Chapter 7: Dimensioning

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Chapter 7 Dimensioning
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After completing this Chapter, you will be able
to use the followingfeatures

• Dimension Terminology
• Associative/Non-Associative Dimensioning
• Linear Dimensioning
• Aligned Dimensioning
• Ordinate Dimensioning
• Radius and Diameter Dimensioning
• Arc Length Dimensioning
• Angular Dimensioning
• Baseline and Continue Dimensioning
• Dimension Break
• Quick Dimensioning
• Leaders with annotation and geometric tolerance
• Center Marks
• Oblique Dimensioning
• Editing dimension text
• Dimension styles
• Overriding the Dimension Feature
• Updating Dimensions

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Dimensioning Terminology
Parts that make up dimensions in AutoCAD.
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Associative/Non-Associative Dimensioning
Dimensions in AutoCAD can be drawn as
associative, non-associative, or exploded,
depending on the setting of the DIMASSOC
dimensioning system variable. The setting for
associative dimensions is 2, non-associative is
1, and exploded dimensions is 0. Associative
dimension becomes associated with an object by
selecting points on the object (using an Object
Snap mode) when prompted to do so during a
dimensioning command. If the object is
subsequently modified in a manner that changes
the location(s) of one or both of the selected
points, the associated dimension is automatically
updated to correctly indicate the new distance or
angle.
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Non-associative dimensions are drawn while the
DIMASSOC dimensioning system variable is set to
1. The separate parts of the non-associative
dimension are, like those of the associative
dimensions, considered members of a single object
when any of them are selected for modifying.
However, if the object that was dimensioned is
selected for modifying without selecting the
dimension, the dimension itself will remain
unchanged. Exploded dimensions are drawn while
the DIMASSOC dimensioning system variable is set
to 0, and the members are drawn as separate
objects. If one of the components of the
dimension is selected for modifying, it will be
the only one modified.
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DIMDISASSOCIATE command removes associativity
from selected associative dimensions.
DIMREASSOCIATE command associates selected
dimensions to geometric objects. When prompted,
select dimension(s) to be reassociated to
object(s) and then step through the point
selection process (using Object Snap mode) when
each extension line point is marked with an X. If
the X is in a box, then that point is already
associated with a point on an object. You may
skip this point by pressing ENTER . DIMREGEN
command updates the locations of all associative
dimensions. This is sometimes necessary after
panning or zooming, after opening a drawing that
was modified in an earlier version of AutoCAD.
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Linear Dimensioning
Creates linear dimensions.
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Linear dimensioning by selecting an Object
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Aligned Dimensioning
Creates an aligned linear dimensions.
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Ordinate Dimensioning
Ordinate dimensions measure the perpendicular
distance from an origin point called the datum to
a dimensioned feature, such as a hole in a part.
Ordinate dimensions consist of an X or Y value
with a leader line. X-datum ordinate
dimensions measure the distance of a feature from
the datum along the X axis. Y-datum ordinate
dimensions measure the distance along the Y axis.
If you specify a point, AutoCAD automatically
determines whether it is an X- or Y-datum
ordinate dimension. If the distance is greater
for the Y value, the dimension measures the X
value. Otherwise, it measures the Y value.
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Radius Dimensioning
Radius dimensions measure the radii of arcs and
circles with optional centerlines or a center
mark. If Text Placement is set to Over the
Dimension Line, with a leader, the dimension is
applied with a leader line.
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Diameter Dimensioning
Diameter dimensions measure the diameters of arcs
and circles with optional centerlines or a center
mark. If Text Placement is set to Over the
Dimension Line, with a leader, the dimension is
applied with a leader line.
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Arc Length Dimensioning
Arc Length allows you to create length dimensions
(see Figure 723) for an arc.
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Angular Dimensioning
ANGULAR DIMENSION command allows to draw angular
dimensions using three points (vertex, point,
point), between two nonparallel lines, on an arc
(between the two endpoints of the arc, with the
center as the vertex), and on a circle (between
two points on the circle, with the center as the
vertex).
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Baseline Dimensioning
Baseline dimensioning is used to draw dimensions
to multiple points from a single datum baseline.
The first extension line origin of the initial
dimension (it can be a linear, angular, or
ordinate dimension) establishes the base from
which the baseline dimensions are drawn.
AutoCAD automatically draws a dimension line/arc
beyond the initial (or previous baseline)
dimension line/arc.
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Dimension Space
The DIMSPACE command allows you to specify the
space between the dimension lines of parallel
linear or concentric arc dimensions.
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Dimension Break
The DIMBREAK command allows you to create a break
in a dimension extension line where it crosses
another line.
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Continue Dimensioning
Continue dimensioning is used for drawing a
string of dimensions, each of whose second
extension line origin coincides with the next
dimensions first extension line origin.
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Quick Dimensioning
Quick Dimensioning is used to draw a string of
dimensions between all of the end and center
points of the selected object(s).
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Multileader
MLEADER Command is used to to connect annotation
to objects or other features in the drawing.
Options include Leader Type, Leader Landing,
Content Type, Maxpoints, First Angle, and Second
Angle.
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Add Leader Command is used to add leader line and
arrow combinations to an existing multileader.
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Mutlileader Style Command is used to create or
modify multileader style. With a multileader
style, you can specify formatting for landing
lines, leader lines, arrowheads, and content.
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Tolerances
AutoCAD provides a special set of subcommands for
the two major methods of specifying tolerances
Lateral Tolerance and Geometric Tolerance.
Lateral tolerance draws the traditional symbols
and text for Limit, Plus or Minus (unilateral and
bilateral), Single Limit, and Angular tolerance
dimensioning. Lateral tolerance is the range
from the smallest to the greatest that a
dimension is allowed to deviate and still be
acceptable. Lateral tolerance and its related
settings are set in the Dimension Style Manager
dialog box (Tolerances tab).
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Dimension Style Manager dialog box (Tolerance tab
selection)
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Available tolerance methods
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Geometric tolerance draws a Feature Control Frame
for use in describing standard tolerances
according to the geometric tolerance conventions.
Geometric tolerancing is applied to forms,
profiles, orientations, locations, and runouts.
Forms include squares, polygons, planes,
cylinders, and cones.
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Geometric Tolerance dialog box
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Center Marks
DIMCENTER command creates the center mark or the
centerlines of circles and arcs.
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Oblique Dimensioning
OBLIQUE command allows to slant the extension
lines of a linear dimension to a specified angle.
The dimension line will follow the extension
lines, retaining its original direction. This is
useful for having the dimension stay clear of
other dimensions or objects in your drawing. It
is also a conventional method of dimensioning
isometric drawings.
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Editing Dimension Text
AutoCAD allows to edit dimensions with MODIFY
commands and grip editing modes. Also, AutoCAD
provides two additional MODIFY commands
specifically designed to work on dimension text
objects

• Dimedit
• Dimtedit

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Dimedit
DIMEDIT command allows to replace the dimension
text with new text, rotate the existing text,
move the text to a new location, and if
necessary, restore the text back to its home
position, which is the position defined by the
current style. In addition, you also change
the angle of the extension lines (normally
perpendicular) relative to the direction of the
dimension line.
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Available options include Home selection
returns the dimension text to its default
position. New selection change the original
dimension text to the new text. Rotate
selection change the angle of the dimension
text. Oblique selection adjusts the obliquing
angle of the extension lines for linear
dimensions.
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Dimtedit
DIMTEDIT command is used to change the location
of dimension text (with the Left/Right/Home
options) along the dimension line and its angle
(with the Rotate option).
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Available options include Left selection cause
the text to be drawn toward the left extension
line. Right selection cause the text to be
drawn toward the right extension line. Home
selection returns the dimension text to its
default position. Angle selection changes the
angle of the dimension text.
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Dimension Styles
Dimension style Manager allows to create new
styles, sets the current style, modifies styles,
sets overrides on the current style, and compares
styles. Each time a dimension is drawn it
conforms to the settings of the Dimensioning
System Variables in effect at the time. The
entire set of Dimensioning System Variable
settings can be saved in their respective states
as a Dimension Style.
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Dimension Style Manager
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Create New Dimension Style dialog box
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Modify Dimension Style dialog box Lines
selection
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Various examples with Dimension and Extension
Lines settings
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Modify Dimension Style dialog box Symbols and
Arrows selection
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Arrowhead types
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Modify Dimension Style dialog box Text selection
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Dimensioning Text with various Text appearance
selections
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Dimensioning Text with various Text placement
(horizontal) selection
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Modify Dimension Style dialog box Fit selection
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Dimensioning examples with various Fit options
Dimensioning example with various Text placement
options
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Modify Dimension Style dialog box Primary Units
selection
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Dimensioning example with various dimensioning
unit formats
Dimensioning example with prefix, suffix, and
alternate units
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Modify Dimension Style dialog box Alternate
Units selection
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Modify Dimension Style dialog box Tolerances
selection
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Overriding the Dimension Feature
DIMOVERRIDE command change one of the features in
a dimension without having to change its
dimension style or create a new dimension style.
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Updating Dimensions
DIMENSION UPDATE command permits to make selected
existing dimension(s) conform to the settings of
the current dimension style.