Making the Most of Model Space

After you've decided on drawing scale and sheet size, you're ready to set up your drawing. Most drawings require a two-part setup:

1. Set up model space, where you'll create most of your drawing.
2. Create one or more paper space layouts for plotting.

As I explain in Chapter 2, model space is the infinitely large, three-dimensional environment in which you create the “real” objects you're drawing. You can set up your model space as described in this section; Chapter 5 introduces you to setting up your paper space layouts.

Setting your units

First, set the linear and angular units that you want to use in your new drawing. The following procedure describes how:

1. Click the Application button and then choose Units from the Drawing Utilities group.

   The Drawing Units dialog box appears, as shown in Figure 4-4.

   

   Figure 4-4: Set your units here.

2. Choose a linear unit type from the Length Type drop-down list.

   Choose the type of unit representation that's appropriate for your work. Engineering and Architectural units are displayed in feet and inches; the other types of units aren't tied to any particular unit of measurement. You decide whether each unit represents a millimeter, centimeter, meter, inch, foot, or something else. Your choice is much simpler if you're working in metric: Choose Decimal units.

   AutoCAD can think in inches! If you're using Engineering or Architectural units (feet and inches), AutoCAD interprets any distance or coordinate you enter as that many inches. You must use the ' (apostrophe) character on your keyboard to indicate a number in feet instead of inches.

3. From the Length Precision drop-down list, choose the level of precision you want when AutoCAD displays coordinates and linear measurements.

   The Length Precision setting controls how precisely AutoCAD displays coordinates, distances, and prompts in some dialog boxes. For example, the Coordinates section of the status bar displays the current coordinates of the crosshairs using the current precision.

   The linear and angular precision settings affect only AutoCAD's display of coordinates, distances, and angles on the status bar, in dialog boxes, and in the command window and Dynamic Input tooltip areas. For drawings stored as DWG files, AutoCAD always uses maximum precision to store the locations and sizes of all objects that you draw, regardless of how many decimal places you choose to display in the Drawing Units dialog box. In addition, AutoCAD provides separate settings for controlling the precision of dimension text — see Chapter 14 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: Unless you're a land surveyor, 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 Insertion 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.

   The AutoCAD (but not the AutoCAD LT) Drawing Units dialog box includes a Lighting area where you specify the unit type to be used to measure the intensity of photometric lights. I introduce lighting as part of rendering 3D models in Chapter 23.

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

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

For the last three decades, AutoCAD's grid consisted of a set of evenly-spaced dots that served as a visual distance reference. You can still configure a dot grid in AutoCAD 2012, but starting with AutoCAD 2011, the default is a snazzy graph-paper-like grid made up of a network of lines.

AutoCAD's snap feature creates a set of evenly spaced, invisible hot spots, which make the crosshairs move in nice, even increments as you specify points in the drawing. Both Grid Mode and Snap Mode are like the intersection points of the lines on a piece of grid paper, but the grid is simply a visual reference — it never prints — whereas Snap constrains the points that you can pick with the mouse. You can — and usually will — set grid and snap spacing to different values.

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

1. Right-click the Snap Mode or Grid Display button on the status bar and choose Settings.

   The Drafting Settings dialog box appears with the Snap and Grid tab selected, as shown in Figure 4-5.

   The Snap and Grid tab has six sections, but the Snap Spacing and Grid Spacing areas within that tab are all you need to worry about for most 2D drafting work.

   

   Figure 4-5: Get your drafting settings here!

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

   This action enables default snaps half a unit apart (ten units apart if you're working with the default metric template).

   AutoCAD usually has several ways of doing things. You can also click the Snap Mode button on the status bar to toggle snap on and off; the same goes for the Grid Display button and the grid setting. Or you could use the function keys: F7 toggles the grid off and on, and F9 does the same for Snap Mode.

3. Enter the snap interval you want in the Snap X Spacing box.

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

   If the Equal X and Y Spacing check box is selected, the Y spacing changes automatically to equal the X spacing, which is almost always what you want. Uncheck the box if you want to specify unequal snap spacing.

4. Select the Grid On check box to turn on the grid.
5. Enter the desired grid spacing in the Grid X Spacing box.

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

   As with snap spacing, if the Equal X and Y Spacing check box is selected, the Y spacing automatically changes to equal the X spacing. Again, you usually want to leave it that way.

   X measures horizontal distance; Y measures vertical distance. The AutoCAD drawing area normally shows an X and Y icon in case you forget.

   If you're an old AutoCAD hand and find the graph-paper grid too obtrusive, check the Display Dotted Grid In 2D Model Space box in the Grid Style area to switch to the old-style rows and columns of dots.

6. Specify additional grid display options in the Grid Behavior area.

   If you select the Adaptive Grid check box, AutoCAD changes the density or spacing of the grid lines or dots as you zoom in and out. If you also select Allow Subdivision Below Grid Spacing, the spacing can go lower than what you've set, and it may go higher if you're zoomed a long way out of your drawing. (If it didn't, you couldn't see your drawing for the grid!)

   Selecting the Display Grid Beyond Limits check box allows the grid to display over the entire drawing area, no matter how far you're zoomed out. Clearing this check box makes AutoCAD behave the way it's always behaved — that is, the grid is displayed only in the area defined by the drawing limits.

   The Follow Dynamic UCS option (not available in AutoCAD LT) is a 3D-specific feature that changes your drawing plane as you mouse over 3D objects. I cover this feature in Chapter 22.

7. Click OK to close the Drafting Settings dialog box.

Setting linetype and dimension scales

Even though you've engraved the drawing scale factor on your desk and written it on your hand — not vice versa — AutoCAD doesn't know the drawing scale until you enter it. Keeping AutoCAD in the dark is fine as long as you're just drawing continuous lines and curves representing real-world geometry because you draw these objects at their real-world size, without worrying about plot scale.

However … as soon as you start using non-continuous dash-dot linetypes (line patterns that contain gaps in them), you need to tell AutoCAD how to scale the gaps in the linetypes based on the plot scale. If you forget this, the dash-dot linetype patterns can look waaaay too big or too small. Figure 4-6 shows what I mean.

Figure 4-6: … and this little center line looks juuuust right!

The scale factor that controls dash-dot linetypes is found in a system variable called LTSCALE (as in LineType SCALE). You can change this setting at any time, but it's best to set it correctly when you're setting up the drawing.

The following sequence includes directions for typing system variable and command names. To set the linetype scale at the keyboard, follow these steps:

1. Type LTSCALE (or LTS) and press Enter.

   AutoCAD responds with a prompt, asking you for the scale factor. The value at the end of the prompt is the current linetype scale setting, as shown in the following command line example:

   Enter new linetype scale factor <1.0000>:

2. Type the value you want for the linetype scale and press Enter.

   The easiest choice is to set the linetype scale to the drawing scale factor. Some people, however, find that the dashes and gaps in dash-dot linetypes get a bit too long when they use the drawing scale factor. If you're one of those people, set LTSCALE to one-half of the drawing scale factor. (Feel free to experiment with this value; some people prefer a linetype scale of three-quarters the scale factor. If you're working in metric, try 0.75 times the scale factor instead — just ask your calculator if you don't believe me.)

   Alternatively, you can specify linetype scale in the Linetype Manager dialog box: Click the Linetype drop-down on the Properties panel of the Ribbon's Home tab and select Other. Then, in the Linetype Manager dialog box, click the Show Details button, and type your desired linetype scale in the Global Scale Factor text box.

• PSLTSCALE: Makes linetype spacing look the same in paper space viewports, regardless of the viewport scale.
• CELTSCALE: Changes the effective linetype scale factor for new objects.
• MSLTSCALE: Visually displays dash-dot linetypes in the model tab based on the annotative scale setting.

If any of these sound useful — and I highly recommend you enable PSLTSCALE — check them out in the online help index.

Entering drawing properties

I recommend one last bit of housekeeping before you're finished with model-space drawing setup: Enter summary information in the Drawing Properties dialog box, as shown in Figure 4-7. Click the Application button; in the Drawing Utilities section, choose Drawing Properties to open the Drawing Properties dialog box; then click the Summary tab. Enter the drawing scale and the drawing scale factor you're using in the Comments area, plus any other information you think useful.

Figure 4-7: Surveying your drawing's properties.