The Lines tab contains controls for dimension lines and extension lines. I think the existing settings create dimensions that are too crowded. To allow placement of more dimensions without as much clutter, make the following changes to settings on the Lines tab, as shown in Figure 4.3:

Figure 4.2. Changing name of dimension style

Figure 4.3. Lines tab

The Symbols And Arrows tab controls dimension features that used to be in the Lines And Arrows tab. To control the appearance of arrowheads and center marks, I recommend the changes shown in Figure 4.4:

Setting the center-mark style to Line allows you to use the DIMCENTER (DCE) command to quickly place proper center marks. This is the equivalent of setting a negative value for the variable DIMCEN. Later, in the section "Child Variations: Radial and Diameter," I'll recommend that you set this value to None for styles used for diameters and radii.

The Text tab controls the style, appearance, and position of text. I recommend the following changes, as shown in Figure 4.5:

Figure 4.4. Symbols And Arrows tab

Figure 4.5. Text tab

Set the text style to one that's based on an acceptable font. Only one font that ships with AutoCAD meets all standards of technical graphics: romans.shx. Some offices use others, including arial.ttf, which I use for illustrations that I plan to put into another document. Whatever font your style is based on, don't name that style Standard. (I use the font name as the style name.)

If you haven't yet created a text style, click the button with the three dots (the ellipses, ...) next to the Text Style drop-down list. The Text Style dialog box opens. Create a new style based on the romans.shx font with a height of 0, and close the dialog box. Now, select your new style from the drop-down list.

A text height of 0.125 meets ASME standards, and changing Offset From Dim Line to 0.04 makes it more likely that a dimension will fit inside the extension lines.

The Fit tab controls the manner in which AutoCAD places dimensions and text, as well as the important scaling factor used for all dimension features. Set the Fit tab settings to those illustrated in Figure 4.6. Here are the specifics:

Figure 4.6. Fit tab

You normally move the dimension arrows outside of extension lines when there isn't room for both text and arrows, so select Arrows in the Fit Options. However, you may encounter a situation where either Both Text And Arrows or Always Keep Text Between Ext Lines works better. If your dimensions don't appear where you want them automatically, try one of those two settings and see if the situation improves.

Select Scale Dimensions To Layout so dimensions are a consistent size when plotting (as discussed in greater detail in Chapter 6, "Plotting"). Selecting Scale Dimensions To Layout requires that you use layouts correctly.

The Primary Units tab includes the same kinds of controls found in the Drawing Units dialog box. You don't have to use the same settings in both places. Figure 4.7 demonstrates the settings I recommend on the Primary Units tab:

Changes in this tab depend on your application. In the U.S., the number of decimal places used on a mechanical drawing indicates a tolerance as defined in the title block. Don't use too many decimal places, because doing so implies a closer, and much more expensive, tolerance for each dimension. Set the number of decimal places only to what you need—I use three for a general style, and four for mechanical parts where classes of fits or tool-room tolerances are being used. Precision for individual dimensions can be changed to reflect a greater or lesser tolerance.

The Alternate Units tab was added to AutoCAD at a time when dual dimensions—inches and millimeters—were often used for international customers; however, the current ASME standard is to use either inches or millimeters for dimensions, but not both. In other words, the Alternate Units tab isn't used much these days. In fact, DOD-STD-1476 prohibits dual dimensions on military drawings. If for some reason you must place dual dimensions, you should know about two ways to convert dimensions from inches—hard conversions and soft conversions

A hard conversion is the result of multiplying one value by its exact conversion factor to get the other value. In converting metric to inches, this would mean multiplying all dimensions by 25.4. The result is exact, but it may appear very unusual to those who normally use the alternative units. A value of 3.375″ would be common in the U.S., but its hard conversion to 85.725mm would be unusual to those designing in millimeters. Likewise, a conversion from 1420mm to 55 29/32″ would seem odd to someone who normally uses fractional inches.

A soft conversion is only used when a hard conversion isn't necessary. In a soft conversion one value is close to, but not exactly the same as, the other, but both are common values in each system. Although .125″ may be 3.175mm when a hard conversion is used, a soft conversion of 3mm is close enough for things like text height.

Use the following settings for hard conversions, after checking the Display alternative units box in the upper left corner of the tab:

If you want soft conversions for placing dual dimensions, use these settings:

Generally, it's easier to read dual-dimensions on parts when one value is displayed over the other, so I also suggest selecting Below Primary Value under Placement.

Here are my recommendations:

Figure 4.8. Alternative Units Tab

Figure 4.9. Tolerances Tab

If you use tolerances on individual dimensions, try creating a separate dimension style called Decimal-inch-tol for doing those dimensions. I also suggest changing the method to Limits. It takes up less room than the other methods, and most machinists prefer limit tolerances, in my experience.

The reason I'd leave the upper and lower tolerance values at 0 is that they can be changed individually using the Properties palette. This kind of tolerance is generally used for precision fits, so the upper and lower tolerances are different for each dimension. Note the recommendation in Chapter 1, "AutoCAD Productivity," that you create geometry to Maximum Material Condition. If you follow that advice, one of the limits is always zero, depending on the type of feature being dimensioned.

Once you've created a basic dimension style, you can add variations that apply only to certain kinds of dimensions. These are known as child styles; they're associated with a parent style and start with all the same settings as the parent style. These variations let you fine-tune a dimension style.

To add child styles, click the OK button at the bottom of the Modify Dimension Style dialog box, and return to the Dimension Style Manager. Click the New button, and then select Radius Dimensions under Use For, as shown in Figure 4.10. Click Continue, and make the following changes for radius dimensions.

Now do the same thing for diameter dimensions. When you're done, you have a new style with two child variations that will work for most mechanical dimensions (see Figure 4.11).

These child variations let you add radius and diameter dimensions without center marks. You prevent a center mark from being part of the block that defines a radial or diameter dimension. If you use DIMCENTER (DCE) to add center marks only when you need them, they have extensions that you can delete without exploding the dimension. In the example shown in Figure 4.12, I added center marks independently and then placed radial and diameter dimensions directly, without any post-placement editing.

Figure 4.10. Radius variations

Figure 4.11. Child styles

Figure 4.12. Using child styles

The spacing of dimension lines and the appearance of extension lines are controlled in the Lines tab. To allow placement of dimensions without as much clutter, I recommend the following changes, as shown in Figure 4.14:

Figure 4.14. Lines tab: Architectural

I suggest that you set the values controlled in the Symbols And Arrows tab to the same settings as those for mechanical. I recommend the following changes, as shown in Figure 4.15:

Fonts with a .shx extension are vector-based fonts that come with AutoCAD. Fonts with a .ttf extension are Windows system fonts that may or may not be available on any given Windows computer. (See the "Text Styles" section for the solution to that problem.) Therefore, I normally use romans.shx, which is an acceptable font for architectural drawings but doesn't look as stylish as most offices like. You may want to use the cityblueprint.ttf font, which I find the more readable of the two blueprint fonts (countryblueprint.ttf is the other). Most offices have both those fonts on their workstations. If you send drawings to other offices, avoid any specialty third-party fonts that don't come with AutoCAD, or use eTransmit to package the fonts with the drawings when you send them.

I recommend the following changes, as shown in Figure 4.16:

Figure 4.15. Symbols And Arrows tab: Architectural

Figure 4.16. Text tab: Architectural

Because the parent style controls only angles, radii, and diameters, leave Text Alignment as Horizontal, and define a child linear style for dimensions that are to be aligned and centered.

There isn't much to change for the Fit tab in architectural dimensions, but the controls in the Fit tab can cause all kinds of placement problems later. Figure 4.17 shows three settings I always change:

Figure 4.17. Fit tab: Architectural

The Fit tab controls the manner in which AutoCAD fits the text and arrows for dimensions into the space available. You normally move the arrows outside of extension lines when there isn't room for both text and arrows, so select Arrows under Fit Options. However, in some situations, either Both Text And Arrows or Always Keep Text Between Extension Lines works better. If your dimensions don't appear where you want them automatically, try one of those two settings and see if the situation improves.

When dimensions are too small to fit between extension lines, I like to have them connected to their proper location with a leader. Select Scale Dimensions To Layout so dimensions are a consistent size when plotting. Selecting Scale Dimensions To Layout requires that you use layouts correctly. See Chapter 6 for information on plotting.

The Primary Units tab is where architectural dimensions become architectural. Figure 4.18 shows at least one recommendation that may surprise you:

I remind you that the value set in the Drawing Units dialog box isn't used for dimensions. You must set dimension units here. Why the 1/256″ precision? I set the precision to the smallest possible value; that way, any drawing errors show up as I add dimensions. If I make no mistakes creating the geometry, I don't ever see a fraction smaller than ¼″ in a dimension.

I find that setting fractions to Diagonal is easiest for me to read, and suppressing 0 feet, but not 0 inches, helps fit text into smaller spaces between extension lines while clarifying that some dimensions really are in whole feet.

Figure 4.18. Primary Units tab: Architectural

Unless you want to add dual dimensions to a drawing that will be used in another country, there's no reason to change any settings in the Alternate Units tab. Tolerances aren't generally used in architectural drawings, so there is no reason to change the Tolerances tab either.

Child variations let you define a single parent style that controls almost all dimension features for most types of dimensions and then customize the appearance of other types. Because I like using horizontal dimensions for radius, angular, and diameter dimensions, I use a child variation to make linear dimensions look right.

To create a child variation, do the following (see Figure 4.19):

Figure 4.19. Linear child variation

Under the Symbols And Arrows tab, change the following (see Figure 4.20):

Figure 4.20. Symbols And Arrows tab: Linear

Under the Text tab, change the following (see Figure 4.21):

When placing linear dimensions in small areas, AutoCAD often leaves out the dimension lines—even though they may fit between extension lines—unless you check Draw Dim Line Between Ext Lines.

Figure 4.21. Text tab: Linear

Figure 4.22. Fit tab: Linear

To set up child variations for radial dimensions, click OK to close the Modify Dimension Style dialog and then do the following:

Repeat these steps to create a child dimension style for diameter dimensions. The result looks like Figure 4.23 when you list dimension styles in the Dimension Style Manager dialog box.

Figure 4.23. Architectural style with child variations

The Lines tab offers the most significant changes for civil engineering and surveying drawings. Recommended changes are shown in Figure 4.24:

Figure 4.24. Lines tab

The key change in the Text tab is the placement of the text so that it aligns with property lines. Figure 4.25 shows the changes listed here:

The Fit tab has only two recommended changes:

Figure 4.25. Text tab: Civil

The Scale Dimensions To Layout option shown in Figure 4.26 is the important one here. Note that the scale factors you use in floating viewports when you set up a layout are affected by the use of feet as the basic unit. Because the paper is measured in inches and the geometry is measured in feet, the scale factor used for the viewport is 1/12 the actual plotted scale. This means that a scale of 1:200 for the viewport appears as 1″=200′ in the title block.

The Primary Units tab uses the default decimal units because you'll be drawing in decimal feet. The other changes I recommend are shown in Figure 4.27:

Figure 4.26. Fit tab: Civil

Figure 4.27. Primary Units tab: Civil

Civil and surveying drawings generally use decimal feet, but I occasionally run across someone using engineering units for a civil drawing to make it compatible with architectural drawings that will be used as external references. One user tried adding dimensions in decimal feet, but the values were 12 times too large. I suggested converting inches into feet by placing 1/12 as a scale factor in the Measurement Scale area of the Primary Units tab. This multiplied each dimension by 1/12 (0.0833333), converting inch units to feet.

When you place dimensions for boundary lines, do the following:

The result is a dimension in decimal feet over the boundary line.

I use this system frequently on nautical charts for course lines. To place the correct angle without having to type values like N34°15′25″E all the time, follow these steps:

The AutoCAD Help system identifies the wildcards shown in Table 4.3 that can be used when identifying layer names. See how helpful the Help system is?

Commercial construction projects commonly employ a separate drawing file for each floor or level of a building. When it becomes necessary to compare two or more levels, drawings are externally referenced into a single file. The American Institute of Architects (AIA) has developed layer standards for use in commercial projects. The complete AIA layer standard is lengthy, and you'll have to purchase it if you want a copy for your office. In the meantime, here's my summary of the naming conventions from the AIA publication "CAD Layer Guidelines" (1990, updated 1999).

Layer names must be composed of up to four fields, each separated by a dash as follows: X-XXXX-XXXX-XXXX. The first field requires a single character, and the other fields require four characters. Not all layer names have all four fields, but where multiple fields are used, each subsequent field modifies the field immediately preceding it. The shortest possible standard layer name is 6 characters; the longest is 16.

For example, the layer name A-WALL-DIMS-NEWW identifies the discipline, which in this case is architectural; the major group, which in this case is walls; the minor group, which in this case is dimensions; and the status of the objects being referenced, which in this case is new construction. Users can add minor categories, and the status field is always optional. The following summary shows some of the field names used in each category. Discipline groups are listed in Table 4.4.

Each discipline group can be modified by a second field that indicates the types of objects placed on that layer. Those four-character fields are shown in Table 4.5.

A third field further defines the objects identified in Field 2, indicating the types of objects that are placed on those layers as modifiers. Examples are shown in Table 4.6.

The final field is a status field, indicating whether the objects shown are to be demolished, represent existing structures that won't be demolished, are new structures, and so on. Table 4.7 lists the four-character status codes.

For more information about the AIA layer-naming guidelines, or to purchase the guidelines, see the AIA website: http://www.AIA.org.

You may find the AIA guidelines cumbersome in residential design. When designing or drawing a single-family residence, I prefer to have all floors in one file and use the following layer-naming system. Like the system developed by the AIA, it uses separate fields, but I use three characters in each rather than four. I present it here as an example of how you may construct your own layer-naming standard independent of the AIA standards.

Some layers have single fields, but most are associated with a floor or level. The four standard fields I use to represent levels are FND (foundation), FL1 (first floor), FL2 (second floor), and ROF (roof). I use the second field to represent the linetype or type of object: OBJ (object), HID (hidden lines), ELE (electrical), and so on. This system may not work for you, but it simplifies things for me. Table 4.8 provides some suggested layer-name fields.

If an organization has developed layer-naming guidelines for mechanical design, I haven't heard of it. When creating drawings of parts for use in an assembly drawing, I resort to the basic layer names shown in Table 4.9, with as many part-specific names as necessary. The fields identified as PT1, and so on, are given a specific part name.