AutoCAD 2005 for Dummies

AutoCAD displays coordinates and linear measurements.

  The precision setting controls how precisely AutoCAD displays coordinates, distances, and prompts in some dialog boxes. In particular, the Coordinates box on the status bar displays the current cursor coordinates using the current precision. A grosser — that is, less precise — precision setting makes the numbers displayed in the status bar more readable and less jumpy. So be gross for now; you can always act a little less gross later.

  The linear and angular precision settings only affect AutoCAD’s display of coordinates, distances, and angles on the status bar, in dialog boxes, and in the command line area. For drawings stored as DWG files, AutoCAD always uses maximum precision to store the locations and sizes of all objects that you draw. In addition, AutoCAD provides separate settings for controlling the precision of dimension text — see Chapter 10 for details. 

4. Choose an angular unit type from the Angle Type drop-down list.

Decimal Degrees and Deg/Min/Sec are the most common choices.

The Clockwise check box and the Direction button provide additional angle measurement options, but you’ll rarely need to change the default settings: Measure angles counterclockwise and use east as the 0 degree direction. 

5. From the Angle Precision drop-down list, choose the degree of precision you want when AutoCAD displays angular measurements. 

6. In the Drag-and-Drop Scale area, choose the units of measurement for this drawing.

Choose your base unit for this drawing — that is, the real-world distance represented by one AutoCAD unit. 

7. Click OK to exit the dialog box and save your settings.

Telling your drawing its limits

The next model space setup task is to set your drawing’s limits. You wouldn’t want it staying out all night and hanging out with just anybody, would you? The limits represent the rectangular working area that you’ll draw on, which usually corresponds to the paper size. Setting limits correctly gives you the following advantages:

? When you turn on the grid (described in the section, “Making the drawing snap-py (and grid-dy),” later in this chapter), the grid displays in the rectangular limits area. With the grid on and the limits set correctly, you always see the working area that corresponds to what you’ll eventually be plotting, so you won’t accidentally color outside the lines.

? The ZOOM command’s All option zooms to the greater of the limits or the drawing extents. (The extents of a drawing consist of a rectangular area just large enough to include all the objects in the drawing.) When you set limits properly and color within the lines, ZOOM All gives you a quick way to zoom to your working area.

? If you plot from model space, you can choose to plot the limits area. This option gives you a quick, reliable way to plot your drawing, but only if you’ve set limits correctly!

  Many CAD drafters don’t set limits properly in their drawings. After you read this section, you can smugly tell them why they should and how.

  You can start the LIMITS command from a menu choice, but all subsequent action takes place on the command line; despite the importance of the topic, AutoCAD has no dialog box for setting limits.

The following procedure shows you how to set your drawing limits:

1. Choose Format>Drawing Limits from the menu bar to start the LIMITS command; or type LIMITS on the command line and press Enter.

The LIMITS command appears on the command line, and the command line displays the following prompt at the bottom of the screen:

Command: limits
Reset Model space limits:
Specify lower left corner or [ON/OFF] 0.000,0.0000:

The value at the end of the last line of the prompt is the default value for the lower-left corner of the drawing limits. It appears according to the units and precision that you selected in the Drawing Units dialog box — for example, 0’–0” if you selected Architectural units with precision to the nearest inch.

2. Type the lower-left corner of the limits you want to use and press Enter.

The usual value to enter at this point is 0,0. (Type a zero, a comma, and then another zero, with no spaces.) You can just press Enter to accept the default value.

AutoCAD now prompts you for the upper-right corner of the limits:

Specify upper right corner 12.0000,9.0000:

The initial units offered by AutoCAD correspond to an architectural A size sheet of paper in landscape orientation. (Almost no one uses Architectural A size paper; here’s a classic example of a programmer choosing a silly default that no one has bothered to change in 22 years!)

3. Type the upper-right corner of the limits you want to use and press Enter.

You calculate the usual setting for the limits upper-right corner by multiplying the paper dimensions by the drawing scale factor. For example, if you’re setting up a ?”=1’–0” drawing (drawing scale factor=96) to be plotted on a 24?36-inch sheet in landscape orientation, the upper-right corner of the limits should be 36 inches times 96, 24 inches times 96. Okay, pencils down. The correct answer is 3456,2304 (or 288 feet,192 feet).

  Alternatively, you can cheat when specifying limits and read the limits from the tables on the Cheat Sheet.

If you have the grid turned on, AutoCAD redisplays it in the new limits area after you press Enter.

  If you’re using Architectural or Engineering units and you want to enter measurements in feet and not inches, you must add the foot designator after the number, such as 6’; otherwise, AutoCAD assumes that you mean inches. 

4. Choose View>Zoom>All.

AutoCAD zooms to the new limits.

Making the drawing area snap-py (and grid-dy)

AutoCAD’s grid is a set of evenly spaced, visible dots that serve as a visual distance reference. (As I describe in “Telling your drawing its limits,” earlier in this section, the grid also indicates how far the drawing limits extend.) AutoCAD’s snap feature creates a set of evenly spaced, invisible hot spots, which makes the cursor move in nice, even increments. Both grid and snap are like the intersection points of the lines on a piece of grid paper, but grid is simply a visual reference, whereas snap constrains the points that you can pick with the mouse. You can — and usually will — set the grid and snap spacing to different distances.

Set the grid and the snap intervals in the Drafting Settings dialog box with these steps: 

1. Right-click the Snap or Grid button in the status bar and choose Settings.

The Drafting Settings dialog box appears with the Snap and Grid tab selected, as shown in Figure 3-6.

Figure 3-6: Get your Drafting Settings here!

The Snap and Grid tab has four parts, but the Snap and Grid sections are all you need to worry about for most drafting work.

2. Select the Snap On check box to turn on snap.

This action creates default snaps half a unit apart.

3. Enter the Snap X Spacing for the snap interval in the accompanying text box.

Use the information in the sections preceding this procedure to decide on a reasonable snap spacing.

The Y spacing automatically changes to equal the X spacing, which is almost always what you want. 

4. Select the Grid On check box to turn on the grid. 

5. Enter the Grid X Spacing for the grid in the accompanying text box.

Use the information in the sections preceding this procedure to decide on a reasonable grid spacing.

The Y spacing automatically changes to equal the X spacing. As with the snap spacing, you usually want to