166 Exploring Drafting
A c a d e m i c l i n k
The evolution of computer technology
and electronic communication has had a
major effect on the way drawings are made
and presented. Not long ago, manual draw-
ings were the primary means of commu-
nicating manufacturing information to trade
workers. Today, drawings are created with
computer-aided drafting programs and dis-
tributed with electronic media. They are used
by workers to program computer-controlled
machine tools. Computers then interpret the
information and manufacture parts. This is
accomplished through various phases of com-
munication—including interaction between the
drafter and the computer and the computer
and a machine.
There are literally hundreds of CAD soft-
ware programs that have been used to design
products for industrial use. Computer anima-
tion programs make it possible to communi-
cate an entire design of a product before it
is manufactured or built. Internet technology
makes it possible to send, receive, evaluate,
and modify drawings in a very short period of
time.
When compared to manual drawing tech-
niques, CAD tools have made it much simpler
to communicate information. However, it is
important to understand that as with other
communication tools, CAD is only a tool. The y
same drawing skills, visualization techniques,
and concepts practiced in manual drafting
must be understood in order to use CAD
accurately and successfully.
Minor axis
Second axis
endpoint
Center point
First axis
endpoint
Major axis
•
• •
•
•
Figure 7-15 An ellipse is drawn by defining a center
point and endpoints for the minor and major axes.
Drawing Ellipses
Ellipses are drawn with the Ellipse
command. An ellipse has a center point, a
minor axis, and a major axis. See Figure 7-15.
The axes divide the ellipse into four quad-
rants. Points for the axis endpoints and center
point can be entered at the keyboard or picked
on screen.
Elliptical arcs (portions of an ellipse) can
also be drawn by specifying start and end
angles after locating the axis endpoints. The
start and end angles represent points on the
curve relative to the angular locations of the
axis endpoints. The angles are measured
counterclockwise from the fi rst axis endpoint,
which is designated as 0°. For example, an
arc drawn with a 0° start angle and 180° end
angle represents half an ellipse.
Drawing Polygons
The Polygon command can be used to
draw regular polygons. First, the number
of sides is entered. Specifying three sides
draws an equilateral triangle. Specifying
four sides draws a square. Regular penta-
gons, hexagons, and octagons can also be
drawn.
After entering the number of sides, the cen-
ter point is specified. The command sequence fi
includes prompts for the user to inscribe or
circumscribe the polygon. As you learned
in Chapter 6, an inscribed polygon is drawn
within a circle. A circumscribed polygon is