Part I: CAD and AutoCAD for the Theater
Chapter Twelve: Dimensioning the Drawing
- Basic Dimensions
- from baseline
- diameter and radius
- Dimension Properties
- ticks and arrows
- leader types
- alternate units
- parent and child
- Editing Dimensions
Dimensioning in AutoCAD is a joy compared to dimensioning a hand drafted drawing. AutoCAD automatically measures the distances picked or selected. Using Associative Dimensioning, editing a dimension is as simple as Stretching the pick point to a new measurement. Limit lines, leaders, arrows, measurements, tolerances, and prefixes or suffixes can all be automatically placed in the dimension.
There is no part of AutoCAD that presents a wider selection of variables than Dimensions. This section is only an introduction to Dimensions. Each release of AutoCAD adds to or alters the various Dimensions commands. Release 2000 has added several improvements to simplify and add flexibility to the dimensioning process. The best source for all the details will be your AutoCAD manual.
The DIM or DIM1 command bring up the "Dim:" prompt. All dimensioning is done from the Dim prompt. DIM1 will execute one dimension command and return to the Command prompt. DIM will continue to execute dimension commands until you press [^C] to exit DIM. Non-transparent AutoCAD commands will not work with DIM invoked. There are a lot of dimension commands. These are the basic Dimension drawing commands:
- measures and dimensions two points horizontally (in the X direction). [HOR]. Select two points, Dimension line location, Dimension Text, and text location.
- measures and dimensions two points vertically (in the Y direction). [VER]. Select two points, Dimension line location, Dimension Text, and text location. HORIZONTAL and VERTICAL are a single command in Release 13. AutoCAD determines the orientation automatically from screen picks.
- measures and dimensions the linear distance between two points. [ALI]. Select two points, Dimension line location, Dimension Text, and text location.
- measures and dimensions two points along a given angle. [ROT]. Select an angle and two points, Dimension line location, Dimension Text, and text location.
- measures and dimensions to a new point using the first point of the preceding linear dimension, and using the previous angle. [BAS]. Select the new point and Dimension text. Several Dimensions can be stacked on the same baseline.
- measures and dimensions to a new point using the last point of the preceding linear dimension, and using the previous angle. [CON]. Select the new point and Dimension text. Several Dimensions can be continued in a series.???
- measures and dimensions the angle between two lines, three points, an arc or two points on a circle. [ANG]. Select either two lines, three points, one arc (two end points and center of radius implied) or a point on a circle and a second point (the circle center is the third implied point). Select Dimension arc line location, Dimension Text, and text location. If the Dimension arc line location is picked outside the angle wedge, Angular will measure the long way around the circle.
- measures and dimensions the diameter of an arc or circle. [DIA]. Select arc or circle, Dimension text, and Dimension leader length
- measures and dimensions the radius of an arc or circle. [RAD]. Select arc or circle, Dimension text, and Dimension leader length.
- marks the center of an arc or circle. [CEN].
- SPECIAL DIMS
- dimensions ordinate (X,Y) points. [ORD]. Select point, X or Y datum, leader endpoint, and Dimension text. Ordinate dimensions are used mostly for machining and manufacturing.
- draws a dimension leader line to a text entry. [LEA]. Leader dimensions are useful for adding notes to the drawing. Leaders are not associative and cannot be edited the same way that other Dimensions can.
The default Dimension text entry is the measured length or angle of the selection, except for Ordinate Dimensions whose default is the X coordinate. AutoCAD provides Associative Dimensions. If the Dimension is stretched along with the entity dimensioned, the default Dimension text will change to reflect the new measurements.
You can add prefixes and suffixes to the default text. Greater-than and less-than symbols together  insert the default entry. Anything typed before or after will be added to the default dimension text entry. For instance, at the linear Dimension prompt, "Dimension text <2'0">:", type [this is <> or so] and press Enter. The entry appears in the drawing as, "this is 2'0" or so." If the Associative Dimension entity is stretched 1'0" longer, the entry changes to, "this is 3'0" or so."
Dimension text takes on the current text style. A simple text style (Standard, RomanS) is best. Fancy text style become unreadable when small enough to fit inside the dimension leaders of the average drawing. If the current style is vertical, change it to horizontal.
To change a text entry for an existing Dimension, type [NEWTEXT] at the DIM prompt and press Enter. Enter the new dimension text at the "Enter new dimension text" prompt and press Enter. Select the Dimension or Dimensions to change. The new dimension text entry [<>] inserts the default measurements.
Dimensions can be edited from the Command prompt. Grips are handy for quick editing of Dimensions. Click on the dimension and Grip boxes appear at the dimension text entry, the measurement end points and at the ends of the leader lines. These points can all be manipulated with the Stretch command. The leader line can be moved further away or closer to the measurement by moving the end Grip boxes in Grip Stretch mode. The measurement can be changed by Stretching either end Grip. The dimension text can be moved by Stretching the text Grip box. The leader line closes up automatically when the dimension text is moved above or below the line. Dimensions can be Copied, Mirrored, Erased, etc.
There are several Dimension editing, style and utility commands available at the DIM prompt:
- restores dimension text to its default (home) position in the associative Dimension leaders.
- allows existing associative Dimension text to be edited (described above).
- allows leader lines of associative Dimensions to be tilted.
- edit the position and orientation of a single Dimension text entry.
- change the orientation of several Dimension text entries at once.
- regenerates existing associative Dimensions to display any changes to dimension variables and style, current text style, or current units settings.
- will selectively change variables for selected dimensions. It will then have no style. Also used to update the selected dimension's style.
- changes selected dimension's variables to match an existing style.
- will save the current dimension variable settings as a style.
- examines the differences between the current style and the named style.
- used to exit DIM and return to the Command prompt. Control-C [^C] will do the same thing.
- draws a dimension leader line to a text entry. [LEA].
- the same Redraw command also works at the DIM prompt.
- lists the dimension variables and their current settings.
- changes the dimension style. Null responce will keep the current style.
- will Undo dimension changes, stepping backwards one change at a time to the beginning of the DIM session. Undo from the next Command prompt will Undo all changes in the last DIM editing session.
- There are fourty-two dimension variables listed in the Release 12 book. They govern all aspects of the drafting and display of dimensions. For full details, consult the manual. Here are a few of the more important ones:
- toggle to enable alternate dimension units. Alternate dimensions are added to the primary dimension units.
- sets alternate dimension units decimal places.
- conversion multiplication factor for alternate dimension units. A factor of (2.54) converts inch units to centimeters.
- appends a dimension text prefix, suffix or both to alternate dimension units.
- toggles associative dimensioning on and off. With associative dimensioning off, all lines, arcs, etc. for dimensions are drawn a discreet entities.
- provides stacked upper and lower tolerance dimension text based on DIMTM and DIMTP. Automatically toggles DIMTOL off.
- appends a dimension text prefix, suffix or both.
- applies a scale factor to dimension offsets, arrows, and text.
- appends specified negative tolerance to dimension text when DIMTOL or DIMLIM are on.
- appends specified positive tolerance to dimension text when DIMTOL or DIMLIM are on.
- adds dimension tolerances to the default text. If DIMTM and DIMTP agree, a single +/- tolerance is given.
Release 12 and 13 provide the DDIM dimension dialogue box. This provides a dimension dialogue box with access to dimension variables. All of the above variables and many more are easy to change in DDIM without having to look up variable names.
Copyright © 1999 Wm W Wells. All rights reserved.