To set the color of the dimension line so that it differs from that of the rest of the dimension, click the Color drop-down list and choose a color. Choose Select Color to open the Select Color dialog box if you want to use a nonstandard color. Remember, a dimension is a block — that is, it is one object. The default color is ByBlock so that dimensions take on the color of the current layer or color setting. In general, you should have a separate layer for dimensions so that the entire dimension is the color set for that layer. Use this setting only if you want the dimension lines to be a different color from your dimension layer color. The arrowheads do not have a separate color setting and always follow the dimension-line setting.

To specify a linetype for a dimension, choose one from the Linetype drop-down list. If the linetype that you want isn't on the list, then you need to load it. To do this, choose Other to open the Select Linetype dialog box. (For more information on loading linetypes, see Chapter 11.) The default lineweight is ByBlock, which means that it takes on the lineweight of the current layer. To set a lineweight for the dimension line, click the Lineweight drop-down list and choose a lineweight. In general, you want your objects to stand out, so dimensions should have a lineweight the same as, or narrower than, the objects that you're dimensioning.

The Extend Beyond Ticks text box determines how far the dimension lines extend past the extension lines. When you have arrowheads at the ends of the dimension lines, the Extension option is unavailable. However, if you choose Architectural Tick, Oblique, Dot Small, Integral, or None in the Arrowheads section of the dialog box, the Extend Beyond Ticks option becomes available. This type of extension is typical for architectural drafting. Figure 15.4 shows a dimension with an architectural tick and a 0.1-unit extension.

Figure 15.4. A typical architectural dimension showing the text above one dimension line, an architectural tick, and the dimension line extending slightly beyond the extension lines.

The Baseline spacing text box determines the distance between successive dimension lines when you create baseline dimensions with the DIMBASELINE command. This specification creates evenly spaced dimension lines. (In Chapter 14, I discuss the DIMSPACE command, which lets you evenly space any linear or angular dimensions.)

In some dimension styles, the dimension text splits the dimension line into two parts, as shown in Figure 15.5. This creates two dimension lines. You can suppress — that is, turn off — the first or second dimension line (or both dimension lines) by checking the appropriate box (or boxes). The first line is nearest where you specified the first extension-line origin. (If you selected an object instead of specifying two extension-line origins, you may not be able to predict which dimension line is the first and which is the second. Experiment.) You would usually suppress dimension lines when they interfere with other dimensions or with objects in your drawing. (The DIMBREAK command, which I cover in Chapter 14, breaks dimensions where they cross objects. You may be able to break a dimension instead of suppressing one of the dimension lines.)

Figure 15.5. A typical mechanical dimension with text splitting two dimension lines.

As with dimension lines, you can pick a color for the extension lines that differs from that of the rest of the dimension. Click the Color drop-down list and choose a color. Choose Select Color to open the Select Color dialog box if you want a nonstandard color. The default color is ByBlock so that extensions take on the color of the current layer or color setting.

You can choose a separate linetype for each extension line. Choose the linetype that you want from the drop-down lists. If the linetype that you want isn't listed, click Other to open the Select Linetype dialog box, where you can load the linetype that you need.

Extension lines typically extend slightly past the dimension line, as you can see in some of the figures in this chapter. Use the Extend Beyond Dim Lines text box to specify this extension distance.

Extension lines don't usually touch the object that they dimension to make it easier to distinguish the dimension from the object. Use the Offset from Origin text box to define the distance from the specified points on the object to the extension lines.

Extension lines usually vary in length throughout a drawing, depending on the shape of the objects that you're dimensioning. However, sometimes you may want the extension lines to all be the same length, even if they don't reach near their objects. This method avoids dimension lines crossing each other when you're dimensioning a complex shape.

To specify fixed-length extension lines, check the Fixed Length Extension Lines check box and specify the length in the Length text box.

You can suppress the first or second extension line (or both lines) so that either or both are not visible. To do this, check the appropriate box (or boxes). Figure 15.6 shows a dimension with the first extension line suppressed.

Figure 15.6. A dimension with the first extension line suppressed.

The Arrowheads section controls the arrowheads at the ends of dimension lines. You don't actually have to use arrowheads, as you saw in Figure 15.4. You can also set the first and second arrowheads individually. However, if you change the first arrowhead, the second one follows suit, assuming that you want both ends of the dimension to look the same. To specify two different arrowheads, choose an arrowhead in the first drop-down list and then in the second drop-down list.

Figure 15.7. The Symbols and Arrows tab lets you define arrowheads and fine-tune dimension symbols.

You can create and use your own arrowhead:

Figure 15.8 shows a dimension with a user arrow.

Figure 15.8. A dimension with a user arrow.

Set the size of the arrowhead in the Arrow Size text box. As explained later in this chapter in the discussion of scale, you should use the final size that you want to see when the drawing is plotted on paper.

The Center Marks section of the Symbols and Arrows tab in the New Dimension Style dialog box specifies how you want to mark the centers of arcs and circles when you choose Annotate tab

Specify the size of the center mark or centerline in the text box to the right of the Center Marks section. For center marks, the size is the distance from the intersection of the two lines to their endpoints. If you use centerlines, the size also determines the distance from the circle quadrants to the end of the centerlines.

Figure 15.9. A circle with a centerline and an arc with a center mark.

In the Dimension Break section, specify the break size. A dimension break is a gap in the dimension where it crosses an object. I discuss dimension breaks (the DIMBREAK command) in Chapter 14.

The Arc Length Symbol section is for specifying the location of the symbol used when you dimension arc lengths. By default, the symbol goes before the dimension value, but you can choose to put it on top or omit it completely.

The Radius Jog Dimension section lets you specify the angle used when you create a jogged dimension for circles or arcs with large radii. A jogged dimension is a small dimension that doesn't reach to the center of the circle or arc. For more information on jogged dimensions, see Chapter 14.

In the Linear Jog Dimension section, specify a jog height factor for linear jogs. A jog is a zigzag symbol that indicates that the object is not drawn to scale, usually due to space limitations. For more information, see Chapter 14. You specify the size in relation to the text height for the dimension. The default is 1.5 times the text height. I discuss dimension text height in the next section.

Because the Standard dimension style is closest to mechanical drafting standards, in the following exercise you start to create an architectural dimension style, using the Standard style as a base. This requires you to make a maximum number of changes, thereby letting you become as familiar as possible with the dimension style settings. Here you practice controlling dimension lines and arrows.

STEPS: Controlling Dimension Lines and Arrows

Figure 15.10. The garage elevation.

You have full control over dimension text appearance, as you do over any other text in your drawing. To specify a text style for your dimension text, choose a text style from the Text style drop-down list. You may want to create a special text style, such as Dim Text, for dimension text, to give you the flexibility to alter dimension text without changing other text in your drawing. Create the dimension text style before creating your dimension style. If you want the dimension to be annotative, its text style should also be annotative.

Choose a color from the Text Color drop-down list. You can pick a color for the dimension text that differs from that of the rest of the dimension. The default color is ByBlock so that dimensions take on the color of the current layer or color setting. Use this setting only if you want the dimension text to be a different color from your dimension layer color. To choose a nonstandard color, choose Select Color from the drop-down list to open the Select Color dialog box.

You can create a block of color around the dimension text so that if other objects are behind the dimension, you can still read the dimension text clearly. To add a color, choose one from the Fill Color drop-down list.

Choose the height for your dimension text. When you set the text style height to zero, you can set the height in the New Dimension Style dialog box. Otherwise, the text style height takes over. It's much easier to make all your dimension style adjustments in one place than to make changes in the text style as well.

Figure 15.11. The Text tab of the New Dimension Style dialog box.

If your unit type uses fractions, use the fraction height scale to set a ratio of fraction text to whole text. This option is available only if your units specify the use of fractions. You may want the fractions to be smaller than whole numbers. A scale of 0.5 makes the fractions half the size of whole numbers; the resulting overall fraction is slightly higher than the whole numbers of the dimension text.

Some dimension styles require a border around the dimension text. If you want to include a rectangular border, check the Draw Frame Around Text check box.

The Vertical drop-down list affects how text is justified relative to the dimension line. As you make changes, be sure to look at the preview to see whether the results are what you want. You have the following options:

The Horizontal drop-down list affects the placement of dimension text between the extension lines. Here again, you have a handy visual confirmation of your choice. You have the following choices:

Use the Offset from Dim Line text box to set the gap between the dimension text and the dimension line. This sets the DIMGAP system variable. If the dimension line is broken, the gap is the space between each side of the dimension text and the two dimension lines. If the dimension line is unbroken and the text is above the line, the gap is the space between the bottom of the text and the dimension line. The gap also controls the space between the box created for Basic tolerance dimensions and the text inside them. Basic tolerances are discussed in the "Formatting tolerances" section later in this chapter.

Different disciplines have different standards for aligning dimension text. The Text Alignment section of the Text tab affects how the text is aligned relative to the dimension line, as follows:

STEPS: Defining Dimension Text

The Fit Options section determines which elements are moved outside the extension lines — text, arrows, or both — when they can't fit inside the extension lines. These are among the hardest of the dimension styles options to understand, yet they can greatly affect how your dimensions appear.

Here are your choices:

The Text Placement section determines where you want the dimension text when it isn't in its default position, due to a tight fit. Your options are:

The Scale for Dimension Features section lets you specify the scale factor. The reason you need to specify a scale factor is because you may have to scale the drawing when you plot it. The scale factor adjusts the size of dimension text (unless a nonzero text style height controls the text), arrowheads, spacing, and so on. It has no effect on the content of dimension text — that is, it does not affect actual measurements. So many size options are possible in a dimension style that you could spend all day trying to multiply each size option by the scale. Then if you have to change the scale of the drawing, you would need to recalculate all the size specifications. Setting the Overall Scale factor tells AutoCAD or AutoCAD LT to automatically multiply every size specification by the scale factor.

To scale dimensions according to the scale of the layout, check the Scale Dimensions to Layout option. You would use this feature if you plan to use more than one viewport, each with a different scale factor. If not, you can choose an overall scale, which would be the scale factor that you plan to use; check the Use Overall Scale Of option and enter a scale.

The annotative feature, which is available for text, hatches, blocks, and dimensions, replaces the previous dimension scaling. Therefore, when you check the Annotative check box, the two options become unavailable.

In the Fine Tuning section, if you check the Place Text Manually option, the horizontal text placement settings are ignored, and the point that you pick at the Specify dimension line location or [Mtext/Text/Angle/Horizontal/Vertical/ Rotated]: prompt is used. Before you click, as you move the cursor along the dimension line, you can see the text following the cursor.

Check the Draw Dim Line Between Ext Lines option to force a dimension line between the extension lines, even when there isn't room for text or arrows, as shown in Figure 15.22.

Figure 15.22. A dimension with a forced dimension line.

STEPS: Setting Dimension Fit

To get the look and accuracy that you want, you should specify the format and precision of your linear dimensions. The New Dimensions Style dialog box provides settings for linear dimensions. You have the following options:

You can use the Scale Factor text box to set a scaling factor for linear dimensions, including radial and diameter dimensions, and ordinal dimensions. This factor changes the actual measurement text. For example, if you draw a line 2.5 units long and you specify a linear scale of 0.5, the object is dimensioned as 1.25 units. You could set this scale to 25.4 to use metric measurements on a drawing that you have created with U.S. measurements. This can occur if you're sending the same drawing to certain clients in the United States and other clients elsewhere in the world. You can also use this scale in conjunction with alternate units, as explained in the next section.

Check the Apply to Layout Dimension Only option to apply the linear scaling factor only to layout (paper space) dimensions.

In the Zero Suppression section, choose whether you want to suppress leading and trailing zeros. If you suppress leading zeros, a number such as 0.375 appears as .375. If you suppress trailing zeros, a number such as 3.7500 appears as 3.75.

You can use subunits with decimal units only. For example, if your units represent feet, instead of displaying a dimension value as 0.25 feet, you may want to display the measurement as 3″.

To do so, first check the Leading check box, to suppress leading zeros. Then specify the Sub-Units Factor value to set the number of subunits per unit. In the previous example, you would set the Sub-Units Factor to 12, because there are 12 inches in a foot. (If your units represent meters, you could set the Sub-Units Factor to 100 to show units of less than one in centimeters.)

Use the Sub-Units Suffix text box to specify a suffix for the dimension text. In the example you would set this value to ″, to represent inches. AutoCAD multiples the actual value (.25) by the subunit factor (12), adds the suffix, and displays the results (3″). (If your units represent meters and you want to show centimeters for subunits, set the suffix to cm.

For architectural units, you can choose to suppress 0 feet and 0 inches. If you suppress 0 feet, a number such as 0'-8″ becomes 8″. If you suppress 0 inches, a number such as 6'-0″ becomes 6'.

To get the look and accuracy that you need for angular dimensions, you should also set their format and precision. The Angular Dimensions section of the Primary Units tab lets you format angular measurements. You have the following options:

In the Zero Suppression section, choose whether you want to suppress leading and trailing zeros for angular dimensions. For example, an angle of 37.0° would appear as 37° with the trailing zero suppressed.