172 Section 2 Drafting Techniques and Skills
Draw a
Perpendicular
CAD
Using the 3, 4, 5 Method
(Manual Procedure)
A perpendicular is a line or plane drawn r
at a right angle (90° angle) to a given line or
plane. The following procedure uses a com-
pass and the 3, 4, 5 method to construct a line
perpendicular to an existing line.
1. Line AB is given, Figure 6-15A. Line BC
is to be drawn perpendicular to Line AB.
2. Select a unit of any convenient length and
lay off three unit segments on Line AB.
Note that these segments do not have to
cover the entire length of the line.
3. With a radius of 4 units, strike Arc C
with the center point at Point B.
4. With a radius of 5 units, strike Arc D
with the center point at Point A. The
inter section of Arc C and Arc D is Point F,
Figure 6-15B.
5. Draw Line BF. This line is perpendicular
to Line AB.
Using the Perpendicular Object
Snap (CAD Procedure)
The following procedure uses the
Perpendicular object snap to draw a line per-
pendicular to an existing line. You can also
draw lines at 90° angles using Ortho mode. It
is quicker to use Ortho mode if the existing
line is a straight horizontal or vertical line.
1. A line perpendicular to Line AB is to be
drawn. Refer to Figure 6-15A.
2. Enter the
Line
command and select the
Perpendicular object snap. Move the cursor
near the endpoint of the line. When the
Perpendicular object snap icon appears,
pick a point. You can then specify a second
point for the line. The point you pick will
be the endpoint of a line that is drawn
perpendicular to Line AB.
Figure 6-15. A line perpendicular to a given line can
be constructed using the 3, 4, 5 method.
A B
C
A
A
3 units
5 units
4
units
4
units
3 units
B
C
D
F
B
Lay Out a
Given Angle
CAD
Using a Protractor
(Manual Procedure)
1. Line AB is given, Figure 6-16. An angle
is to be drawn at 35° counterclockwise at
Point C.
2. Locate the protractor accurately along
Line AB with the vertex indicator at
Point C.
3. Place a mark at 35°. This mark is Point D.
4. Draw a line from Point C to Point D.
Angle DCB equals 35°.
Using Polar Coordinates
(CAD Procedure)
Polar coordinates are used to draw lines
at a given distance and angle from a specifiedfi
point. This is a simple way to draw inclined
lines and angles. A polar coordinate is speci-
fi ed in relation to the coordinate system origin fi
or a given point. This is very useful because it
is often necessary to locate a point relative to
an existing point on the drawing.
When entering absolute coordinates, the
format X,Y is used. When entering polar
coordinates, the format distanceangle or
@distanceangle is used. If you are locating a
point from a previous point, the format
@distanceangle is used. In most cases, angles