
dicular bisector, use the following procedure.
1. Line EF is given, Figure 6-4B.
2. Enter the
Circle
command and draw a circle
with Point E as the center point and a radius
greater than one-half the length of Line EF.
The default option of the
Circle
command
allows you to draw a circle by specifying a
center point and a radius. Use the Endpoint
object snap to select Point E as the center
point or enter coordinates. Then, enter a
value for the radius of the circle.
3. Enter the
Copy
command and copy this
circle to the end of the line. Specify
Point E as the base point and locate the
center of the new circle at Point F.
4. Enter the
Line
command and draw a
line between the two points where the
circles intersect (Points G and H) using
the Endpoint object snap. This line is the
perpendicular bisector of Line EF.
Figure 6-3. A line can be bisected using a triangle
and T-square or a compass and straightedge.
60–
A
D
B
Bisector
C
A B
E
G
F
H
Figure 6-4. Bisecting lines using CAD. A—The Midpoint
object snap is used with the Line command to locate
the midpoint of Line AB. B—Two circles are drawn to
determine the endpoints of the perpendicular bisector.
Snap point
(Midpoint
snap)
Snap point
(Endpoint
snap)
Snap point
(Endpoint snap)
Perpendicular
bisector
New line
drawn from
midpoint
B
A