154 Exploring Drafting
drafting. The graph method, discussed in
Chapter 3, is used to enlarge or reduce draw-
ings with coordinate grids. When using a
CAD program, objects can be drawn to the
desired size by defi ning coordinates or other
parameters or by scaling an original object
to a different size. Coordinate entry, scaling,
and other types of drawing functions in CAD
programs are discussed later in this chapter.
How CAD Works
A CAD drawing project starts with
the generation of a geometric model of the
proposed design. The base outline or profile fi
of the design is created fi rst and then features
are added. CAD models are created in 2D or
3D form, depending on the type of program
being used and the purpose of the project.
Instructions are given to a CAD program
through the use of commands. Commands
can be picked from “ribbon” or “command
manager” tabs, selected from pull-down
menus, or entered at the keyboard. See
Figure 7-4. Toolbars and palettes may also be
available for selecting commands. A typical
CAD software interface normally provides
a number of ways to execute commands and
functions.
Once objects are drawn, they can be
altered as needed. For example, an object
can be moved, rotated, copied, deleted, or
mirrored. An object drawn in CAD can be
manipulated in a variety of ways, making it
unnecessary to draw the object again.
Dimensions and text can be added to a
CAD drawing by selecting the appropriate
command or function and entering the
required information. The drafter can definefi
the text size, style, and orientation as needed.
CAD functions for creating text and dimen-
sions are discussed later in this text.
After a CAD drawing is completed, it
can be output in a number of ways. CAD
drawings are typically printed on a plotter,
Figure 7-5. Inkjet plotters are most commonly
used to produce CAD drawings. CAD draw-
ings may also be output to a printer, such as a
laser printer.
CAD drawings may also be converted
to an appropriate fi le format for electronic
viewing in another program. For example, a
drawing may be posted by a fi rm on a Web
site for clients or for another engineer working
Ribbon tabs
Ribbon
Coordinate display
Command line
Coordinate axes
Toolbar
Palette
Drawing area
Figure 7-4 A typical CAD program drawing display. Commands can be accessed in a variety of ways to suit
the user’s needs. (Autodesk, Inc.)