Chapter 7: Dimensioning

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 After completing this Chapter, you will be able to use the following features:

Parts that make up dimensions in AutoCAD. Dimensioning Terminology

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. Associative/Non-Associative Dimensioning

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.

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.

Creates linear dimensions. Linear Dimensioning

Linear dimensioning by selecting an Object

Creates an aligned linear dimensions. Aligned 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. Ordinate 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. Radius 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. Diameter Dimensioning

Arc Length allows you to create length dimensions (see Figure 7–23) for an arc. Arc Length 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). Angular 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. Baseline Dimensioning

The DIMSPACE command allows you to specify the space between the dimension lines of parallel linear or concentric arc dimensions. Dimension Space

The DIMBREAK command allows you to create a break in a dimension extension line where it crosses another line. Dimension Break

Continue dimensioning is used for drawing a string of dimensions, each of whose second extension line origin coincides with the next dimension’s first extension line origin. Continue Dimensioning

Quick Dimensioning is used to draw a string of dimensions between all of the end and center points of the selected object(s). Quick Dimensioning

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. Multileader

Add Leader Command is used to add leader line and arrow combinations to an existing multileader.

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.

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). Tolerances

Dimension Style Manager dialog box (Tolerance tab selection)

Available tolerance methods

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.

Geometric Tolerance dialog box

DIMCENTER command creates the center mark or the centerlines of circles and arcs. Center Marks

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. Oblique Dimensioning

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 Editing Dimension Text

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.

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.

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).

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.

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. Dimension Styles

Dimension Style Manager

Create New Dimension Style dialog box

Modify Dimension Style dialog box – Lines selection

Various examples with Dimension and Extension Lines settings

Modify Dimension Style dialog box – Symbols and Arrows selection

Arrowhead types

Modify Dimension Style dialog box – Text selection

Dimensioning Text with various Text appearance selections

Dimensioning Text with various Text placement (horizontal) selection

Modify Dimension Style dialog box – Fit selection

Dimensioning examples with various Fit options Dimensioning example with various Text placement options

Modify Dimension Style dialog box – Primary Units selection

Dimensioning example with various dimensioning unit formats Dimensioning example with prefix, suffix, and alternate units

Modify Dimension Style dialog box – Alternate Units selection

Modify Dimension Style dialog box – Tolerances selection

DIMOVERRIDE command change one of the features in a dimension without having to change its dimension style or create a new dimension style. Overriding the Dimension Feature

DIMENSION UPDATE command permits to make selected existing dimension(s) conform to the settings of the current dimension style. Updating Dimensions