Editing Dimensions
After you draw dimensions, you can edit the position of the various parts of each dimension and change the contents of the dimension text. AutoCAD groups all the parts of a dimension into a single object.
Figure 14-9: Examples of additional dimensioning commands.
Editing dimension geometry
The easiest way to change the location of dimension parts is to use grip editing, which I describe in Chapter 10. Just click a dimension, click one of its grips, and maneuver away. You'll discover that certain grips control certain directions of movement. In general, selecting a dimension displays grips at the text, the ends of the dimension lines, and the defpoints. Experiment for a few minutes to see how they work.
In AutoCAD 2012, dimensions join the group of objects that feature multi-function grips. Click the text grip on a linear dimension and use the grip menu to adjust the text location. Click an arrow grip and you can create a continuous or baseline dimension from that end of the dimension, or you can flip the arrow. You can do these things by selecting a dimension and changing items in the Properties palette, but the multi-function grips make it a lot more efficient.
If you want to change the look of a component of a specific, individual dimension (for example, substitute a different arrowhead or suppress an extension line), use the Properties palette. (See Chapter 11 for more on the Properties palette.) All the dimension settings in the New/Modify Dimension Style dialog boxes (see “Adjusting style settings,” earlier in this chapter) are available in the Properties palette when you select one or more dimensions.
More fine tweaking
In manual drafting, it's considered bad form to cross object lines (that is, real geometry) with dimension lines or extension lines. Dimension Break (DIMBREAK) prompts you to select a dimension and then an object to break it. In Figure 14-8, earlier in this chapter, the right extension line of the 3.50 horizontal dimension is broken by the lower extension line of the 1.50 vertical dimension.
The Dimension Space (DIMSPACE) command applies a specified separation between existing linear or angular dimensions. Spacing dimensions equally — if you don't use the DIMBASELINE command as they're created — requires tedious manipulation with Snap and MOVE.
If you select one or more dimensions and right-click, the menu displays a number of useful options for overriding dimension settings or assigning a different style.
When you change a setting in the Properties palette, you're overriding the default style setting for that dimension. If you need to make the same change to a bunch of dimensions, it's usually better to create a new dimension style and assign that style to them. You can use the Properties palette or the right-click menu to change the dimension style that's assigned to one or more dimensions.
You can use the Properties palette to turn on AutoCAD's background mask feature (described in Chapter 13) for the text of individual dimensions: Select the dimensions, display the Text area in the Properties palette, and find the Fill Color item. Click in the list box, scroll down, and select Background to use the drawing background color (which usually gives the best results). To ensure that dimension text lies on top of other objects, use the DRAWORDER or TEXTTOFRONT command — see Chapter 13 for more information.
The AutoCAD EXPLODE command on the Home tab's Modify panel will blow a dimension to smithereens — or at least into a bunch of line and multiline text objects. Don't do it! Exploding a dimension makes it much harder to edit cleanly and eliminates AutoCAD's ability to update the dimension text measurement automatically.
Editing dimension text
In most cases, you shouldn't have to edit dimension text. Assuming that you draw your geometry accurately and pick the dimension points precisely, AutoCAD displays the right measurement. If you change the size of the associated object, AutoCAD updates the dimension and its measurement. However, you may occasionally want to override the dimension text (that is, replace it with a different measurement) or add a prefix or a suffix to the true measurement.
AutoCAD creates dimension text as multiline text, so dimension text has the same editing options as ordinary text. Unfortunately, the right-click menu for dimension objects doesn't include a Text Edit option. You can use the Text Override field in the Properties palette or type ED (the keyboard shortcut for the DDEDIT command) to edit dimension text in the In-Place Text Editor.
AutoCAD displays the true dimension length as text in the actual dimension (and keeps the text up to date if you change the size or location of the object). You can override the true length by typing a specific length or other text string. You can preserve the true length but add a prefix or suffix by inserting <> (that is, the left and right angle-bracket characters) as placeholders for the dimension value. For example, if you enter <> Max., and the actual distance is 12.00, AutoCAD displays 12.00 Max. for the dimension text. If you stretch the object later on so the actual distance changes to 14.50, AutoCAD changes the dimension text automatically to read 14.50 Max. Now you can appreciate the importance of drawing and editing geometry precisely!
Avoid the temptation to override the default dimension text by replacing the angled brackets with a numeric value. Doing so eliminates AutoCAD's ability to keep dimension measurements current, but even worse, you get no visual cue that the default distance has been overridden (unless you edit the dimension text). If you're overriding dimension text a lot, it's probably a sign that the creator of the drawing didn't pay enough attention to using precision techniques when drawing and editing. I'm not going to point any fingers, but you probably know whom to talk to.
Controlling and editing dimension associativity
When you add dimensions by selecting objects or by using Object Snap modes to pick points on the objects, AutoCAD normally creates associative dimensions, which are connected to the objects and move with them. This is the case in new drawings that were originally created in any release of AutoCAD starting with 2002.
If you have to work on drawings created or last edited in versions older than AutoCAD 2002, you must set the DIMASSOC system variable to 2 before AutoCAD 2012 will create associative dimensions. An easy way to make this change for the current drawing is to open the Options dialog box (click the Application button and choose Options from the bottom of the Application Menu), click the User Preferences tab, and turn on the Make New Dimensions Associative setting. Be aware that this setting affects only new dimensions that you draw from now on — to make existing non-associative dimensions associative, use the DIMREASSOCIATE command described in the following list. Look up DIMASSOC system variable in the AutoCAD help system for more information.
You aren't likely to need any of these three commands very often, but if you do, look up the command name in the online help system:
- DIMREASSOCIATE: If you have dimensions that aren't currently associative (probably because they were created in older versions of AutoCAD) or are associated with the wrong objects, you can use the DIMREASSOCIATE command to associate them with points on the objects of your choice. DIMREASSOCIATE can be found on the Annotate tab's Dimensions panel slideout, or you can just type DRE and press Enter.
- DIMDISASSOCIATE: You can use the DIMDISASSOCIATE (DDA) command to sever the connection between a dimension and its associated object.
- DIMREGEN: In a few special circumstances, AutoCAD doesn't automatically update geometry-driven associative dimensions. (Maybe Autodesk should call them “usually-fully-awake-but-occasionally-asleep-at-the-wheel associative dimensions.”) In those cases, the DIMREGEN (no command alias) command will fix things.