Dimensions
Learning Objectives
In this chapter, we introduce the first parts of AutoCAD’s extensive dimensioning capabilities and discuss the following:
At the end of this chapter, you will be able to add dimensions to your floor plan.
Estimated time for completion of chapter: 3 hours (lesson and project).
6.1 Introduction to Dimensions
Dimensioning in AutoCAD is a major topic, one so extensive that it is split into two separate discussions. In this chapter, we address the basics of what dimensions are, which ones are available, and how to use and edit them. In Chapter 13, we look at extensive customization and additional options and explore some relatively new additions to the dimensioning family: parametric dimensioning and the concept of constraints and dimension-driven design.
So, what are dimensions? They are simply visible measurements for purposes of conveying information to the audience that will be looking at your design. It is how you describe the size of the design and where it is in relation to everything else. Dimensions can be natural, meaning they display the actual value, or forced, when they display an altered value, such as when you dimension an object with a break line.
6.2 Types of Dimensions
The first step in learning dimensions is to know what is available, so you can use the appropriate type in any situation. The primary and secondary dimensions available to you are shown next. Commit them to memory, as you may need most of them on a complex project.
Primary dimensions are the dimensions used most often by the typical architectural or engineering designer:
Secondary dimensions are used less often or are quite specialized but still need to be learned:
Let us take the primary list, and discuss the dimensions one by one to understand how each is used. In each case, you need to draw the appropriate shape to practice with, then add the new dimension(s) by following the step-by-step instructions. As before, we use typing, toolbars, cascading menus, and the Ribbon. You can of course stick to just one method if you prefer. Open a new file and, if using toolbars, bring up the Dimension toolbar (Figure 6.1), adding it to those already on your screen.
Note an important point if typing dimensions: You need to type in dim and press Enter. This gets you into the dimension submenu. The command line then says Dim: and you can type in whatever dimension you want to create, usually abbreviating by typing only the first few letters, as shown (such as hor for horizontal); then press Enter again. The command then executes normally. So there is an advantage to using other input methods here rather than typing, though the differences in effort and speed are rather small. Remember also that you need to press Esc to get out of this Dim: mode and back to the regular command line.
Linear Dimensions
These are any dimensions that are strictly horizontal or vertical (Figure 6.2). We go over only the horizontal dimension, as reflected in the matrix that follows. Of course, the same steps apply to the vertical dimension and you should practice it on your own.
Step 1. Create a small to medium-size rectangle or square, as seen in Figure 6.2, and begin the linear dimension command via any of the preceding methods.
AutoCAD says: Specify first extension line origin or<select object>:
Step 2. Turn on your OSNAPs, and using ENDpoint, select the upper left corner of the rectangle or square.
AutoCAD says: Specify second extension line origin:
Step 3. Again using ENDpoint, select the upper right corner of the rectangle or square (since we are doing the horizontal dimension first). The dimension appears, attached to the movements of your mouse.
(Keyboard) AutoCAD says: Specify dimension line location or [Mtext/Text/Angle]:
(If using other three methods) AutoCAD says: Specify dimension line location or [Mtext/Text/Angle/Horizontal/Vertical/Rotated]:
Step 4. Move the mouse up and down and click where you want the dimension to go, usually a short distance from the object. It sets and the value is shown.
(Keyboard) AutoCAD says: Enter Dimension text=4.4681
(If using the other three methods) AutoCAD says: Dimension text=4.4681
Your value likely is different, of course.
Note an important distinction with the keyboard entry method. Instead of setting the value in Step 4, AutoCAD throws in one more step, call it 4b, allowing you to alter the dimension on the spot (forcing it). You can enter a new value or press Enter to accept the natural one. With the other input methods, you get no chance to alter the value until after you have already created it, a slight disadvantage in some cases.
The previous linear dimensions are by far the most common in most drawings and are also the basis for the continuous and baseline dimensions, to be covered later on. Be sure to also run through the vertical version of the linear dimension, selecting the upper right and lower right (or upper and lower left) corners of the rectangle or square. Next is the aligned dimension, which gives the true distance of a slanted surface.
Aligned Dimension
This is a dimension that measures a slanted line or object (Figure 6.3).
Step 1. Create a small to medium-size rectangle or square and chop off any corner, or just do this to your existing shape, as seen in Figure 6.3. Then, begin the aligned dimension command via any of the preceding methods.
AutoCAD says: Specify first extension line origin or<select object>:
Step 2. Turn on your OSNAPs and, using ENDpoint, select the upper left start of the slanted line.
AutoCAD says: Specify second extension line origin:
Step 3. Again, using ENDpoint, select the lower right end of the slanted line. The dimension appears.
AutoCAD says: Specify dimension line location or [Mtext/Text/Angle]:
Step 4. Move the mouse up and down and click where you want the dimension to go, usually a short distance from the object. It sets and the value is shown.
Your value likely is different, of course.
Again, note an important distinction with keyboard entry. Instead of setting the value in Step 4, AutoCAD throws in one more step, allowing you to alter the dimension on the spot. You can enter a new value or press Enter to accept the natural one. We do not detail the AutoCAD responses with keyboard entry here; the previous linear dimensions should serve as a good example.
The next two dimensions, diameter and radius, are essentially similar, although we cover them separately for clarity. Note the primary differences: the symbol indicating diameter (Ø) and the symbol for radius (R) prior to the value. Although you can set this up, by default there is no line crossing the circle halfway for radius, or all the way across for diameter, so you have to read the values carefully and look for the appropriate symbol to know what you are looking at.
Also, note the location of the values. They are positioned at roughly 10, 2, 4, and 8 o’clock relative to the circle. Do not just put them anywhere; hand-drafting rules still apply in CAD, and designers have typically left them in these positions for clarity, consistency, and style.
Diameter Dimension
This is a dimension that measures the diameter of a circle or an arc (Figure 6.4).
Step 1. Create a small to medium-size circle, as seen in Figure 6.4. Then, begin the diameter dimension command via any of the preceding methods.
AutoCAD says: Select arc or circle:
Step 2. Pick the circle and the dimension appears attached to your mouse.
AutoCAD says: Dimension text=3.1357 Specify dimension line location or [Mtext/Text/Angle]:
Your value likely is different, of course.
Step 3. Position your mouse somewhere to the upper right of the circle (rarely inside, usually outside) at 2 o’clock or at any of the other accepted positions and click. The value and the dimension are shown.
Radius Dimension
This is a dimension that measures the radius of a circle or an arc (Figure 6.5).
Step 1. Create a small to medium-size circle, as seen in Figure 6.5. Then, begin the radius dimension command via any of the preceding methods.
AutoCAD says: Select arc or circle:
Step 2. Pick the circle and the dimension appears attached to your mouse.
AutoCAD says: Dimension text=1.5679 Specify dimension line location or [Mtext/Text/Angle]:
Your value likely is different, of course.
Step 3. Position your mouse somewhere at the upper right of the circle (rarely inside, usually outside) at 2 o’clock or at any of the other accepted positions and click. The value and the dimension are set.
Angular Dimension
This is a dimension for angles between two lines or objects (Figure 6.6).
Step 1. Create two lines spread out at a random angle, as seen in Figure 6.6. Then, begin the angular dimension command via any of the preceding methods.
AutoCAD says: Select arc, circle, line, or<specify vertex>:
Step 2. Pick both lines, one after the other.
AutoCAD says: Specify dimension arc line location or [Mtext/Text/Angle/Quadrant]:
Step 3. Drag the mouse out and move it around, selecting the best position for the new dimension, and click when you find a spot you like. Be careful, as the supplement of the degree value shows if you move behind the lines, which of course may be desirable in some cases.
Your value of course may be different.
Once again, note an important distinction with keyboard entry. Instead of setting the value in Step 3, AutoCAD throws in one more step, allowing you to alter the dimension on the spot (forcing it). You can enter a new value or press Enter to accept the natural one and position the text.
Angular completes the basic set of new fundamental dimensions. Next, we have continuous and baseline, which are not really new, as we will see, but rather an extension (or automation) of the linear dimension learned earlier. We then conclude with a leader, not so much a dimension, but a useful member of that family.
Continuous Dimensions
These are continuous strings of dimensions, as seen in Figure 6.7.
A short explanation is in order, as continuous and baseline dimensions give new students some initial problems. Continuous dimensions are nothing more than a string of familiar horizontal or vertical ones. The idea here is to create one of those two types of linear dimensions, then start up the continuous dimension where you just left off and let AutoCAD quickly fill them in as you pick contact points. It is really the same as using linear dimensions over and over again but faster and more accurate since it is partially automated.
The easiest way to practice continuous dimensions is to draw a set of squares attached to each other. These represent a simplified view of building and room walls. Draw one random-sized square and copy it, endpoint (lower left corner) to endpoint (lower right corner), until you have what is shown in Figure 6.8.
The next step is to draw one horizontal linear dimension as you already have done (it could have easily been a vertical line, too, if the rectangles were stacked vertically). Locate it about where you would like the entire string to go, as seen in Figure 6.9.
This is the essential first step in creating both continuous and baseline dimensions. Now, you can practice creating continuous dimensions as outlined next.
Step 1. Once you have the squares and one linear dimension, as seen in Figure 6.9, start up the continuous command via any of the preceding methods.
AutoCAD says: Specify a second extension line origin or [Undo/Select]<Select>:
Step 2. A new dimension appears. Pick the next point (corner) along the string of rectangles and click on it (always using OSNAP points, no eyeballing).
AutoCAD says: Dimension text=1.9709
Your value, of course, may be different.
Step 3. You can continue this until you run out of objects to dimension; at that point, just press Esc. Your result is shown in Figure 6.10. Notice how all the values are neatly spaced in a row.
As you are already aware, the difference between keyboard entry and the other methods is the opportunity to enter a value other than what is given (force the dimension) when typing. You then have to repeat the continuous dimension (in other words, retype cont) to carry on.
An interesting side note concerns what happens if you press the space bar before Enter while doing Step 3 (via the keyboard entry method). This causes the numerical value to disappear and a solid dimension line to take its place. If you press the space bar a few times, a gap appears where the dimension value should have been. This may be useful if you are unsure of dimensions on an “as built” floor plan and will be taking the plans out into the field to verify them. You can then just write in the values as you measure them.
Baseline Dimensions
These are continuous stacks of dimensions (Figure 6.11).
The baseline dimension, as mentioned before, is very similar in principle to the continuous dimension. The goal is to make a neat stack of evenly spaced dimensions that all start at one point (the base in baseline). To begin, erase the previous continuous dimensions (leaving the squares) and once again draw one linear (horizontal) dimension, as seen before in Figure 6.9.
Step 1. Once you have the squares and one linear dimension, start up the baseline command via any of the preceding methods.
AutoCAD says: Specify a second extension line origin or [Undo/Select]<Select>:
Step 2. A new dimension appears. Pick the next point (corner) along the string of rectangles and click on it (always using OSNAP points, no eyeballing).
AutoCAD says: Dimension text=3.9417
Your value, of course, may be different.
Step 3. You can continue this until you run out of objects to dimension; at that point, just press Esc. Your result is shown in Figure 6.12.
Leader and Multileader
This is an arrow and label combination pointing at something (Figure 6.13).
While a leader is not a true dimension by definition, it is still a very common and necessary member of the dimension family. The values shown by the leader can be not only numerical but also text comments from the designer, concerning the part or object to which it is pointing.
Leaders are so important that AutoCAD has given them a major rework in recent releases. We go over the two main options in increasing order of complexity, starting with the basic leader command, followed by the more feature-rich multileader, with its Add, Remove, Align, and Collect options.
Leader
Step 1. Draw a small box on your screen, making sure Ortho is off. Type in the command leader and press Enter.
AutoCAD says: Specify leader start point:
Step 2. Click with OSNAP precision on your shape, perhaps a midpoint on the top side, as seen in Figure 6.13.
AutoCAD says: Specify next point:
Step 3. Move your mouse at a 45° angle away from the first point and click again at a reasonable distance away. You create the leader line and arrowhead seen in Figure 6.14.
AutoCAD says: Specify next point or [Annotation/Format/Undo]<Annotation>:
Step 4. Turn Ortho back on and draw a short line to the right, clicking when done; this is your horizontal landing, as seen in Figure 6.15.
AutoCAD says: Specify next point or [Annotation/Format/Undo]<Annotation>:
Step 5. You are done, so press Enter.
AutoCAD says: Enter first line of annotation text or<options>:
Type something in, pressing Enter if you wish to do another line, and Enter again if you are done, as seen in Figure 6.16.
Multileader
This method is relatively new and is meant to add more flexibility and usefulness (and inadvertently some complexity) to the leader command. To work with this, you need to bring up the Multileader toolbar, shown in Figure 6.17.
There is something new to the multileader that you did not have with the basic leader. You can set up a multileader style, so all leaders have the exact look you want. In our sample case, we give our multileader a bubble in which to add text. Press the very last button on the right (mleader with a paint brush) and the dialog box shown in Figure 6.18 appears.
Press New… and give the multileader a name, such as Sample Style, and press Continue. You are taken to the Modify Multileader Style dialog box (Figure 6.19). Examine the three tabs, Leader Format, Leader Structure, and Content, carefully. Most of the options are reasonably self-explanatory, and you will see some of them again later on. Under the Content tab, select Multileader type: as Block and Source block: as Detail Callout. Finally, press OK, Set Current, and Close. Now let us try out our new multileader style.
Step 1. Start the multileader command via any of the preceding methods.
AutoCAD says: Specify leader arrowhead location or [leader Landing first/Content first/Options]<Options>:
Step 2. Click anywhere and extend your mouse (Ortho off) at 45° to the right.
AutoCAD says: Specify leader landing location:
Step 3. Click again to place the multileader and bubble. You see something like Figure 6.20.
AutoCAD says: Enter view number<VIEWNUMBER>:
Once you do this, you see the final result (Figure 6.21), the appearance of which can, of course, be fine-tuned.
Now that you have one leader on the screen, it is easy to experiment with other interesting options. Move across the toolbar, starting first with Add Leader (Figure 6.22) and get rid of it via Remove Leader. Then, after adding it back in, create a new set of leaders and line them up using Align Multileaders (Figure 6.23), which aligns the leaders with one that you pick as the primary. Finally, Collect Multileaders (Figure 6.24) combines them into one string.
Secondary Dimensions
It was mentioned that some dimensions are secondary, meaning they are not used as often. We briefly discuss them here, and you may want to also go over them in detail on your own, especially if you feel one or more of them may be extremely useful to your particular field.
Arc length, as you may have guessed, measures the length of an arc. Simply select the toolbar icon and click on the arc you want to measure, as seen in Figure 6.25.
Ordinate dimensions (Figure 6.26) measure horizontal or vertical distances from a datum point (0,0 in this case). They are used in manufacturing to prevent accumulation of errors that can occur using continuous measurements. Draw the shapes shown in Figure 6.26, positioning the lower left corner of the rectangle at 0,0, and begin the ordinate dimension. Then, click major points along the way in either horizontal or vertical directions to get precise values at that location from the origin.
Jogged dimensions are useful when the radius or diameter dimension’s center is off the sheet of paper and cannot be shown directly, so a “break line” of sorts is used. You simply select the arc or circle, then the center location override, and a jogged dimension appears (Figure 6.27).
There are other dimension options we have not yet explored. We come back to them in Level 2. For now, we must move on and learn how to do editing and customizing.
6.3 Editing Dimensions
You should now be quite familiar with the types of dimensions available and how to apply them to basic shapes. The next step is to be able to edit them or change their values, if needed. This is a very simple and short topic.
You already learned that you can edit text and mtext by double-clicking on it. The text in the dimensions is essentially editable mtext, so go ahead and double-click any part of the dimension to edit it. Recall also, in Chapter 4, we covered ddedit and mentioned it was also useful for editing purposes. You can use that command as well, and indeed with AutoCAD versions prior to 2013, you need to use ddedit, as double-clicking on the dimension brings up the Properties palette. The “issue” was resolved for this release.
What happens next depends on whether you have the Ribbon on your screen or not. If you do not, then you see the basic mtext editor, as in Figure 6.28. You can just edit the value and press OK. If you do have the Ribbon active, then the editing field appears but not the rest of the mtext editor, with the Ribbon’s Text Editor tab highlighted instead.
Here is a useful tip. If you want to reset your forced dimension value back to its natural value and you forgot what that was, just type in<>. These two “alligator teeth” brackets restore the natural value. Type them in instead of the forced value and click on OK. Try it yourself.
6.4 Customizing Dimensions
We have one more topic to cover on our way to basic proficiency in dimensioning. It is customization; and as mentioned at the start of the chapter, it is an extensive subject, necessitating it being split into the fundamentals here and advanced customization in Chapter 13. The goal here is to learn what experience has shown to be the most important four customization tools. This allows you to be productive in most of the drafting situations you are likely to encounter as a beginner. Later, you will add to this knowledge by learning tools used by CAD administrators and senior designers.
So, what customization is necessary at this level? We need to learn how to:
Change the units of the dimensions.
Change the font of the dimensions.
To be able to change any of these, we need to introduce a new tool, the Dimension Style Manager dialog box, or dimstyle for short. There, you find a button to bring up the Modify Dimension Style dialog box. It is a “one-stop-shopping” dialog box for dimension modification that you will eventually need to learn backward and forward.
Dimstyle
Using any of the preceding methods, bring up the Dimension Style Manager, as seen in Figure 6.29.
The Dimension Style Manager dialog box has some options for creating a new dimension style or just modifying an existing one. For us at this point, it really does not matter which we pick, so just press Modify….
You then are taken to the Modify Dimension Style dialog box, shown in Figure 6.30. Note that you may not necessarily see the Lines tab as the open tab, as seen in Figure 6.30. If you do not, just click on it to have the same thing on your screen as what is in the text.
This rather imposing dialog box contains tools to significantly modify any dimension. We, in fact, do so in Chapter 13, as we explore nearly every feature. For now, we just want to focus on learning how to modify the handful of items shown in the bulleted list at the start of Section 6.4.
Step 1. Change the Units of the Dimensions
Pick the Primary Units tab and simply select the drop-down menu at the very top left, where it says Unit format:. The default value is Decimal; change it to Architectural and select the appropriate Precision in the menu just below it (the default value is fine). That is all we need from that tab for now. Notice how the preview window on the upper right reflects your choice of units, as seen in Figure 6.31.
Step 2. Change the Font of the Dimensions
To do this you need to click on the Text tab. You then see Text style: on the upper left. If you just opened a new AutoCAD file to practice dimensions, you probably do not have a font set and get only Standard as your choice if you click the down arrow. Fortunately, Standard is now a more attractive Arial font, not the stick-figure Simplex it used to be, so changing fonts is optional but still useful to know. For example, the RomanS font is a popular alternative.
Something else to keep in mind is that, in a real working drawing, you would likely set your text style before you work on any dimensions (an important point, take note). Then, you would just select the font from the list. The idea here is to match up your regular font used in text and mtext with the font used in dimensioning, another important point. In general, you should stick to one font in a given drawing and just vary the size as needed. The title block is exempt from this, as that may have special fonts, logos, and the like.
AutoCAD, of course, anticipates that you may not have set a font style when you first set up dimensions and allows you to do this from the Text tab by bringing up the Style box when you click the button just to the right of the Text style menu (with the three dots, …). Go ahead and set a different font if you wish, RomanS 0.25" perhaps, and the new setting appears, as seen in Figure 6.32.
Step 3. Change the Arrowheads of the Dimensions
The default for all dimensioning is the standard arrowhead. You can easily change that to any other type, including the Architectural tick, popular with architects. You can even create a custom arrowhead (not something we try to do here).
Click over to the Symbols and Arrows tab. In the upper left corner under the Arrowheads section, you see First:. That is the first arrowhead type, and if you change it, AutoCAD assumes you want the second one to be the same and changes it as well. Simply click the down arrow and select the Architectural tick. Leave everything else the same. The result is shown in Figure 6.33.
Step 4. Change the Fit (Size) of the Dimensions
This function is quite important. Located in the Fit tab, just underneath the preview window, it features only a few lines and is shown in Figure 6.34.
The idea here is to increase the size of the dimensions proportionately, so everything scales up evenly and smoothly in step with the size and scale of your overall drawing. This concept, however, opens up a number of questions. Chief among them: What value do you enter into there and why? We are not ready to discuss this yet, but we do in Chapter 10 (on paper space). So, for now, do not enter in anything but be aware of how to do it when needed. When you get to dimensioning the floor plan in the next section, enter 15 in that space.
This is it for now; just click on OK and AutoCAD returns you to the Dimension Style Manager, where you can just press Close. Try creating a dimension and see what it looks like now. Figure 6.35 shows a set of horizontal dimensions before the changes we just went through and another one afterward. The difference is obvious. For now, this is all you need to make professional-looking dimensions. Review and memorize everything you learned and go on to the floor plan in Figure 6.36, adding dimensions to complete the drawing.
6.5 In-Class Drawing Project: Adding Dimensions to Floor Plan Layout
Let us now apply what we learned to the floor plan. Open the file and freeze all the layers except the walls and windows. If you really want to get fancy, put the wall solid hatch on its own (visible) layer and freeze the regular floor hatch layer so the carpeting and floors do not show. Next create a new layer for the dimensions, A-Dim. Finally, set up the dimensions: Use Architectural units and Arial 6" font, leave the arrowheads as they are, and change the scale under the Fit tab to 15. Dimension the floor plan any way you want; what is shown in Figure 6.36 is a guide but not the only way to do it. Note that the outer dimensions are continuous.
Summary
You should understand and know how to use the following concepts and commands before moving on to Chapter 7:
Exercises
1. Retrieve Exercises 2, 3, 4, and 6 from Chapter 3 and set up and add all shown dimensions. (Difficulty level: Easy; Time to completion: 10–15 minutes.)
2. Retrieve Exercises 4, 5, and 6 from Chapter 4 and set up and add all shown dimensions. (Difficulty level: Easy; Time to completion: 10 minutes.)
3. Retrieve Exercises 3 and 4 from Chapter 5 and set up and add all shown dimensions. (Difficulty level: Easy; Time to completion:<10 minutes.)
4. In a new file, set up the appropriate layer, colors, and linetypes. Then, draw and fully dimension the following mechanical part. Select Decimal as the dimstyle, with precision of 0.00 and inch symbols (") for a suffix. (Difficulty level: Easy/Moderate; Time to completion: 35–45 minutes.)
5. In a new file, set up the appropriate layer, colors, and linetypes. Then, draw and fully dimension the following mechanical plate. Select Decimal as the dimstyle, with precision of 0.00 and inch symbols (") for a suffix. Make careful use of mirror to minimize redundant work. All sizing is based on the smallest two circles and their position from an arbitrary centerline. (Difficulty level: Moderate; Time to completion: 35–45 minutes.)
6. In a new file, set up the appropriate layer, colors, and linetypes. Then, draw and fully dimension the following mechanical part. Select Decimal as the dimstyle, with precision of 0.00 and inch symbols (") for a suffix. (Difficulty level: Moderate; Time to completion: 35–45 minutes.)
7. In a new file, set up the appropriate layer, colors, and linetypes. Then, draw and fully dimension the slightly simplified version of the bolt assembly seen on the opening of this chapter. Select Decimal as the dimstyle, with precision of 0.00 and inch symbols (") for a suffix. Note that no dimensions are available for some internal parts of the bolt; you have to improvise. (Difficulty level: Moderate/Advanced; Time to completion: 60 minutes.)
