102 Section 1 Introduction to Drafting
application is a pull-down menu. In addition to
pull-down menus, many CAD programs have
toolbars that contain buttons. Picking a button
activates a particular command. Also, some CAD
programs have a command line. This is where
a command can be typed to activate it. Finally,
some CAD programs support the use of a tablet
to enter commands with a puck. The method in
which a command is activated does not change
the basic function of the command.
File Management
Commands
Each time you use a computer, you are
working with files. fi File management commands
allow you to begin, save, and open drawings. A
file fi is a collection of related data. When working
with a CAD program, you create, save, open, and
otherwise manipulate drawing files. Common fi
commands used to manage fi les in a CAD program fi
include the New,
w
Save, and
Open
commands.
After starting a CAD program, you typically
have a choice between beginning a new draw-
ing or opening an existing drawing. The
New
command is used to start a new drawing file. fi
This command typically gives you the option of
starting a new drawing from “scratch” or from a
template. A template is a drawing file with pre- fi
configured user settings. A template typically fi
contains settings based on a certain sheet size,
title block format, or drafting discipline. Many of
the functions discussed in this chapter can be set
in a template fi le. The template file fi is then saved fi
for future use. Drafters normally have template
fi les for a variety of applications. fi
While working on a drawing, you will want
to save information as it is added. The
Save
command is used to save a drawing. If you are
saving a drawing file for the first fi time, you will fi
be asked to specify a file name. You must also fi
specify where to save the file. CAD files fi are typi- fi
cally saved to folders on a local or network drive,
but there may be cases when you want to save to
portable media.
It is important to save your work frequently.
Every 10 to 15 minutes is recommended. This
ensures that your drawing remains intact in the
event of a power failure or system crash.
The
Open
command is used to access a
drawing that has been previously saved. You will
frequently need to recall a drawing file for con- fi
tinued work. During a typical drawing session,
you may find it necessary to have fi several draw-
ings open at the same time. Remember to save
your drawings again after making any updates
to preserve your work.
Coordinate Systems
Each line, circle, arc, or other object you
add to a drawing is located by certain points.
A line is defined by its two endpoints. A circle fi
is defi by its center point and a point along fined
the circumference. A square is located by its
four corner points. To precisely locate points for
objects, all CAD programs use standard point
location systems called coordinate systems.
The most common type of coordinate system
in a CAD program is the Cartesian coordinate
system. Points are located in this system using
three coordinate axes—the X axis, Y axis, and Z
axis. The X and Y axes are used in two-dimen-
sional drafting, Figure 4-1A. (The Z axis is used
in three-dimensional drafting and is not shown
in this example.) In 2D drafting, the X axis
represents the horizontal axis. The Y axis repre-
sents the vertical axis. The intersection of these
axes is the origin. In 2D drafting, the location
of any point can be determined by measuring
the distance, in units of measurement, from the
origin along the X and Y axes. Point locations are
designated by X and Y coordinates and are rep-
resented as (X,Y). The units of measurement for
coordinates may refer to inches, feet, or metric
units, such as millimeters.
Coordinates specified for absolute point fi
locations can be positive or negative (depend-
ing on their location in relation to the origin)
and are known as absolute coordinates. As
shown in Figure 4-1A, when used for basic 2D
drafting applications, the Cartesian coordinate
system is divided into four quadrants and points
are measured in relation to the origin (0,0). A
point located in the upper-right quadrant has
a positive X coordinate value and a positive Y
coordinate value. A point located in the lower-
right quadrant has a positive X coordinate
value and a negative Y coordinate value. Points