Defining Dimension Styles

Dimension styles are your primary methods for controlling how a dimension appears. By creating a dimension style, you define exactly how that dimension is going to appear in the drawing. This includes the dimension scale, the types of arrowheads, whether or not the dimension lines appear and, if so, what color the dimension lines are.

AutoCAD allows you to control dimension styles through the use of Dimension Variables (DIMVARS). You can control these variables in two different ways. You can use the DDIM Dimension Style dialog box to access many of the variables using a graphical interface, or you can type the variable at the Command: prompt or DIM: prompt and assign it a new value. There are 68 dimension variables in AutoCAD 2002. Most of the time, adjusting the dimension variables through the Dimension Styles dialog box is the best method to use (see Figure 18.1). You can access this dialog box by choosing Dimension Styles from the Dimension toolbar or by choosing Dimension Style Manager from the Dimension menu.

The Dimension Style Manager allows you to set the current dimension style, create a new style, modify an existing style, override part of the current style, or even compare two existing styles in the same drawing. To make it even easier for you to make changes, the Style Manager gives you a graphical preview of what the currently selected dimension style will look like when used in the drawing.

Dimension Style Options

Dimension styles provide you with a method for saving different sets of dimension variables for the various types of drawings you might create. You have many options for defining how a dimension looks. To help you understand some of these options, Figure 18.2 shows you a standard linear dimension with all the parts of the dimension labeled.

To edit a dimension style, you simply open the Dimension Style Manager, select the style you want to edit, and click the Modify button. To create a new style, you can choose New in the Style Manager. In the dialog box that appears (see Figure 18.3), you can name the style and base it on an existing style.

Regardless of whether you choose to modify an existing dimension style or create a new one, the New Dimension Style dialog box shown in Figure 18.4 appears, in which you can edit the individual parts of the style.

The following exercise shows you how to create and/or edit dimension styles.

Exercise 18.1 Creating a New Dimension Style

1.	Start a new drawing in AutoCAD from scratch.
2.	From the Dimension pull-down menu, select Style. This launches the New Dimension Style dialog box, in which you can create, edit, and even compare dimension styles.
3.	All drawings start with the Standard dimension style, on which you can base new dimension styles. To create a new style, click on the New button. This opens the Create New Dimension Style dialog box.
4.	Under New Style Name, enter a name for the style using a name that you will recognize easily. This can be any name you like.
5.	Under Start With, select the dimension style you want to base the new style on. The Standard style already exists in this drawing, so you can create another style based on it.
6.	In the Use For drop-down list, select the types of dimensions you want to use the style for. If you select an option other than All, the new dimension style can be used with only the type of dimension you choose.
7.	Click Continue, and the New Dimension Style dialog box appears. You can make any changes you need to the style.
8.	In the Arrowheads area, click in the drop-down list for 1st Arrowhead and choose Closed Blank. Then click OK to return to the Dimension Style dialog box.
9.	In the list on the left, you will now see the name of the new style you just created. To edit the dimension style, make sure it is still highlighted and click on the Modify button. This returns you to the Modify Dimension Style dialog box, where you can make further changes. If you picked Modify, pick OK to return to the Dimension Style Manager.
10.	To compare two dimension styles, click the Compare button. This launches the Compare Dimension Style dialog box.
11.	At the top of this dialog box, you will see two drop-down lists. In the Compare drop-down list, select the first dimension style.
12.	In the With drop-down list, select the second style. You will immediately see a list of variables that differ between the styles (if there are any).
13.	Click Close in each dialog box to return to the drawing.

The New Dimension Style dialog box contains a tabbed interface for each set of controls for the style. A preview window accompanies each tabbed page to show you exactly what the dimension style looks like based on the current settings. This preview window enables you to make a change to the style so you can immediately see the effect of that change. The tabs in this dialog box are listed here and explained in the following sections:

• Lines and Arrows

• Text

• Fit

• Primary Units

• Alternate Units

• Tolerances

Lines and Arrows Tab

The selections found on the Lines and Arrows tab (refer to Figure 18.4) enable you to control all the dimension system variables related to the geometry of the dimension, except for the text. This tab is broken down into four distinct areas: Dimension Lines, Arrowheads, Extension Lines, and Center Marks for Circles.

The Dimension Lines section controls the appearance of the dimension line. In a linear dimension, this is the line beside or below the dimension text. In certain circumstances, you may want to create a dimension without the dimension line. For example, you may have a short dimension with large text centered inside of the dimension line. In this situation, you can suppress the first or second dimension line or both. When the dimension text is above the dimension line, the suppression options have no effect. The location of the dimension text is controlled by the Format options, which are covered in the next section.

The Extend Beyond Ticks option, which is grayed out by default, is used in conjunction with certain arrowhead types. In particular, the oblique and architectural tick arrowheads make use of this option. When one of these two arrowheads is active, you can adjust the extension of the dimension line beyond the extension lines.

A commonly used dimension line option is that of color. The default color of the dimension line is BYBLOCK, which means the line will take on the color of the dimension as a whole. The only reason to change this color is if you want a different line width for the dimension line. For example, you could have a thinner line for the dimension line versus the extension lines.

Another way to control the thickness of the plotted lines is to use lineweights. You can control extension or dimension lineweights via the Dimension Style Manager to apply to all same name dimension styles. Additionally, it should be noted that lineweights set at the dimension level override any settings to the layers or object directly. Refer to Chapter 5, “Using Linetypes and Lineweights Effectively,” for more information about using lineweights.

The options in the Extension Lines area of the dialog box perform the same functions as those under Dimension Lines. The notable exception is the Offset from Origin option. When you create a dimension, such as a linear dimension, you select two points for the dimension. These points are considered the extension line origin points. The origin offset defines the distance from these points that the extension line is started.

The Arrowheads section of the Lines and Arrows tab provides you with complete control over the arrows. AutoCAD provides you with standard arrowheads, including closed filled, open 30, dot blanked, box filled, and many others. Even with all these arrowheads, you may want to create your own. To create your own arrowheads, in the 1st and 2nd drop-down lists, select the User Arrow option. This option enables you to select any block for use as an arrow, as long as that block is already defined in the current AutoCAD drawing. The arrowhead block should be created with an overall size of one unit so it will be correctly scaled when used in the dimension. It also should be created for use at the right-hand end of the dimension. The block will be rotated for the opposite end.

Figure 18.5 shows you the dialog box in which you can enter the block name for the arrowhead.

The following exercise shows you how to create your own arrowheads.

Exercise 18.2 Creating Your Own Arrowheads

1.	Start a new drawing from scratch.
2.	Create an octagon using the POLYGON command. Make the radius of the polygon one unit.
3.	Make a block of the polygon with an insertion point at the center of the polygon. Name the block P1.
4.	From the Dimension pull-down menu, choose Style.
5.	In the Dimension Style dialog box, select the Standard style and click on the Modify button.
6.	In the Lines and Arrows tab, select User Arrow from the 1st drop-down list.
7.	In the User Arrow dialog box, enter P1 as the arrow name.
8.	Click on OK to close the Select Custom Arrow Block dialog box.
9.	Click on OK to close the Geometry dialog box and return to the New Dimension Styles dialog box.
10.	Click Close to save the dimension style changes to Standard and exit the dialog box.
11.	Create a linear dimension. Figure 18.6 shows a linear dimension created with a custom arrowhead. Figure 18.6. A linear dimension with a custom arrowhead.
12.	You can now close the drawing without saving it.

The last section of the Lines and Arrows tab controls center marks and scaling. The Center options define how center marks appear when used with radius and diameter dimensions.

Text Tab

The Text tab, shown in Figure 18.7, enables you to control how the text is displayed in your dimensions. In the Text Style drop-down list, you can select any previously defined text style. (See Chapter 15, “Text Annotation,” for more on how to define a text style.) You could also create a new text style by clicking on the button to the right of the Text Style drop-down list. This launches the Text Style dialog box, where you can create the new style.

After you select a text style, you can apply other properties, such as height and color. The Height option, in particular, depends on how the text style is defined. If the text style is defined with a fixed height, that height will be used. If the originating text style’s height is set to 0, the height specified in the Text tab will be used instead.

In addition to selecting the text style, you can control the placement of the text around the dimension line, as well as the alignment of the text in the drawing.

Fit Tab

The Fit tab of the Modify Dimension Style dialog box (see Figure 18.8) enables you to control how the text is placed when the dimension is too small for the text to fit between the extension lines.

The Fit Options section contains the following six options:

• Either the Text or the Arrows, Whichever Fits Best. When this option is selected, AutoCAD will try to determine the best method to use to create the most readable dimension. This is the default option.

• Arrows. When this option is selected, only the arrows will be forced inside of the extension lines. Text may appear outside the extension lines when the distance between the lines is too small for the text to fit otherwise.

• Text. When this option is selected, only text will be forced inside the extension lines. Arrows can be pushed outside the extension lines when the distance between the lines is small enough.

• Both Text and Arrows. When this option is selected, both the text and arrows will be forced inside the extension lines, even when there is not enough room for them.

• Always Keep Text Between Ext Lines. When this option is selected, the text will always be placed between the extension lines of the dimension, regardless of whether or not it will fit.

• Suppress Arrows If They Don’t Fit Inside the Extension Lines. This option enables you to suppress the drawing of the arrows on a dimension when the text is forced inside of the extension lines.

The Text Placement options enable you to control where the text is placed in relation to the dimension line when the text is not in the default position. You can choose from three ways of handling this: You can place the text beside the line, over the line with a leader, or over the line without a leader.

Probably the most important options in the Fit tab of the Dimension Style dialog box are the Scale options. There are two scale options: Overall Scale and Scale to Layout. The Overall Scale controls how large all the features of the dimension (such as arrowheads) will appear in the drawing. This scale is directly related to the final plot scale for the drawing. For example, if you are plotting at an architectural scale of 1/4 inch = 1'–0", your Overall Scale factor should be 48. You obtain this value by inverting the desired plot scale. In another instance, a scale such as 1:50 equates to 1/50 = 1, so the overall scale factor is 600.

When you set the scale factor, you define a scale multiplier by which all dimension size variables are multiplied. For example, arrowheads default to 0.18 units in size. If you have a scale factor of 48, the 0.18 is multiplied by 48 to arrive at the current size, correctly scaled for plotting.

If you are going to dimension in a paper space layout, you can leave the Overall Scale factor set to 1, or you can turn on the Scale to Layout option. The Scale to Layout option sets the dimension variable DIMSCALE to 0. In layout, a default value of 1.0 will be used. In this situation, when you are working in a model space viewport in layout, you can create a dimension in either space, and it will be scaled correctly. This assumes that you have used the ZOOM command to correctly scale the geometry in the model space viewport. See Chapter 19, “Paper Space Layouts,” for more information about layouts and working with model space viewports.

Primary Units Tab

The Primary Units tab (shown in Figure 18.9) is used to define the units that dimensions will use in their text. Unfortunately, AutoCAD does not automatically set the dimension units to match your Units setting in AutoCAD. Therefore, you must correctly define the units for your dimensions separately.

In the Linear Dimensions section of the tab, you can select the type of units, precision of the display, and even prefixes and suffixes. For example, if you select architectural units, you can select the precision with which the units will be displayed, how fractions are drawn (horizontal, slanted, or not stacked), and whether you want to append FT or IN to the dimension as a suffix. One important option in this section of the dialog box is the Round Off option, which enables you to define the increment to which the dimension measurements are rounded off.

The Measurement Scale option is used to adjust how the distance between the start and end points of the dimension is measured. Most of the time, this option is used when dimensions are drawn in a layout. When you place a dimension in a layout, it measures the dimension in layout units, not model space units.

In a viewport that is scaled to 1/4" = 1'–0", for example, a 4-foot line will measure 1 inch. This is because the underlying scale factor differs 1/48 between layout and model space. Just as you have to adjust the overall scale factor of a dimension style for model space, you must adjust the linear scale to match layout. It is calculated in the same way as the overall scale factor. In the previous example, a linear scale of 48 is correct.

Zero Suppression is used to control when a 0 appears in a dimension. For example, 6' is a valid dimension in architectural units. However, 6' is easily confused with 6", especially if the blueprint of the drawing is not very good. In both cases, the leading or trailing zeros have been suppressed. These dimensions read much easier as 6'-0" and 0'-6". You can set this up by disabling zero suppression for feet and inches. You can also control zero suppression for leading and trailing zeros such as 0.6 and 6.000.

Lastly, you can set the options for angular dimensions. Here you can define what unit format angles are read back and the precision of the angle measurements. Like linear dimensions, angles also have a setting for zero suppression.

Alternate Units Tab

The Alternate Units tab enables you to display alternate units in your drawing. For example, you might have drawings with architectural units and metric units as alternate units. Figure 18.10 shows an example of alternate units used in a dimension.

When alternate units are enabled, the controls for this tab of the Modify Dimension Style dialog box are the same as those found in the Primary Units tab.

Tolerances Tab

The Tolerances tab (shown in Figure 18.11) of the Modify Dimension Style dialog box enables you to add tolerances to the end of the dimension text. These tolerances are different from those related to the Tolerance command discussed in Chapter 17, “Productive Dimensioning.”

Actually, there are five different types of tolerances, each of which is briefly described in the following list:

• None. No tolerances are used in the dimension.

• Symmetrical. The tolerance is applied with a high and low limit that are the same. For example, 1.00 +/- 0.1 is a symmetrical tolerance.

• Deviation. The tolerance is applied with a high and low limit that can differ. As long as the object is manufactured within the limit, it is acceptable.

• Limits. The tolerance completely replaces the dimension. As long as the object is manufactured within the tolerances, it is acceptable.

• Basic. No tolerance is used, but a box is drawn around the dimension to help emphasize it.

After you select the tolerance method, you can apply an upper and lower value, as well as justification of the text in the dimension line. Figure 18.12 shows a dimension with a symmetrical tolerance applied.

The following exercise ties together all the information you have learned in this chapter so far. It shows you how to quickly and easily set up a complete dimension style for use in AutoCAD.

Exercise 18.3 Creating a Dimension Style for a Mechanical Drawing

1.	Start a new drawing from scratch.
2.	From the Dimension menu, choose Style.
3.	In the Dimension Style dialog box, click on New and give the new style the name MECH1 .
4.	Click on Continue.
5.	In the Center Marks for Circles area of the Lines and Arrows tab, select Line.
6.	In the Arrowheads area, select Dot for 1st arrowhead. The 2nd arrowhead will automatically change to match the 1st.
7.	In the Extension Lines area, select red as the color.
8.	Click on the Text tab.
9.	In the Text Placement section, set the Vertical option to Above.
10.	In the Text Alignment area, turn on Aligned with Dimension Line.
11.	Click on the Primary Units tab and, in the Linear Dimension area, set the Precision to 0.00.
12.	In the Angular Dimensions area, set the Precision to 0.0.
13.	Under the Text tab panel, set the Text dimension color to green.
14.	Click on the Tolerances tab and set the Tolerance Format Method to Symmetrical.
15.	Set the Upper Value to 0.2.
16.	Click on OK to close the Dimension Style dialog box.
17.	Click on the MECH1 style, and then click the Set Current button in the upper-right portion of the dialog box.
18.	Click Close to save and exit the Dimension Style dialog box and return to AutoCAD.
19.	Create a couple of linear dimensions in this style. Figure 18.13 shows a few possibilities you could create using the MECH1 dimension types. After this you can close the drawing without saving. Figure 18.13. A few dimensions created with the MECH1 dimension style.

Now you know about the processes and steps for working with dimension styles. The following section introduces some important tips that will help you optimize your dimension styles.

Tips for Creating Effective Dimension Styles

The following list offers a few tips and techniques concerning dimension styles:

• Create all necessary styles and save them in a drawing template. That way, you never have to re-create the same styles and can easily load them into new drawings.

• Give your styles names that make sense to you and to others. For example, ARCH48 is more easily recognized as an Architectural dimension style for a 1/4" drawing than is a name such as STYLE1.

• Make use of families when you need your dimension styles to change slightly when you’re using different dimension types. This saves you from having to set dimension styles every time you change dimension types such as linear or angular.