Tips for Editing Dimensions in AutoCAD

By Bill Fane

The easiest way to change the location of dimension parts in AutoCAD is to use grip editing. Just click a dimension, click one of its grips, and maneuver away. You’ll discover that certain grips control certain directions of movement. Selecting a dimension displays grips generally at the text, the ends of the dimension lines, and the defpoints.

In AutoCAD 2012, dimensions joined the group of objects that feature multifunction 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 multifunction grips are 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. All dimension settings in the New/Modify Dimension Style dialog boxes are available from the Properties palette when you select one or more dimensions.

Use smart breaks. In manual drafting, it’s considered bad form to cross object lines (that is, real geometry) with dimension lines or extension lines, or to have anything cross a dimension line. Dimension Break (DIMBREAK) prompts you to select a dimension and then an object to break it. The wild aspect is that it’s a smart break. If you do anything to the dimension or to the object being broken to change where they cross, the break follows accordingly — and if you change either item so that they no longer cross, the break heals itself. Better yet, if you change things again so that they cross again, the break reappears!

Use the DIMSPACE command. The Dimension Space (DIMSPACE) command applies a specified separation between existing linear or angular dimensions. If you don’t use the DimBAseline command as the dimensions are created, spacing dimensions equally afterwards will require tedious manipulation with Snap Mode and the Move command.

You don’t always have to draw everything at full size. A fundamental mantra in AutoCAD is that you should always draw everything at full size. On occasion, however, it isn’t always practical. For example, you may design a power-transmission shaft for a large machine. The shaft is 4 inches in diameter and 12 feet long. It has a variety of splines, keyways, and bearing shoulders on each end, but the 11-foot section in the middle is simply a straight cylinder. If you draw it at full size and scale the plot to fit a suitable paper size, you’ll never see the details at each end.

Common practice would be to draw the interesting end details, break out and remove the boring center section, and then bring the ends closer together. Now you can create a reasonable plot. The problem is that any dimension that crosses over the break, such as the overall length, doesn’t show the correct value. The solution is to override the value, and then to use the DIMJOGLINE command to insert a jog in the dimension line to indicate that the dimension line isn’t the true length.

In spite of the name similarities, don’t confuse DIMJOGLINE with the DimJOgged command. DIMJOGLINE is for linear dimensions, and DimJOgged is for radial dimensions.

Right-click for useful options. 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.

Sometimes, it’s better to create a new 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.

If you manually change a dimvar setting, the setting is applied to the current dimension style as an override, and all subsequent dimensions that are placed by using this style have the overridden appearance. This can cause much the same problem as overriding object properties instead of using different layers; if you edit a dimension style, all existing dimensions that use it update, including the ones that you hadn’t expected because they seem to be different from the ones you want.

Use a mask for the dimension text. You can use the Properties palette to turn on AutoCAD’s background mask feature 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 TEXTTOFRONT or DRAWORDER commands.

Don’t explode dimensions. The AutoCAD eXplode command on the Home tab’s Modify panel blows a dimension to smithereens — or at least into a bunch of line and multiline text objects. Resist the temptation. Exploding a dimension makes it much harder to edit cleanly and eliminates AutoCAD’s ability to update the dimension text measurement automatically.