4 Little-Known AutoCAD Dimensioning Tips
Jaiprakash Pandey posted on July 07, 2016 |
Learn about 4 little-known but useful dimensioning tips like adding tolerances, feature control fram...

Dimensioning and annotations are indispensable parts of AutoCAD drawings. Every AutoCAD user is well aware of dimensioning tools, but there are some features in AutoCAD dimensioning that are mostly overlooked or used rarely despite their great applications. In this article, I will list four such useful but lesser-known features of AutoCAD dimensioning.

Adding Tolerances in Dimensions

For adding tolerance in AutoCAD dimensions, you can create a new dimension style with tolerance values and settings. This dimension style containing tolerance values can be applied wherever tolerances are required. 

To make a dimension style with tolerances, type “D” or “DIMSTYLE” on the command line and press Enter. The Dimension Style Manger window will pop up. Click on the New button from this window, give your new dimension style a name and click on the Continue button. For example, I will name this dimension style “Tolerance Dim.”

A new Dimension Style window will pop up. Select the Tolerances tab from this window. You will notice that all settings related to tolerances can be found on this tab. Let’s assume that we want to create a dimension with a “Deviation” tolerance format as shown in Figure 1. 

Figure 1. Dimension with a “Deviation” tolerance format.
Figure 1. Dimension with a “Deviation” tolerance format.

This type of tolerance is called deviation type because the upper and lower limits of tolerance are different. To create this tolerance type, select Deviation from the Method drop-down menu of the Tolerance format panel. Select a precision of 0.00 and specify the upper and lower limits of tolerance in the specified fields. Keep all settings unchanged and click on OK to apply these settings. See Figure 2 for reference.

Figure 2. Modify Dimension Style window.
Figure 2. Modify Dimension Style window.

Now, select our previously created Tolerance Dim as the current dimension style and create any type of dimension, such as linear, angular or aligned, in the drawing area. You will notice that the dimension will accompany a tolerance value that you specified earlier in the Dimension Style window. 

To create a normal dimension without any tolerance values, change your dimension style to the default style.

Adding a Feature Control Frame

In mechanical drawings, tolerance is added in the symbolic language of geometric dimensioning and tolerancing (GD&T), where different types of tolerances are specified with symbols and enclosed within feature control frames that accompany the dimensions. By using this method, lots of information can be easily squeezed into a small space with the help of a few symbols.

To add tolerances into a dimension with the help of a feature control frame, you first need to create a base dimension. Let’s take an example of a dimension with a defined position tolerance as shown in Figure 3.

Figure 3. Dimension with position tolerance defined using the feature control frame.
Figure 3. Dimension with position tolerance defined using the feature control frame.

Here, the symbols indicate that the associated dimension has a tolerance related to its true position and the tolerance zone is cylindrical. The tolerance value is 0.02 at the maximum material condition with respect to primary datum A and secondary datum B. 

To add this feature control frame, expand the Dimensions panel on the Annotate tab and click on the tolerance symbol. You can also use its command equivalent, “TOL.”

A Geometric Tolerance window will pop up with lots of boxes. Click on the first box in the Sym panel and select the type of tolerance from 14 tolerance types. Now, click on the first box of the Tolerance 1 panel. A “Ø” symbol will be added, indicating the cylindrical tolerance zone. In the next field, enter the value of tolerance, then click on the box next to the tolerance value and select the material condition modifier. In the example above, “M” enclosed in a circle indicates maximum material condition. In the datum 1 and datum 2 fields, enter A and B respectively—this will indicate primary and secondary datum features in your feature control frame. See Figure 4 for reference. 

Figure 4. Geometric Tolerance window.
Figure 4. Geometric Tolerance window.
When these settings are done, click on OK and place your feature control frame close to its associated dimension.

Adding Dual Dimensioning

Dual dimensioning is used when you want to specify dimensions in two different units. Let’s say that you want to specify the length in inches as well as in millimeters for your drawing using the same dimension. For that, you can make use of dual dimensioning. In this case, a new dimension style also needs to be created and this dimension style can be used whenever dual dimensioning is required. 

Type “D” on the command line and press Enter to open the Dimension Style Manager. Select the dimension style that you want to modify and click on the Modify button from the Dimension Style Manager window. Select the Alternate Units tab from the Modify Dimension Style window. You will notice that all options in this tab are inactive. Click on the “Display alternate units” radio button on the upper-left corner of the tab. Select “Unit format” from the drop-down menu and specify the precision of alternate units. 

To make this alternate unit useful, you need to specify the multiplier. The multiplier will decide the output of the alternate unit based on the value of the primary unit. As an example, let’s assume that the primary unit in our drawing is in inches and that we want to specify alternate units in millimeters. For that, the multiplier unit is 25.4 because 1 in is equal to 25.4 mm. Type “25.4” in the “Multiplier for alt units” field and click on OK when you have made all of these changes.

Figure 5. An example of dual dimensioning with tolerance.
Figure 5. An example of dual dimensioning with tolerance.

Now use this dimension style to create a dimension with primary as well as alternate units. An example of an alternate unit is shown in Figure 5. In this case, dimensions in the primary unit are in inches. The tolerance is also in inches for the primary unit. In the alternate unit, the dimension and tolerances are in millimeters.

Making a Custom Arrow Style for Dimensions

AutoCAD has many dimensioning arrow styles, but if you want to include a custom arrow style for all your dimensioning needs, you can create one using blocks. To make an arrow style, use the draw and modify tools and then convert the drawing into a block. Make sure you convert this geometry into a simple block and not an annotative block, because annotative blocks cannot be used for making custom arrows. Let’s name this block “Custom arrow.” For this example, I am making an arrow style that looks like this:

Figure 6. Custom arrow style.
Figure 6. Custom arrow style.

You should also make sure to use the pointed nose of this geometry as the base point to keep the arrow properly aligned with respect to dimensions. Now open the Dimension Style Manager and select the dimension style that you want to modify. Then, click on the Modify button. From the Modify Dimension Style window, select the Symbols and Arrows tab, click on the Arrowheads drop-down menu and select User Arrow. From the next drop-down menu, select “Custom arrow block” and click on the OK button. Click on OK again to close the Dimension Style Manager window.

Now you can use this modified dimension style whenever you need a custom arrow. I used the modified dimension style with my custom arrow and this is the result:

Figure 7. Dimensions with custom arrow.
Figure 7. Dimensions with custom arrow.

Did you find these tips useful? Which one is your favorite feature of AutoCAD dimensioning? Tell us in the comments below.

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