AutoCAD 2005 For Dummies (2004)

110 Part II: Let There Be Lines

6.After you finish drawing segments, either press Enter (to leave the figure open) or type C and press Enter (to close it).

AutoCAD draws the final segment and returns to the Command prompt, indicating that the PLine command is finished:

Command:

In the following procedure, I spice things up a bit and give you a preview of coming (curvy) attractions by adding an arc segment to a polyline.

Just so you know, curved segments in polylines are circular arcs — pieces of circles that you can draw with the AutoCAD Arc command. AutoCAD can draw other kinds of curves, including ellipses and splines, but not within the PLine command.

To draw a polyline that includes curved segments, follow these steps:

1.Repeat Steps 1 through 5 of the previous procedure.

2.When you’re ready to add one or more arc segments, type A and press Enter to select the Arc option.

The command line prompt changes to show arc segment options. Most of these options correspond to the many ways of drawing circular arcs in AutoCAD; see “Arc-y-ology,” later in this chapter.

Specify endpoint of arc or [Angle/CEnter/CLose/Direction/Halfwidth/Line/ Radius/Second pt/Undo/Width]:

3. Specify the endpoint of the arc by clicking a point or typing coordinates.

AutoCAD draws the curved segment of the polyline. The command line prompt continues to show arc segment options.

Specify endpoint of arc or [Angle/CEnter/CLose/Direction/Halfwidth/Line/ Radius/Second pt/Undo/Width]:

Your options at this point include

•Specifying additional points to draw more arc segments

•Choosing another arc-drawing method (such as CEnter or

Second pt)

•Returning to drawing straight-line segments with the Line option In this example, I return to drawing straight-line segments.

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Perhaps the most useful of the alternative arc-drawing methods is Second pt. You can use it to gain flexibility in the direction of the arc, but at the cost of losing tangency of contiguous segments. Sometimes it’s best not to go off on a tangent, anyway.

4. Type L and press Enter to select the Line option.

Specify endpoint of arc or [Angle/CEnter/CLose/Direction/Halfwidth/Line/ Radius/Second pt/Undo/Width]: L

The command line prompt changes back to showing straight-line segment options.

Specify next point or

[Arc/Close/Halfwidth/Length/Undo/Width]:

5.Specify additional points by clicking or typing.

6.After you’re finished drawing segments, either press Enter or type C and press Enter.

Command:

Figure 5-4 shows some of the things that you can draw with the PLine command by using straight segments, arc segments, or a combination of both.

Figure 5-4:

A plethora of polylines.

The Line and PLine commands work well for drawing a series of end-to-end single lines, but what if you want to draw a series of double lines to represent, for example, the edges of a wall or roadway? Here are three options:

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Use the AutoCAD MLine command to draw multilines — series of two or more parallel, straight lines. The AutoCAD multiline feature was full of limitations and bugs when it debuted ten years ago. It hasn’t improved significantly since then. Look up the MLine and MLSTYLE commands in AutoCAD’s online help system if you’d like to tangle with this feature, but be prepared to spend time experimenting and struggling.

In AutoCAD LT only, use the DLine (Double Line) command to draw pairs of parallel line and/or arc segments. AutoCAD LT doesn’t include the MLine command, which, given MLine’s problems, probably is more of a blessing than a limitation. AutoCAD, on the other hand, doesn’t include the DLine command. (Score one for the little brother!)

Use the PLine command to draw a single set of connected line and/or arc segments, and then use the Offset command to create one or more sets of parallel segments. Chapter 6 covers the Offset command.

Square off with rectangle

You can use the PLine or Line command to draw a rectangle segment by segment. In most cases, though, you’ll find it easier to use the special-purpose RECtang command. The following procedure demonstrates how:

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

2.Click the Rectangle button on the Draw toolbar.

AutoCAD starts the RECtang command and prompts you at the command line to specify a point for one corner of the rectangle:

Specify first corner point or

[Chamfer/Elevation/Fillet/Thickness/Width]:

You can add fancy effects with the additional command options. The default options work best for most purposes. Look up “RECTANG command” in the AutoCAD help system if you want to know more about the options.

3. Specify the first corner by clicking a point or typing coordinates.

The command line prompts you to specify the other corner of the rectangle — the one that’s diagonally opposite from the first corner:

Specify other corner point or [Dimensions]:

4. Specify the other corner by clicking a point or typing coordinates.

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If you know the size of the rectangle that you want to draw (for example, 100 units long by 75 units high), type relative coordinates to specify the dimensions (for example, @100,75). (Chapter 4 describes how to type coordinates.)

AutoCAD draws the rectangle.

Choose your sides with polygon

Rectangles and other closed polylines are types of polygons, or closed figures with three or more sides. The AutoCAD POLygon command provides a quick way of drawing regular polygons — polygons in which all sides and angles are equal. (If regular polygons seem a little square, maybe that’s because a square is a special case of a regular polygon!)

The following procedure demonstrates the POLygon command:

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

2.Click the Polygon button on the Draw toolbar.

AutoCAD starts the POLygon command and prompts you at the command line to enter the number of sides for the polygon:

Enter number of sides <4>:

3.Type the number of sides in the polygon that you want to draw and press Enter.

The command line prompts you to specify the center point of the polygon:

Specify center of polygon or [Edge]:

You can use the Edge option to draw a polygon by specifying one side, instead of the center and radius of an imaginary inscribed or circumscribed circle. The imaginary circle method is much more common.

4.Specify the center point by clicking a point or typing coordinates.

The command line prompts you to specify whether the polygon will be inscribed in or circumscribed about an imaginary circle whose radius you will specify in the following step:

Enter an option [Inscribed in circle/Circumscribed about

circle] <I>:

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5.Type I or C and press Enter.

The command line prompts you to specify the radius of imaginary circle:

Specify radius of circle:

6.Specify the radius by typing a distance or clicking a point.

AutoCAD draws the polygon.

If you type a distance or you click a point with Ortho turned on, the polygon will be aligned orthogonally, as shown in Figure 5-5. If you click a point with Ortho turned off, the polygon most likely won’t be aligned orthogonally.

Figure 5-5 shows the results of drawing plenty of polygons — a practice known as “polygony,” and which, as far as I know, remains legal in most states.

Rectangles and polygons in AutoCAD are really just polylines that you specify in a way that’s appropriate to the shape you’re creating. You’ll notice this when you grip edit a rectangle or polygon and move one of the vertexes: Only the selected vertex moves. AutoCAD doesn’t make the entire rectangle or polygon larger or smaller. (See Chapter 6 for information about grip editing.)

Figure 5-5:

A polygonal party.

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(Throwing) Curves

Although straight line segments predominate in many CAD drawings, even the most humdrum, rectilinear design is likely to have a few curves. And if you’re drawing car bodies or Gaudí buildings, your drawings will be almost nothing but curves! This section shows you how to use the following AutoCAD curve-drawing commands:

Circle: Draws circles (you were expecting rectangles, maybe?)

Arc: Draws circular arcs — arcs cut from circles, not from ellipses, parabolas, or some other complicated curve

ELlipse: Draws ellipses and elliptical arcs

SPLine: Draws smoothly flowing curves of a variety of shapes

DOnut: Draws filled-in annular rings and circles

REVCLOUD: Draws free-form “clouds,” the most common application of which is to indicate revised areas in the drawing

The following sections describe each command.

Going full circle

AutoCAD offers an easy way to draw circles, and it also offers . . . other ways. The easy way is to define the center point of the circle and then to define the radius or diameter. You can also define a circle by entering one of the following options of the command (for those “other” ways):

3P (3-Point): Specify any three points on the circumference.

2P (2-Point): Specify the endpoints of a diameter of the circle.

Ttr (Tangent-Tangent-Radius): Specify two lines or other objects that are tangent to the circle, and then specify its radius.

Whether these additional circle-drawing methods are useful or superfluous depends on the kinds of drawings that you make and how geometry is defined in your industry. Get familiar with the default center point/radius method and then try the other methods to see whether they may be helpful to you. If you find yourself going around in circles, you can always draw them the default way and move them into position with other geometry.

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

2.Click the Circle button on the Draw toolbar.

AutoCAD starts the Circle command and prompts you at the command line to specify the center point of the circle:

Specify center point for circle or [3P/2P/Ttr (tan tan

radius)]:

The prompt shows the methods other than “center point plus radius” that you can use to draw circles in AutoCAD. (No, “tan tan radius” is not a mathematician’s dance.) Look up “CIRCLE command” in the online help if you think you may have a use for these less common circledrawing methods.

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

Use one of the precision techniques described in Chapter 4 if you’re doing real drafting. Object snap, snap, and typing coordinates all work well for specifying the center point.

The command line then prompts you to specify the circle’s radius:

Specify radius of circle or [Diameter]:

Type D and press Enter if you prefer to enter the diameter rather than the radius and you’ve forgotten your twos tables — or, more seriously, if the diameter is easier to specify with the cursor or type exactly than the radius is.

4.Specify the radius by typing a distance or clicking a point.

AutoCAD draws the circle, as shown in Figure 5-6.

Arc-y-ology

Arcs in AutoCAD are, quite simply, pieces of circles. As with circles, AutoCAD offers you an easy way to define arcs. Just specify three points on-screen to define the arc, easy as one-two-three. These points tell AutoCAD where to start the arc, how much to curve it, and where to end it.

Sounds pretty easy, right? So where’s the problem? The trouble is that you often must specify arcs more exactly than is possible by using this method. AutoCAD helps you specify such arcs, too, but the procedure ain’t easy.

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Figure 5-6:

Pi R square(d); circles are round.

You can start your arc by specifying the center of the arc or the start point. If you choose the Center option, AutoCAD prompts you for the center point first and the start point second. AutoCAD defines arcs counterclockwise, so pick a start point in a clockwise direction from the end point. After you specify the center and start point, AutoCAD presents several options you can choose, including the following:

Angle: This option specifies the included angle that the arc sweeps out. A 180-degree angle, for example, is a semicircle.

Length of chord: This option specifies the length of an imaginary straight line connecting the endpoints of the arc. Most people use this option seldom or never.

Endpoint: This option specifies where the arc ends. It’s the default option and is often the easiest to use.

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If you specify the start point as the first option, you can choose among the following three command line options as well:

Center: This option prompts you for the arc’s center point and then finishes with the three options listed above.

End: This option specifies the endpoint of the arc. You then need to define the angle the arc covers, its direction, its radius, or its center point.

Second point: This is the default option. The second point you choose is not the endpoint; instead, it’s a point on the arc that, along with the start and endpoints, defines the arc’s curvature — that is, how much it curves. After you enter the second point, you must enter an endpoint to complete the arc.

To get a feel for how these permutations can be strung together to create different arc-drawing methods, choose Draw Arc and look at the impressive submenu that unfurls, as shown in Figure 5-7.

Figure 5-7:

A deluge of Arc options, with the results of using some of those options.

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The following example shows how you draw an arc with the default start point/second point/endpoint method:

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

2.Click the Arc button on the Draw toolbar.

AutoCAD starts the Arc command and prompts you at the command line to specify the first endpoint of the arc:

Specify start point of arc or [Center]:

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

The command line prompts you to specify a second point on the arc:

Specify second point of arc or [Center/ENd]:

4.Specify a second point on the arc by clicking a point or typing coordinates.

The second point lies somewhere along the curve of the arc. AutoCAD determines the exact curvature of the arc after you choose the final endpoint in the following step. To align the second point with an existing object, use an object snap mode.

The command line prompts you to specify the other endpoint of the arc; as you move the cursor around, AutoCAD shows how the arc will look:

Specify end point of arc:

5.Specify the other endpoint of the arc by clicking a point or typing coordinates.

AutoCAD draws the arc, as shown in Figure 5-7.

Ellipses (S. Grant?)

An ellipse is like a warped circle with a major (long) axis and a minor (short) axis. These axes determine the ellipse’s length, width, and degree of curvature. An elliptical arc is an arc cut from an ellipse. Some kinds of drawing geometry require ellipses or elliptical arcs, but many people use AutoCAD happily for years without ever drawing an ellipse. If you think you’re one of those people, skip this section.

The AutoCAD ELlipse command provides a straightforward way of drawing an ellipse: You specify the two endpoints of one of its axes and then specify an endpoint on the other axis. But like the Arc command, the ELlipse command offers a bunch of other options on the command line: