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Inside AutoCAD 14

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Productive Dimensioning

by Michael Todd Peterson

When working in a production environment, one of the more time-consuming and critical challenges is the need to dimension a drawing quickly and accurately. Then, if necessary, you must also be able to modify and correct existing dimensions just as quickly and accurately.

This chapter and Chapter 19, "Advanced Dimensioning," introduce you to various techniques necessary to dimension a drawing quickly and easily. The techniques are the same, regardless of the type of drawing you are working on, whether it is architectural, civil, or mechanical in nature.

This chapter focuses on how to become more productive when dimensioning by using AutoCAD's basic dimensioning tools. Chapter 19 focuses on how to modify existing dimensions quickly. In particular, this chapter focuses on the following topics:

Becoming Proficient at Productive Dimensioning

To become proficient at dimensioning a drawing, you need a little practice and a little understanding about some of the various options made available to you by AutoCAD. The most commonly used dimensioning type is linear dimensioning.

Linear Dimensioning

Linear dimensions, of course, define a specific length, whether it is horizontal, vertical, or aligned to the object you are dimensioning. AutoCAD provides you with five different linear dimensioning commands including DIMLINEAR, DIMCONTINUE, DIMBASELINE, DIMALIGNED, and DIMROTATED. Each of these commands is accessed through the pull-down menu (see fig. 18.1), the Dimensioning toolbar (see fig. 18.2), or the Command: prompt. You should access this command using the method you are most comfortable with.

Figure 18.1 The AutoCAD 14 Dimension pull-down menu is where you can select the various dimensioning commands.

Figure 18.2 The AutoCAD 14 Dimension toolbar provides you with other methods of accessing the dimensioning commands.

The base linear command DIMLINEAR is fairly straightforward and easy to use. But, you may not be aware of one or two options of the command, which are covered in the next section.

Linear Options

The DIMLINEAR command is based on selecting three points to create the dimension. These points are the start and endpoints, as well as the location of the dimension line. Alternatively, you can create a linear dimension by selecting only two points on the screen under certain circumstances.

When you choose the DIMLINEAR command, you are prompted to select the first extension line. Instead of selecting the first extension line, you can hit Return to sel-ect the line you want to dimension. Then, all you have to do is select the line and place the dimension. The endpoints of the dimension are automatically determined from the endpoints of the line.

This option works well when what you are dimensioning is a single line, arc, circle, or polyline segment that is precisely the length you need it to be. This method does not work in paper space but does work on internal lines of blocks and xrefs, simplifying the dimensioning process a bit.

If you use this method with a multi-segmented polyline, the segment you click on will be the segment that is dimensioned. If you use this method with a circle, you can dimension the diameter of the circle with a linear dimension. DIMLINEAR will recognize objects that it cannot dimension and will issue the following informational message: "Object selected is not a line, arc, or circle." Figure 18.3 shows you some example dimensions created with two clicks.

The DIMLINEAR by selection option, however, does not solve every situation for linear dimensions. In instances where using DIMLINEAR with the selection option does not work, you may still need to resort to using construction lines in conjunction with object snap modes. In these cases, AutoCAD Release 14's new tracking feature is very helpful. See Chapter 6, "Creating Drawings with R14" for more information on how to use tracking.

Figure 18.3 Examples of using DIMLINEAR with select object on various types of geometry.

Ultimately, to get more productivity when creating linear dimensions, you need to explore a few more commands. In particular, two to look at are DIMBASELINE and DIMCONTINUE. Both commands are used after creating an initial linear dimension to quickly create additional dimensions. These commands are discussed in the following sections.

Baseline Dimensions

Baseline dimensions are used to quickly and easily create a series of dimensions from a single basepoint. If you want to dimension various objects along a wall, but want all the dimensions to measure from one end of the wall, for example, baseline is the method to use.

To make use of the baseline command, you must create a linear, aligned, or rotated dimension before using the baseline command. After you have the initial dimension, choose Baseline from the Dimension pull-down menu or the toolbar. When inside the command, select the endpoint of the next dimension. Each dimension is then automatically placed above the previous dimension and spaced appropriately. AutoCAD remembers the last dimension placed when using the DIMBASELINE and DIMCONTINUE (to be discussed in the next section) commands. You can perform any non-dimensioning command between the use of DIMLINEAR and DIMBASELINE.

TIP: If you want to baseline a dimension that was not the most recently based dimension, you can press the Enter key at the "Specify a second extension line origin or (<select>/Undo):" prompt. This will enable you to select the dimension you want to baseline. This will work with the continue dimension type as well.

Figure 18.4 shows you the click points necessary to create a series of dimensions using the baseline command.

Figure 18.4 A set of baseline dim-ensions and the mouse clicks that created them.

The following exercise shows you how to dimension a steel plate quickly and efficiently using baseline dimensions.

CREATING LINEAR DIMENSIONS BY USING BASELINES

1. Load the drawing 18TUT01.DWG from the accompanying CD.

2. Create a linear dimension from the left end of the block to the center point of the first circle, as shown in figure 18.5.

3. Choose Dimension, Baseline from the pull-down menu.

4. When prompted for the second extension line, select a center object snap mode and select the center of the second circle.

Figure 18.5 The block with the first linear dimension applied.

5. Continue using center snap modes and select the center of the rest of the circles, moving from left to right.

6. When you are finished with the circles, select the endpoint of the upper-right corner of the block. Figure 18.6 shows you the block with all the dimensions applied.

Figure 18.6 The block dimensioned using baseline dimensions.

As you can see from this exercise, after you have created the first linear dimension, regardless of whether the dimension was created using DIMLINEAR, DIMALIGNED, or other linear commands, the block is dimensioned quickly with a minimal amount of mouse operations.

To further test the baseline command, try rotating the plate 45° before you create the first dimension. Then, create a DIMALIGNED dimension for the first dimension. When you use the baseline command again, you will see that it works perfectly.

Continue Dimensions

Continue dimensions are very similar to baseline dimensions with one exception--instead of basing all the dimensions off a single point, they are based off the endpoint of the last dimension drawn. Continue dimensions automatically line up the dimension lines to create crisp clean dimensions. For example, a wall is generally dimensioned from centerline to centerline of the components of the wall, such as doors and windows. A continue dimension type makes this very easy, whereas the earlier example of a baseline dimension will base all dimensions off a single point in the wall.

If you have to create a series of dimensions, one after the other on a single dimension line, use the continue command, because it automates the placement of additional dimensions, much like the baseline command did. Figure 18.7 shows you an example of a continue dimension.

Figure 18.7 A set of dimensions showing the use of the continue command.

Like baseline, continue dimensions rely on having one linear dimension type already created, followed by the continue dimension command.

For an exercise on how to use this command, repeat the baseline exercise, but use the continue command instead. Both commands work the same way, but just produce different results.

Aligned and Rotated Dimensions

The last two linear dimension types are aligned and rotated. Both of these types are similar to each other in the fact that they are not horizontal or vertical dimensions. Aligned and rotated dimensions are the only linear dimensions where the dimension line is not horizontal or vertical.

Aligned dimensions arrange the dimension line to match the angle produced between the start and endpoints of the dimension. Rotated dimensions have the dimension line rotated a specific angle amount before the start and endpoints are selected. Figure 18.8 shows you examples of both types of dimensions.

Figure 18.8 Two dimensions, showing the difference between an aligned and a rotated dimension.

As you can see in figure 18.8, you can use the rotate command to create linear dimensions with any orientation. The aligned command, however, is forced to align itself along the start and endpoints of the dimension. Also note that a different dimension is measured, even though both dimensions use the same endpoints.

The aligned command may be accessed through the pull-down menu, toolbar, or at the Command: prompt. The rotated command, however, is only available at the Command: prompt when you are in the DIM subsystem. You can access the DIM subsystem by typing DIM at the Command: prompt. This is the old method for dimensioning in AutoCAD Release 11 and earlier. When in the DIM subsystem, type ROTATE to access the DIMROTATE command. When you are done, exit the DIM subsystem to return to the command prompt.

The following exercise shows you how to use the rotate command to create a few dimensions. The exercise also shows you why you need to be careful when using this dimension type, because a rotated linear dimension may end up with a different measured length than the original.

CREATING A ROTATED DIMENSION

1. Load the file 18TUT02.DWG from the accompanying CD. This drawing shows three circles that you are going to dimension from center point to center point.

2. At the Command: prompt, type in the command DIM to enter the dimension subsystem.

3. Enter ROTATE at the DIM: prompt.

4. When prompted for an angle, enter 38, which sets the angle of the dimension line.

5. Select the center of the left circle as the start point.

6. Select the center of the middle circle as the end point. The distance between the left and middle circles should measure out to 4.000.

7. Press Enter to bring up the rotate command again. This time, enter an angle of 315 (45° down and to the right).

8. Select the center point of the middle circle as the start point.

9. Select the center point of the circle on the right. Figure 18.9 shows you the three circles dimensioned.

Figure 18.9 A 38-degree and a 45-degree rotated dimension showing what happens when you use the rotate command on a linear dimension.

10. When you are finished with the rotate command, type exit to return to the standard AutoCAD command prompt.

Other Dimensions

Several other dimensioning types are worth mentioning. These dimension types are not linear and serve specific purposes. Depending on your discipline, you may have a use for some of these types. For example, a mechanical part designer will make heavy use of radius and diameter dimension types, whereas a civil engineer will make use of datum dimension types.

Radius and Diameter Dimensions

Radius and diameter dimensions are used to dimension the size of an arc or circle, regardless of the type of object. If you create a polyline with an arc in it, for example, you can use either type to dimension the arc. If you select the Center Mark check box in the Dimension Styles dialog box, the center mark will automatically be used with this type of dimension when the dimension text is placed outside the circle or arc. Other than that, radius and diameter dimension types are straightforward. With these dimension types, you simply pick the arc or circle to dimension, then the dimension line location.

Angular Dimensions

Angular dimensions are used to dimension the angle between two non-parallel lines. Of course, when you dimension angles between two lines, four angles are possible, one on each side of the intersection point of the two lines. Where you place the dimension line determines which angle is measured. Like radius and diameter dimensions, angular dimensions are straightforward as well.

Ordinate Dimensions

Ordinate dimensions are used to dimension a specific coordinate such as a point from a civil survey. For example, a civil survey relies upon a set of three-dimensional data points on which to base a topography. These coordinates are labeled using an ordinate dimension type, which labels the point's exact X and Y coordinates.

When using ordinate dimensions, you may dimension the X or Y axis points, called datums. You also have the option to create a leader-like ordinate dimension that has text before or after the coordinate. Figure 18.10 shows you an ordinate dimension.

Figure 18.10 An ordinate dimension showing both X and Y datums.

The Ordinate Dimension command is located on the pull-down menu, the toolbar, and at the Command: prompt. When you select this command, you are prompted to select the feature. AutoCAD is looking for you to tell it the coordinate to dimension. After you select the coordinate, you can select the type of ordinate dimension you want to use.

The four types of ordinate dimensions are X datum, Y datum, Mtext, and Text. X and Y datum produce the corresponding coordinate. Mtext pops up the Mtext dialog box so you can add text before and after the Datum dimension. The datum dimension appears as <> in the Multiline Text Editor dialog box. Figure 18.11 shows you the Mtext dialog box when used with the ordinate Mtext option. The Text option enables you to modify the text of the Datum dimension, without having to use the Mtext editor.

WARNING: You should not delete this <> marker or the actual coordinate will not appear in the dimension.

Figure 18.11 The Multiline Text Editor dialog box showing text before and after the ordinate dimension.

The following exercise shows you how to use ordinate dimensions to dimension several survey points. In this exercise, the PDMODE system variable has been set so that points appear as crosses.

USING ORDINATE DIMENSIONS

1. Load the file 18TUT03.DWG from the accompanying CD.

2. Turn on Ortho by double-clicking on Ortho at the bottom of the screen.

3. Choose Ordinate from the Dimension pull-down menu or toolbar if it is open.

4. Using a node object snap mode, click on one of the crosses and place the dimension to the right of the point.

5. Repeat steps 3 and 4, but place the dimension above the cross this time.

6. Repeat steps 3 through 5 for several other crosses so you get a little practice. Figure 18.12 shows you this file with a few ordinate dimensions added.

Figure 18.12 The points dimensioned with ordinate dimensions.

Tolerance Dimensions

Another dimension type is the tolerance dimension. Tolerances are used to provide constraints within which you can construct the drawn object. For example, you might construct a mechanical part and specify that its length may be 2.0 CM + or -0.001 CM.

AutoCAD provides you with methods of creating tolerance dimensions. One method is to specify the tolerances in the Dimension Styles dialog box. The tolerances are then automatically added to the dimension text as you place dimensions. The second method is to use the tolerance command and place tolerance symbols on the drawing. The second method is the method discussed in the following section. Figure 18.13 shows a standard tolerance symbol inside of AutoCAD.

Figure 18.13 The tolerance dimension and its parts.

Placing Tolerance Symbols in a Drawing

Under the Dimension menu and toolbars, you find a tolerance option. Choosing this option displays the Symbol dialog box, shown in figure 18.14. The Symbol dialog box is used to select the appropriate type of tolerance you want to use, through the use of industry standard tolerance symbols.

Figure 18.14 The Symbol dialog box enables you to choose the type of tolerance you want to use.

In this dialog box, notice the several different symbols, each representing a different geometric characteristic. When you choose one of the symbols, the selected tolerance method is then placed in the tolerance dimension itself. After you choose a geometric tolerance type and click on OK, you are transferred to the Geometric Tolerance dialog box (see fig. 18.15) where you may then enter the values for the tolerances.

Figure 18.15 The Geometric Tolerance dialog box enables you to specify exact tolerances.

In the Geometric Tolerance dialog box, you can specify values for tolerances 1 and 2, as well as round symbols. You can also specify up to three datums, such as a material condition and a value for that condition. You can also specify height, projected tolerance zones, and datum identifiers.

Leader Dimensions

Leaders are a very popular method of adding notes and pointing out specific aspects of a drawing. A leader is a line with an arrowhead pointing to a specific feature with some sort of text or graphics at the end of the line. For example, you might create a wall section of a house and use leaders to point out specific materials in the section.

A leader is easily created by selecting the Leader command from the pull-down menu. When prompted for the first point, select the point where you want the arrowhead of the leader to appear. Then, you simply draw as many straight leader segments as you like. When you are done, simply hit Return, enter your text, and hit Return twice more to exit the command. This chapter will focus on several more advanced features of leaders, such as using the Mtext dialog box to enter multiline text and using splines instead of straight line segments in your leaders.

Leader Options

When you select the Leader command, you are prompted for a point. This point is, of course, the location of the arrowhead. After you select the start point and then the second point, you are presented with the options for the Leader command. Usually, you type in a single line of text to complete the Leader command. Occasionally, however, you may want to select one of the three options available to you. These options are:

Format Options

If you select the Format option, you are presented with four types of formats. These types are as follows:

Each option is discussed in the following sections.

Splines Format

The first option is Splines. A spline is a smooth curved line, instead of straight line segments. When you select this option, your leader line is drawn using the AutoCAD Spline command. Note that this is not a smooth polyline, but a true spline.

Straight Format

The Straight option creates a series of straight line segments. You may select either straight or spline, but you cannot have both. AutoCAD does not enable you to draw a leader line with both straight and curved segments. Figure 18.16 shows you one leader with splines and another leader with straight lines.

NOTE:: When working with the format options, you can only select either splines or straight line segments. The Leader command is not capable of handling both types of lines in the same leader.

Arrow Format

The Arrow option defines whether an arrowhead is drawn. If you want to change the arrowhead to something other than a standard arrow, you must do so in the Dimension Styles dialog box, discussed in Chapter 19, "Advanced Dimensioning."

Figure 18.16 A leader with splines versus one without splines.

Removing All Formatting

The None option removes all formatting, including arrowheads, and draws straight line segments.

TIP: Each of the format options must be set each time you use the Leader command. To combat having to select the options each time you use the Leader command, you might write up a script file or simple LISP routine to create your own Leader command that uses splines if you like using them (see Chapter 22, "Customizing without Programming").

Annotation Options

The annotation options provide you with some control over what is placed at the end of the leader line. When you select the annotation option, you are presented with five options at the command line: Tolerance, Copy, Block, None, and Mtext, which is the default. All text in leaders is now placed using Mtext. If you select this option, you are presented with the Multiline Text Editor dialog box, where all the options of formatting Mtext are available to you. See Chapter 16, "Text Annotation," for more information on the Mtext command.

Three of the four other annotation options enable you to place a variety of objects rather than text at the end of the leader. You can place a tolerance dimension, copy an object from somewhere else in the drawing, or insert a block. Selecting one of these options launches that particular command. The last option is none, which removes all formatting.

The following exercise shows you how to create leaders on a simple architectural wall section.

CREATING LEADERS IN AUTOCAD RELEASE 14

1. Load the file 18TUT04.DWG from the accompanying CD. Figure 18.17 shows you how the drawing should appear at the end of this exercise. Use it as a reference for completing this exercise.

Figure 18.17 The wall section as it will appear at the end of the exercise.

2. On the left side of the wall, create straight leaders by choosing the Leader command from the Dimension pull-down menu or toolbar.

3. When asked for the first point, select a point close to the arrowhead location of the 2*4 Wood Stud leader.

4. Select the second point of the leader, as shown in figure 18.17.

5. At this point, you are presented with the leader options at the Command: prompt. Press Enter to accept the default Annotation Option, which enables you to add text to your leader.

6. Type in 2*4 Wood Stud and press Enter to complete the leader.

7. Repeat steps 3 through 5 for the rest of the straight leaders shown in figure 18.17.

8. For the spline leaders shown in figure 18.17, again enter the Leader command.

9. Select your start point and a second point so you are presented with the options for the command.

10. Type F for the format options.

11. Type S for spline. Now the line is a spline. Draw the rest of the line and enter the appropriate text.

Increasing Productivity with Third-Party Programs

At this point, you have seen most of the options available to you for creating standard AutoCAD dimensions. By practicing and using the options that are available to you, you can increase your productivity to some degree in terms of dimensioning. The standard AutoCAD dimensioning commands are by no means slow, but you can increase your speed with a little help.

Many users today make use of third-party programs to help increase productivity in their respective profession. Many of these programs provide automated methods for creating these same dimensions.

An architectural modeling program, for example, enables you to create with one click all the necessary dimensions for a wall, including intersecting wall, door, and window locations, as well as overall dimensions. Then, all you have to do is correct any errors, if they exist. Both Softdesk's Auto Architect and Ketiv's ArchT are excellent examples of programs that automate the dimensioning process.

Other disciplines, such as civil engineering, may make use of programs such as Softdesk's Civil series or Eagle Point Software's civil software. Both packages again automate dimensioning tasks.

In some programs, such as Mechanical Desktop, dimensions are a critical aspect of using the program correctly. In Mechanical Desktop, you must add enough dimensions to the object to fully constrain it (fully define it). Once the object is constrained, the dimensions are parametric, meaning if you change the value of the dimension, the geometry also changes.

This list of third-party programs goes on and on. If you are using a third-party program, explore its dimensioning commands and see how much faster or easier its commands are versus the standard AutoCAD commands.

Dimensioning in Paper Space versus Model Space

When looking at productivity in terms of dimensioning a drawing, one other factor to consider is where you are placing your dimensions. You have two choices in AutoCAD: model space and paper space. Each space has pros and cons.

Pros and Cons of Model Space

Most users today dimension their drawing in AutoCAD. This comes naturally because the drawing is actually created in model space. The advantages and disadvantages are listed and briefly described.

The following are some advantages of creating dimensions in model space instead of paper space.

The following are some disadvantages of creating dimensions in model space instead of paper space.

Overall, the biggest reason to place your dimensions in model space is if you do not understand paper space and how it works. If you are not comfortable working in paper space yet, create your dimensions in model space until you do feel you are ready to work in paper space.

TIP: If you work in an environment where you constantly create drawing sheets with varying drawing scales, you should strongly consider using paper space dimensioning methods.

Pros and Cons of Paper Space

With paper space dimensioning, you place your dimensions in paper space, thus separating them from the drawing. Like model space, paper space also has advantages and disadvantages when dimensioning.

The following are some advantages of creating dimensions in paper space instead of model space.

The following are some disadvantages of creating dimensions in paper space instead of model space.

Ultimately, the decision of whether to use paper space dimensioning depends on your comfort with and understanding of paper space itself. If you are not comfortable with it, continue to place dimensions in model space.

Improving Productivity: Tips and Techniques

The following are a few techniques to help you increase your dimensioning speed when you are creating dimensions. Editing dimensions is covered in the Chapter 19, "Advanced Dimensioning."

Summary

Overall, AutoCAD Release 14's dimension commands are fairly productive and much quicker than dimensioning by hand. The key things to remember are:

The next chapter delves further into the world of dimensions and covers topics such as dimension styles, as well as editing existing dimensions, where AutoCAD is extremely fast.

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