Using Dimensions

Chapter 12 Using Dimensions
Before you determine the dimensions of a project, your design is in flux, and many questions
may be unanswered. After you begin dimensioning, you’ll start to see whether things fit or work
together. Dimensioning can be crucial to how well a design works and how quickly it develops. The dimensions answer questions about code conformance if you’re an architect; they answer questions about tolerances, fit, and interference if you’re involved in mechanical applications. After you andyour design team reach a design on a schematic level, communicating even tentative dimensions to others on the team can accelerate design development. Dimensions represent a point from whichyou can further develop your ideas.
With AutoCAD, you can easily add tentative or final dimensions to any drawing. AutoCAD
gives you an accurate dimension without your having to take measurements. You pick the two
points to be dimensioned and the dimension line location, and AutoCAD does the rest. AutoCAD’s
associative dimensioning capability automatically updates dimensions whenever the size or shape ofthe dimensioned object changes. These dimensioning features can save you valuable time and
reduce the number of dimensional errors in your drawings.
Topics in this chapter include the following:
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Understanding the Components of a Dimension
◆
Creating a Dimension Style
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Drawing Linear Dimensions
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Editing Dimensions
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Dimensioning Non-orthogonal Objects
◆
Adding a Note with a Leader Arrow
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Applying Ordinate Dimensions
◆
Adding Tolerance Notation

Understanding the Components of a Dimension
Before you start the exercises in this chapter, it will help to know the names of the parts of a dimension.Figure 12.1 shows a sample of a dimension with the parts labeled. The dimension line is the linethat represents the distance being dimensioned. It’s the horizontal line with the diagonal tick markson either end. The extension lines are the lines that originate from the object being dimensioned.They show you the exact location from which the dimension is taken. The dimension textis the dimension value, usually shown inside or above the dimension line.



Another component of a dimension line is the dimension line extension.This is the part of the dimension line that extends beyond the extension line. Dimension line extensions are usually used only on architectural dimensions. The extension lines usually extend beyond the dimension linesin all types of dimensions. The extension line offset from originis the distance from the beginning ofthe extension line to the object being dimensioned. The extension beyond dimension lineis the distance the dimension line extends past the extension line and is most commonly used in architectural drawings.
You can control each of these components by creating or editing dimension styles.
Dimension stylesare the settings that determine the look of your dimensions. You can store multiple styles ina single drawing. The first exercise in this chapter will show you how to create a dimension style.
Dimensioning Standards
In addition to the components of a dimension, you should know about the standards that govern the placement and style of dimensions in a drawing. Each industry has a different set of standards for text size, text style, arrow style, dimension placement, and general dimensioning methods. These issues are beyond the scope of this book; however, I urge you to become familiar with the standards associated with your industry. Many resources are available to you if you want to find out more about dimension standards. Here are a few resources on the subject:
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For mechanical drafting in the United States, check the American Society of Mechanical Engineers(ASME) website:http://www.asme.org.
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For European standards, see the International Organization for Standardization (ISO) website:
http://www.iso.org.
◆
For architectural standards in the United States, see the American Institute of Architects (AIA) website:http://www.aia.org.

Creating a Dimension Style
Dimension styles are similar to text styles. They determine the look of your dimensions as well as the size of dimensioning features, such as the dimension text and arrows. You can set up a dimension style to have special types of arrows, for instance, or to position the dimension text above orin line with the dimension line. Dimension styles also make your work easier by enabling you tostore and duplicate your most common dimension settings.
AutoCAD gives you one of two default dimension styles,ISO-25orStandard,depending on whether you use the metric or Imperial (also called English) measurement system. You’ll probably add many other styles to suit the types of drawings you’re creating. You can also create variations ofa general style for those situations that call for only minor changes in the dimension’s appearance.In this section, you’ll learn how to set up your own dimension style based on the Standard dimension style (see Figure 12.2). For metric users, the settings are different, but the overall methods are the same.



Follow these steps to create a dimension style:
1.
Open the Unit
file you edited in the preceding chapter. If you didn’t create one, use the12aunit.dwgfile and rename it Unit.dwg. Metric users should open12a-unit-metric.dwgand rename itUnit.dwg.
2.
Issue Zoom All to display the entire floor plan.
3.
Click the Dimension Style tool in the Dimensions control panel. You can also choose Format
Dimension Style or typeD↵at the Command prompt to open the Dimension Style Manager dialog box.
4.
Select Standard from the Styles list box. Metric users should select ISO-25.


5.
Click New to open the Create New Dimension Style dialog box.


6.
With the Copy Of Standard or ISO-25 name highlighted in the New Style Name input box,enter My Architectural.
7.
Click Continue to open the detailed New Dimension Style dialog box.

You’ve just created a dimension style called My Architectural, but at this point it’s identical to
the Standard style on which it’s based. Nothing has happened to the Standard style; it’s still availableif you need to use it.
Setting Up the Primary Unit Style
Now, you need to set up your new dimension style so that it conforms to the U.S. architectural style of dimensioning. Let’s start by changing the unit style for the dimension text. Just as you changed the overall unit style of AutoCAD to a feet-and-inches style for your bath drawing in Chapter 3, you must do the same for your dimension styles. Setting the overall unit style doesn’t automatically set the dimension unit style. Follow these steps:
1.
In the New Dimension Style dialog box, click the Primary Units tab.

2.
In the Linear Dimensions group, open the Unit Format drop-down list, and choose Architectural.
Notice that this drop-down list contains the same unit styles as the main Drawing
Units dialog box (choose Format Units). Metric users can skip this option.
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The Decimal Separator option a few settings below the Unit Format option lets you choose
between a period and a comma for decimal points. Metric users often use the comma for a decimal point, and U.S. users use a period. This option doesn’t have any meaning for measurements other than decimal, so it’s dimmed when the Architectural unit format is selected.
3.
Select 0´-01⁄4˝from the Precision drop-down list, just below the Unit Format list. Metric users
should select 0.00. The Precision option enables you to set the level of precision that is displayed
in the dimension text. It doesn’t limit the precision of AutoCAD’s drawing database.
This value is used to limit only the display of dimension text values.

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Every dimension style setting has an equivalent system variable. See Appendix C for more on
system variables that are directly associated with dimensions.
4.
Just below the Precision drop-down list, open the Fraction Format drop-down list, and select
Diagonal. Notice what happens to the graphic: The fractional dimensions change to show
how your dimension text will look. Metric users can skip this step, because it isn’t available
when the Decimal unit format is selected.
5.
In the Zero Suppression group in the lower-left corner, click 0 Inches to deselect this check
box. If you leave it turned on, indications of 0 inches will be omitted from the dimension text.
(In architectural drawings, 0 inches are shown as in this dimension: 12´-0˝.) Metric users can
ignore this option.If you use the Imperial measurement system, you’ve set up My Architectural’s dimension unit style to show dimensions in feet and inches, the standard method for U.S. construction documents.Metric users have changed the Precision value and kept the Decimal unit system.

Setting the Height for Dimension Text
Along with the unit style, you should adjust the size of the dimension text. The Text tab of the New Dimension Style dialog box lets you set a variety of text options, including text location relative to the dimension line, style, and height.
Follow these steps to set the height of your dimension text:
1.
Click the Text tab to display the text options.

2.
Highlight the contents of the Text Height input box.
3.
Type1/8↵to make the text1⁄8˝ high. Metric users should enter0.3↵for the text height.
Unlike the text you created in Chapter 10, you specify the text height by its final plot size. You
then specify an overall dimension scale factor that affects the sizing of all dimensioning settings,
such as text and arrows.If you want to use a specific text style for your dimensions, select a text style in the Text Style drop-down list in the Text tab. If the style you select happens to have a height specification greater than 0, that height will override any text height settings you enter in the Text tab.
Setting the Location and Orientation of Dimension Text
AutoCAD’s default setting for the placement of dimension text puts the text in line with the
dimension line, as shown in the example at the top of Figure 12.2, earlier in this chapter. However,you want the new Architectural style to put the text above the dimension line, as is done in the center of Figure 12.2. To do that, you’ll use the Text Placement and Text Alignment options in the Text tab of the New Dimension Style dialog box:
1.
In the Text Alignment group in the lower-right corner of the dialog box, click the Aligned
With Dimension Line radio button.
2.
In the Text Placement group, open the Vertical drop-down list, and select Above. The
appearance of the sample image changes to show how your new settings will look.
3.
Again in the Text Placement group, change the Offset From Dim Line value to
1⁄16. Thissetting controls the size of the gap between the dimension line and the dimension text.


Each time you change a setting, the graphic gives you immediate feedback about how your
changes will affect your dimension style.
TIP Metric users may not need to change these settings, depending on your preference for dimension styles.

Choosing an Arrow Style and Setting the Dimension Scale
Next, you’ll specify a different type of arrow for your new dimension style. For linear dimensions
in architectural drawings, a diagonal line, ortickmark, is typically used, rather than an arrow.
In addition, you want to set the scale for the graphical components of the dimension, such as
the arrows and text. Recall from Chapter 10 that text must be scaled up in size in order to appearat the proper size in the final output of the drawing. Dimensions too must be scaled so they lookcorrect when the drawing is plotted. The arrows are controlled by settings in the Symbols AndArrows tab, and the overall scale of the dimension style is set in the Fit tab.

Here are the steps for specifying the arrow type and scale:
1.
Click the Symbols And Arrows tab to display the options for controlling the arrow style and
dimension line extensions.

2.
In the Arrowheads group, open the First drop-down list, and choose Architectural Tick.
The graphic next to the arrowhead name shows you what the arrowhead looks like.
TIPSee Appendix C for details on how you can create your own arrowheads. AutoCAD also lets
you set up a separate arrow style for leaders.
3.
In the Arrowheads group, change the Arrow Size setting to1⁄8. Metric users should enter.3.Next, you need to set the behavior of the dimension line and extension lines:
1.
Click the Lines tab to display the options for controlling the dimension and extension lines.


2.
In the Dimension Lines group, highlight the value in the Extend Beyond Ticks input box,
and enter1/16. (Metric users should enter0.15.) This causes the dimension lines to extend
past the tick arrows. This is a standard graphic practice used for dimensioning linear dimensions
in architectural plans.


3.
In the Extension Lines group, change the Extend Beyond Dim Lines setting to1⁄8. Metric
users should change this to.3. This setting determines the distance the extension line
extends past the dimension line.

4.
Again in the Extension Lines group, change the Offset From Origin setting to1⁄8. Metric users should change this to.3. This sets the distance from the point being dimensioned to the beginning of the dimension extension line.

5.
Click the Fit tab of the New Dimension Style dialog box to display the options for overall
dimension scale and miscellaneous settings.


6.
Turn on the Annotative option in the Scale For Dimension Features group. You may recall
from Chapter 10 that the Annotative option allows AutoCAD to automatically scale an
object to the drawing’s annotation scale.
7.
Click OK to close the New Dimension Style dialog box. The Dimension Style Manager dialog
box opens again.

Scale for Dimensions in Legacy Drawings
Drawings created prior to AutoCAD 2008 relied on scale factors to determine the scaling of dimensions.Because it’s likely that you’ll run into legacy drawing files, here is some information about the settingsused for those earlier dimensions.
Instead of using the Annotative option, the Use Overall Scale Of option is used in the Scale For DimensionFeatures group. You select the Use Overall Scale Of radio button and enter a drawing scale factor inthe Use Overall Scale Of input box.
All the values you enter for the options in the New Dimension Style dialog box are multiplied by this Use Over all Scale Of value to obtain the final size of the dimension components. For example, the text height you entered earlier,1⁄8˝, is multiplied by 48 for a dimension text height of 6˝. For metric users, the text height of 0.3 is multiplied by 50 for a text height of 15 cm. For more on the scaling of text and other objectin AutoCAD, see Chapter 3.

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If you use the Scale Dimensions To Layout option in the Scale For Dimension Features group
of the Fit tab, AutoCAD uses the Layout view port scale to size the dimension components. See
Chapter 8 for more information about view port scale settings. This can be useful if you have a
drawing that you want to print at multiple scales.
Setting Up Alternate Units
You can use the Alternate Units tab of the New Dimension Style dialog box to set up AutoCAD to
display a second dimension in centimeters or millimeters. Likewise, if you’re a metric user, you canset up a second dimension to display feet and inches. The following exercise shows you how to setup alternate dimensions. You don’t have to do this exercise now; it’s here for your information. Ifyou like, come back later and try it to see how it affects your dimensions. You can pick up the tutorialin the next section, “Setting the Current Dimension Style.”
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If you decide later that you don’t want the alternate units to be displayed, you can turn them
off by returning to this dialog box and removing the check mark from the Display Alternate Unitscheck box.
Here are the steps for setting up alternate dimensions:
1.
In the Dimension Style Manager, select a style, and then click Modify. Or, if you want to
create a new style, click New.
2.
In the New Dimension Style dialog box, click the Alternate Units tab.

3.
Click the Display Alternate Units check box. The options in the tab become available for
your input.
4.
Select the appropriate option from the Unit Format drop-down list. U.S. users should select
Decimal to show metric alternate units. Metric users should select Architectural.
5.
Select an appropriate precision value from the Precision drop-down list.
6.
Enter a scale factor for your alternate dimension in the Multiplier For Alt Units input box.
For U.S. users, the default value is25.4. This value converts feet-and-inch dimensions to millimeters.In our metric examples, you’ve been using centimeters, so change this setting to2.54. Metric users should enter0.3937to convert centimeters to feet and inches.
7.
In the Placement group, select where you want the alternate dimension to appear in relation
to the main dimension.
8.
Click OK to close the New Dimension Style dialog box. The Dimension Style Manager dialog
box opens again.

Setting the Current Dimension Style
Before you can begin to use your new dimension style, you must make it the current default:
1.
Click My Architectural in the Styles list box in the Dimension Style Manager dialog box.
2.
Click the Set Current button at far right in the dialog box.
3.
Click Close to exit the Dimension Style Manager dialog box.
You can also select a dimension style from the Dim Style Control drop-down list in the Dimensions control panel. You’re now ready to use your new dimension style.

Fitting Text and Arrows in Tight Places
Every now and then, you’ll need to dimension a small gap or a small width of an object that won’t
allow dimension text to fit. The Fit tab includes a few other settings that control how dimensions actwhen the extension lines are too close. The Text Placement group contains three options to place thetext in tight situations:
Beside The Dimension Line Places text next to the extension line but close to the dimension line.You’ll see how this affects your dimension later.
Over Dimension Line, With Leader Places the dimension text farther from the dimension line,and includes an arrow or a leader from the dimension line to the text.
Over Dimension Line, Without Leader Does the same as the previous setting, but doesn’t include the leader.
The options in the Fit Options group let you control how text and arrows are placed when there isn’tenough room for both between the extension lines.

In the next set of exercises, you’ll use the My Architectural style you just created. To switch to
another style, open the Dimension Style Manager dialog box again, select the style you want from the Styles list, and click Set Current, as you did in the previous exercise.

Modifying a Dimension Style
To modify an existing dimension style, open the Dimension Style Manager dialog box, highlight
the style you want to edit, and then click Modify to open the Modify Dimension Style dialog box.
This is virtually identical to the New Dimension Style dialog box you’ve been working with. You
can then make changes to the different components of the selected dimension style. When you’vefinished making changes and closed both dialog boxes, all the dimensions associated with theedited style update automatically in your drawing. For example, if you decide you need to changethe dimension scale of a style, you can open the Modify Dimension Style dialog box and change theScale value in the Fit tab.
This section introduces you to the various settings that let you determine the appearance of a
dimension style.
This section doesn’t discuss every option; to learn more about the other dimensionstyle options, consult Appendix B. There, you’ll find descriptions of all the items in the NewDimension Style and Modify Dimension Style dialog boxes, plus reference material covering thesystem variables associated with each option.

TIP If your application is strictly architectural, you may want to make these same dimension stylechanges to the Acad.dwt template file or create a set of template files specifically for architectural drawings of different scales.