AutoCAD 2005 For Dummies (2004)

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Arc: This option generates an elliptical arc, not a full ellipse. You define an elliptical arc just as you do a full ellipse. The following methods for creating an ellipse apply to either.

Center: This option requires that you define the center of the ellipse and then the endpoint of an axis. You can then either enter the distance of the other axis or specify that a rotation around the major axis define the ellipse. If you choose the latter, you can enter (or drag the ellipse to) a specific rotation for the second axis that, in turn, completely defines the ellipse.

Rotation: With this option, you specify an angle, which defines the curvature of the ellipse — small angles make fat ellipses (0 degrees creates a circle, in fact), and large angles make skinny ellipses. The name of the option, Rotation, has something to do with rotating an imaginary circle around the first axis. If you can figure out the imaginary circle business, then you have a better imagination than I do.

The following example creates an ellipse by using the default endpoints of the axes method. Figure 5-8 shows an ellipse and an elliptical arc.

Figure 5-8:

An ellipse and elliptical arc.

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Command: ELlipse Enter

Specify axis endpoint of ellipse or [Arc/Center]: pick or type the first endpoint of one axis

Specify other endpoint of axis: pick or type the other endpoint of one axis

Specify distance to other axis or [Rotation]: pick or type the endpoint of the other axis

You can create elliptical arcs (as opposed to the circular arcs that the AutoCAD Arc command draws) by using the Arc option of the ELlipse command; it’s perfect for drawing those cannonball trajectories! Alternatively, you can draw a full ellipse and use the TRIM or BREAK command to cut a piece out of it.

Splines: The sketchy, sinuous curves

Most people use CAD programs for precision drawing tasks: straight lines, carefully defined curves, precisely specified points, and so on. AutoCAD is not the program to free your inner artist — unless your inner artist is Mondrian. Nonetheless, even meticulously created CAD drawings sometimes need free-form curves. The AutoCAD spline object is just the thing for the job.

Although PLine is pronounced to rhyme with “beeline,” SPLine rhymes with “vine.” (If you liked my earlier pronunciation comment, you may want to think about beer before you say “PLine” and about wine before you say “SPLine.”)

You can use AutoCAD splines in two ways:

Eyeball the location and shape of the curve and don’t worry too much about getting it just so. That’s the free-form, sketchy, not-too-precise approach that I describe here.

Specify their control points and curvature characteristics precisely. Beneath their easy-going, informal exterior, AutoCAD splines are really highly precise, mathematically defined entities called NURBS curves (Non-Uniform Rational B-Spline curves). Mathematicians and some mechanical and industrial designers care a lot about the precise characteristics of the curves they work with. For those people, the AutoCAD SPLine and SPlinEdit commands include a number of advanced options. Look up “spline curves” in the AutoCAD online help if you need precision in your splines.

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Drawing splines is straightforward, if you ignore the advanced options. The following procedure draws a free-form curve with the SPLine command:

1.Set object properties to the layer and other properties that you want applied to the spline that you’ll draw.

2.Click the Spline button on the Draw toolbar.

AutoCAD starts the SPLine command and prompts you at the command line to specify the first endpoint of the spline:

Specify first point or [Object]:

3.Specify the start point by clicking a point or typing coordinates.

The command line prompts you to specify additional points:

Specify next point:

4.Specify additional points by clicking or typing coordinates.

After you pick the second point, the command line prompt changes to show additional options:

Specify next point or [Close/Fit tolerance] <start tangent>:

Because you’re drawing a free-form curve, you usually don’t need to use object snaps or other precision techniques when picking spline points.

5. Press Enter after you’ve chosen the final endpoint of your spline.

AutoCAD prompts you to specify tangent lines for each end of the spline:

Specify start tangent:

Specify end tangent:

The Specify start tangent and Specify end tangent prompts can control the curvature of the start and end points of the spline. In most cases, just pressing Enter at both prompts to accept the default tangents works fine.

6.Press Enter twice to accept the default tangent directions.

AutoCAD draws the spline.

Figure 5-9 shows some examples of splines.

After you’ve drawn a spline, you can grip edit it to adjust its shape. See Chapter 6 for information about grip editing. If you need finer control over spline editing, look up the SPlinEdit command in the AutoCAD online help.

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Figure 5-9:

A slew of splines.

Donuts: The circles with a difference

Creating a donut is a simple way to define a single object that consists of two concentric circles with the space between them filled.

When you start the DOnut command, AutoCAD prompts you for the inside diameter and the outside diameter — the size of the hole and the size of the donut, as measured across their widest points. After you’ve entered these values, AutoCAD prompts you for the center point of the donut. But one donut is rarely enough, so AutoCAD keeps prompting you for additional center points until you press Enter (the AutoCAD equivalent of saying, “no, really, I’m full now!”).

The following example draws a regulation-size donut, with a 1.5-inch hole and 3.5-inch outside diameter. Figure 5-10 shows several kinds of donuts.

Command: DOnut Enter

Specify inside diameter of donut <0.5000>: 1.5 Enter Specify outside diameter of donut <1.0000>: 3.5 Enter Specify center of donut or <exit>: pick or type the center

point of one or more donuts

Specify center of donut or <exit>: Enter

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Figure 5-10:

Donuts, plain and jelly-filled.

You can use the DOnut command to create a filled circle — also known as a jelly-filled donut. Just specify an inside diameter of 0.

Revision clouds on the horizon

It’s customary in many industries to submit a set of drawings at a stage of completion and then submit them again later with revisions — corrections, clarifications, and requested changes. Often, the recipients like to locate changed stuff easily. A common drafting convention in many industries is to call attention to revised items by drawing free-form clouds around them. The REVCLOUD command makes quick work of drawing such clouds.

Drawing revision clouds is easy, after you understand that you click with the mouse only once in the drawing area. That one click defines the starting point for the cloud’s perimeter. After that, you simply move the cursor around, and the cloud takes shape. When you return to near the point that you clicked in the beginning, AutoCAD automatically closes the cloud.

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The following example shows you how to draw a revision cloud. Figure 5-11 shows what revision clouds look like.

Command: REVCLOUD

Minimum arc length: 0.5000 Maximum arc length: 0.5000

Style: Normal

Specify start point or [Arc length/Object/Style] <Object>:

pick a point along the perimeter of your future cloud

Guide crosshairs along cloud path... sweep the cursor around to define the cloud’s perimeter

You don’t need to click again. Simply move the cursor around without clicking. AutoCAD draws the next lobe of the cloud when your cursor reaches the Minimum arc length distance from the end of the previous lobe.

Continue moving the cursor around until you return to the point that you clicked at first.

Revision cloud finished.

Figure 5-11:

Cloud cover.

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Here are a few tips for using revision clouds:

It’s a good idea to put revision clouds on their own layer so that you can choose to plot with or without the clouds visible.

You’ll probably find it easier to control the shape of revision clouds if you turn off ortho mode before you start the command.

You may need to add a triangle and number, as shown in Figure 5-11, to indicate the revision number. A block with an attribute is a good way to handle this requirement: Chapter 13 covers blocks and attributes.

If the revision cloud’s lobes are too small or too large, erase the cloud, restart the REVCLOUD command, and use the command’s Arc length option to change the minimum and maximum arc lengths. The default minimum and maximum lengths are 0.5 (or 15 in metric drawings) multiplied by the DIMSCALE (DIMension SCALE) system variable setting. If you make the minimum and maximum lengths equal (which is the default), the lobes will be approximately equal in size. If you make them unequal, there will be more variation in lobe size — you’ll get “fluffier” clouds. Fortunately, of these options are more than most nonmeteorologists will need. If you’ve set DIMSCALE properly during your drawing setup procedure (see Chapter 3), REVCLOUD should do a pretty good job of guessing reasonable default arc lengths.

Scoring Points

I thought about not covering points in this book, but I didn’t want you complaining that AutoCAD 2005 For Dummies is pointless.

The word point describes two different things in AutoCAD:

A location in the drawing that you specify (by typing coordinates or clicking with the mouse)

An object that you draw with the POint command

Throughout this chapter and most of the book, I tell you to specify points — that’s the location meaning. This section tells you how to draw point objects.

A point object in AutoCAD can serve two purposes.

Points often identify specific locations in your drawing to other people who look at the drawing. A point can be something that displays on the screen, either as a tiny dot or as another symbol, such as a cross with a circle around it.

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You can use points as precise object snap locations. Think of them as construction points. For example, when you’re laying out a new building, you might draw point objects at some of the engineering survey points and then snap to those points as you sketch the building’s shape with the polyline command. You use the NODe object snap mode to snap to AutoCAD point objects. In this guise, points usually are for your use in drawing and editing precisely. Other people who view the drawing probably won’t even be aware that the point objects are there.

What makes AutoCAD point objects complicated is their almost limitless range of display options, provided to accommodate the two different kinds of purposes just described (and possibly some others that I haven’t figured out yet). You use the Point Style dialog box, shown in Figure 5-12, to specify how points should look in the current drawing.

DDPTYPE is the command that opens the Point Style dialog box. You can access it from the menus by choosing Format Point Style. The top portion of the dialog box shows the available point display styles. Most of the choices do pretty much the same thing. Just click one of the squares that says “hey, that’s a point!” to you.

Figure 5-12:

The Point Style dialog box controls the way point objects appear on-screen.

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The first choice, a single-pixel dot, is hard to see on the screen, and the second choice, invisible (a stealth point?), is impossible to see. Avoid these choices if you want your point objects to show up on the screen and on plots. The single-pixel dot, which is the default display style, works well if you use point objects as object snap locations and don’t want the points obtrusive on plots.

The remaining settings in the Point Style dialog box control the size at which points appear on the screen at different zoom resolutions. The default settings often work fine, but if you’re not satisfied with them, click the Help button to find out how to change them.

After you specify the point style, placing points on-screen is easy; the following example shows you how.

This is an example of the command-line commands to create a point:

Command: POint Enter

Current point modes: PDMODE=0 PDSIZE=0.0000

Specify a point: pick or type the coordinates of a location in the drawing

PDMODE and PDSIZE in the command prompt are system variables that correspond to the point display mode and display size options in the Point Style dialog box. If you want to know exactly how the system variables correspond to the dialog box choices, you have all the makings of a successful CAD nerd. Click the Help button in the Point Style dialog box to find out more (about the system variables — not about yourself).

If you start the POint command from the Draw toolbar or the Draw Point Multiple Point menu, it will repeat automatically — that is, it will prompt you repeatedly to Specify a point. When you’re finished drawing points, press Esc to finish the command for good. If the command doesn’t repeat automatically and you want to draw more points, press the Enter key to repeat the POint command and pick another location on the screen. Repeat as required: Enter, pick, Enter, pick, Enter pick . . . by now you should’ve gotten the point.

Chapter 6

Edit for Credit

In This Chapter

Using command-first editing

Selecting objects with maximum flexibility

Moving, copying, and stretching objects

Manipulating whole objects

Changing pieces of objects

Editing with grips

Editing object properties

Editing objects is the flip side of creating them, and in AutoCAD, you spend a lot of time editing — far more than drawing objects from scratch. That’s

partly because the design and drafting process is by its nature iterative, and also because CAD programs make it easy to edit objects cleanly.

When you edit objects in AutoCAD, you need to be just as concerned about specifying precise locations and distances as you are when you originally create the objects. Make sure that you’re familiar with the precision techniques described in Chapter 4 before you apply the editing techniques from this chapter to real drawings.

Commanding and Selecting

AutoCAD offers two main styles of editing:

Command-first editing

Selection-first editing

Within the selection-first editing style, you have an additional choice of editing that uses actual, named commands and direct manipulation of objects without named commands. The following sections cover these editing styles.