Chapter 4 CAD Commands and Functions 115
Redraw/Regenerate
The
Redraw
command “cleans up” the
display by removing marker blips, etc. Some
commands automatically redraw the screen,
as when a grid is removed or visible layers are
changed. However, sometimes it is useful to
request a redraw when other operations are
being performed. The
Regenerate
command
forces the program to recalculate the objects in
the entire drawing and redraw the screen. This
operation takes longer than Redraw, especially
w
on large or complex drawings.
AutoCAD Example:
Command: regen↵
Regenerating model.
Command:
Dimensioning Commands
One of the advantages of using CAD is
automated dimensioning. In almost all drafting
applications, the drawing must be dimensioned
to show lengths, distances, and angles between
features on the objects (parts). There are five fi
basic types of dimensioning commands. These
are Linear,
r r
Angular,
r r
Diameter,
r r
Radius, and Leader,
r r
Figure 4-18.
A linear dimension measures a straight line
distance. The distance may be horizontal, verti-
cal, or at an angle. Typically, you have several
choices on how the dimension text is placed. The
text may be aligned with the dimension lines,
always horizontal on the drawing, or placed
at a specifi angle. In architectural drafting, fied
dimension text for a linear dimension is never
perpendicular to the dimension line.
An angular dimension measures the angle
between two nonparallel lines. The lines can be
actual objects or imaginary lines between an ori-
gin and two endpoints. Typically, you have the
same options for text placement as with linear
dimensions.
Diameter and radius dimensions are very
similar. A diameter dimension measures the
distance across a circle through its center. A
radius dimension measures the distance from
the center of an arc to a point on that arc. A
radius dimension can also be used for a circle,
but it is not typically used in this manner.
A leader is used to provide a specific or fi
local note. A leader consists of an arrowhead (in
some form), a leader line, and the note. Often,
an optional shoulder is placed on the end of the
leader before the note.
AutoCAD Example:
Command: dim↵
Dim: horizontal↵
Specify fi rst extension line origin or select object:
(pick the fi rst endpoint of the horizontal distance) fi
Specify second extension line origin:
(pick the second
endpoint of the horizontal distance)
Specify dimension line location or [Mtext/Text/Angle]:
(drag the dimension to the correct location)
Enter dimension text 15.500:
(enter a value for
the dimension text or press
[Enter]
to accept the
default actual distance)
Dim: vertical↵
Specify fi rst extension line origin or select object:
(pick the fi rst endpoint of the vertical distance) fi
Specify second extension line origin:
(pick the second
endpoint of the vertical distance)
Specify dimension line location or [Mtext/Text/Angle]:
(drag the dimension to the correct location)
Enter dimension text 6.000:
(enter a value for
the dimension text or press
[Enter]
to accept the
default actual distance)
Dim:
(press
[Esc]
to exit dimension mode)
Command:
Drawing Aids
Drawing aids are designed to speed up the
drawing process and, at the same time, maintain
Figure 4-18. Common types of dimensions that
appear on a CAD drawing.