AutoCAD 2005 For Dummies (2004)

100 Part II: Let There Be Lines

Chapter 5

Where to Draw the Line

In This Chapter

Drawing with the AutoCAD drawing commands

Lining up for lines and polylines

Closing up with rectangles and polygons

Rounding the curves with circles, arcs, splines, and clouds

Dabbling in ellipses and donuts

Making your points

As you probably remember from your crayon and coloring book days, drawing stuff is fun. CAD imposes a little more discipline, but drawing

AutoCAD objects is still fun. In computer-aided drafting, you usually start by drawing geometry — shapes such as lines, circles, rectangles, and so on that represent the real-world object that you’re documenting. This chapter shows you how to draw geometry.

After you’ve created some geometry, you’ll probably need to add some dimensions, text, and hatching, but those elements come later (in Part III of this book). Your first task is to get the geometry right; then you can worry about labeling things.

Drawing geometry properly in AutoCAD depends on paying attention to object properties and the precision of the points that you specify to create the objects. I cover these matters in Chapter 4, so if you eagerly jumped to this chapter to get right to the fun stuff, take a moment to review that chapter first.

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Introducing the AutoCAD

Drawing Commands

For descriptive purposes, this chapter divides the drawing commands into three groups:

Straight lines and objects composed of straight lines

Curves

Points

AutoCAD-based application-specific programs such as Architectural Desktop add extra drawing tools to the mix — for example, commands for drawing walls and doors. See the documentation that comes with the applicationspecific program for information on such tools.

Table 5-1 offers an overview of most of the drawing commands in AutoCAD, without the 3D-related commands. It describes the commands’ major options and shows you how to access them from the command line, the Draw menu, and the Draw toolbar. (Don’t worry if not all the terms in the table are familiar to you; they become clear as you read through the chapter and use the commands.)

	Table 5-1			AutoCAD Drawing Commands
	Button		Command	Major Options	Toolbar Button	Draw Menu
			Line	Start, end points	Line	Line
			RAY	Start point, point	None	Ray
				through which ray
				passes
			XLine	Two points on line	Construction line	Construction line
			PLine	Vertices	Polyline	Polyline
			POLygon	Number of sides,	Polygon	Polygon
						inscribed/
						circumscribed

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	Button		Command	Major Options	Toolbar Button	Draw Menu
			RECtang	Two corners	Rectangle	Rectangle
			Arc	Various methods	Arc	Arc; submenu for
				of definition		definition methods
			Circle	Three points, two	Circle	Circle; submenu
				points, tangent		for definition
						methods
			REVCLOUD	Arc length	Revcloud	Revision Cloud
			DOnut	Inside, outside	None	Donut
				diameters
			SPLine	Convert polyline	Spline	Spline
				or create new
			ELlipse	Arc, center, axis	Ellipse	Ellipse; submenu
						for definition
						methods
			POint	Point style	Point	Point; submenu
						for definition
						methods

Many of the choices on the AutoCAD Draw menu open submenus containing several variations on each drawing command.

The AutoCAD drawing commands depend heavily on your reading the command line area and sometimes typing things there. Don’t worry; I remind you to do so. (If “command line area” sounds to you like a place to order cafeteria food, not an AutoCAD essential concept, see Chapter 2.) Many of the command options that you see in command line prompts are available as well by right-clicking in the drawing area.

So what’s the best course: to enter drawing commands from the command line or to choose them from the menus or toolbars? I suggest that you start a drawing command the first few times — until you remember its command name — by clicking its button on the Draw toolbar. After you click the button, fasten your eyes on the command line area so that you see the name of the command and its command line options. Use the keyboard or the right-click menus to

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select options, depending on whether your hand is on the keyboard or the mouse at that moment. After you’re acquainted with a drawing command and decide that you like it enough to use it often, find out how to type its keyboard shortcut (the uppercase letters in the command names in Table 5-1).

A few drawing commands, such as DOnut, aren’t on the Draw toolbar; you have to type those or choose them on the Draw menu.

The Straight and Narrow: Lines,

Polylines, and Polygons

As I harp on a bunch of times elsewhere in this book, CAD programs are for precision drawing, so you’ll spend a lot of your AutoCAD time drawing objects composed of straight-line segments. This section covers these commands:

Line: Draws a series of straight line segments; each segment is a separate object

PLine: Draws a polyline — a series of straight and/or curved line segments; all the segments remain connected to each other as a single object

RECtang: Draws a polyline in the shape of a rectangle

POLygon: Draws a polyline in the shape of a regular polygon (that is, a closed shape with all sides equal and all angles equal)

The following additional straight-line drawing commands also are available in AutoCAD:

RAY: Draws a semi-infinite line (a line that extends infinitely in one direction)

XLine: Draws an infinite line (a line that extends infinitely in both directions)

The RAY and XLine commands are used to draw construction lines that guide the construction of additional geometry. Drawing construction lines is less common in AutoCAD than in some other CAD programs. AutoCAD’s many precision techniques often provide more efficient methods than construction lines of creating new geometry.

Toe the line

The Line command in AutoCAD draws a series of one or more connected line segments. Well, it appears to draw a series of connected segments. In fact,

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each segment, or piece of a line with endpoints, is a separate object. This construction doesn’t seem like a big deal until you try to move or otherwise edit a series of segments that you drew with the Line command; you must select every piece separately. To avoid such a hassle, use polylines, described later in this chapter, not lines and arcs when you want the connected segments to be a single object.

If you’re used to drawing lines in other programs, you may find it confusing at first that AutoCAD’s Line command doesn’t stop after you draw a single segment. AutoCAD keeps prompting you to specify additional points so that you can draw a series of (apparently) connected segments. When you’re finished drawing segments, just press the Enter key to finish the Line command and return to the Command prompt.

Unlike a lot of AutoCAD drawing commands, Line doesn’t offer a bunch of potentially confusing options. There’s a Close option to create a closed polygon and an Undo option to remove the most recent segment that you drew.

Like all drawing commands, Line puts the line segment objects that it draws on the current layer, and uses the current color, linetype, lineweight, and plot style properties.

Make sure that you’ve set these properties correctly before you start drawing. (I recommend that you set color, linetype. lineweight, and plot style to ByLayer.) See Chapter 4 for information on setting the current properties with the Object Properties toolbar.

When you’re doing real drafting as opposed to just experimenting, make sure that you use one of AutoCAD’s precision tools, such as object snaps, typed coordinates, or tracking to ensure that you specify each object point precisely. Chapter 4 describes these tools.

Follow these steps to draw a series of line segments by using the Line command:

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

2.Click the Line button on the Draw toolbar.

AutoCAD starts the Line command and prompts you at the command line:

Specify first point:

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

Remember to use one of the precision techniques described in Chapter 4 if you’re doing real drafting. For the first point, object snap, snap, tracking, and typing coordinates all work well.

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AutoCAD prompts you at the command line to specify the other endpoint of the first line segment:

Specify next point or [Undo]:

4.Specify additional points by clicking or typing.

Again, use one of the AutoCAD precision techniques if you’re doing real drafting. For the second and subsequent points, all the techniques mentioned in the previous step work well, plus ortho and direct distance entry.

After you specify the third point, AutoCAD adds the Close option to the command line prompt:

Specify next point or [Close/Undo]:

5.When you’re finished drawing segments, end with one of these steps:

•Press Enter, or right-click anywhere in the drawing area and choose Enter (as shown in Figure 5-1), to leave the figure open.

•Type C and press Enter, or right-click anywhere in the drawing area and choose Close from the cursor menu, to close the figure.

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

Command:

Figure 5-1:

Line it up: Drawing line segments with the Line command.

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Connect the lines with polyline

The Line command is fine for some drawing tasks, but the PLine command is a better, more flexible choice in many situations. The PLine command draws a special kind of object called a polyline. You may hear CAD drafters refer to a polyline as a pline because of the command name. (By the way, PLine is pronounced to rhyme with “beeline” — in other words, it sounds like the place you stand when you’ve drunk a lot of beer at the ball game.)

The most important differences between the Line and PLine commands are these:

The Line command draws a series of single line segment objects. Even though they appear on the screen to be linked, each segment is a separate object. If you move one line segment, the other segments that you drew at the same time don’t move with it. The PLine command, on the other hand, draws a single, connected, multisegment object. If you select any segment for editing, your changes affect the entire polyline. Figure 5-2 shows how the same sketch drawn with the Line and the PLine commands responds when you select one of the objects.

Use the PLine command instead of Line in most cases where you need to draw a series of connected line segments. If you’re drawing a series of end- to-end segments, there’s a good chance that those segments are logically connected — for example, they might represent the outline of a single object or a continuous pathway. If the segments are connected logically, it makes sense to keep them connected in AutoCAD. The most obvious practical benefit of grouping segments together into a polyline is that many editing operations are more efficient when you use polylines. If you move a single, disconnected line segment, the other segments that you drew at the same time don’t move with it — likewise for other common editing operations, such as copying, erasing, rotating, and mirroring. When you select any segment in a polyline for editing, the entire polyline is affected.

The PLine command can draw curved segments as well as straight ones.

You can add width to each segment of a polyline. Polyline segment width is similar to lineweight, except that it can be uniform or tapered. The ability to create polyline segments with line widths was more important in the old days before AutoCAD had lineweight as an object property. People used to draw polylines with a small amount of width to show the segments as somewhat heavier than normal on plots. Nowadays, it’s easier and more efficient to achieve this effect with object lineweights (as described in Chapter 4) or plot styles (as described in Chapter 12).

After you create a polyline, you can adjust its segments by grip editing any of the vertex points. (The little squares on the vertices in Figure 5-2 are called grips; see Chapter 6 for details on grip editing.) For more complicated polyline editing tasks, you can use the PEdit command to edit the polyline, or you can convert the polyline to a collection of line and arc segments by using the

108 Part II: Let There Be Lines

eXplode command — although you lose any width defined for each segment when you explode a polyline.

Drawing polylines composed of straight segments is pretty much like drawing with the Line command, as demonstrated in the following procedure. Watch the command prompts carefully because the PLine command has a lot of options! Remember that you can right-click in the drawing area to select one of the options, but reading the command prompts is your ticket to knowing what the options are at any moment.

Polyline (all segments form one object)

Figure 5-2:

Results of drawing with the Line and PLine commands.

Line (each segment is a separate object)

To draw a polyline composed of straight segments, follow these steps:

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

2.Click the Polyline button — the one that looks like a fishhook — on the Draw toolbar.

AutoCAD starts the PLine command and prompts you at the command line:

Specify start point:

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

AutoCAD displays the current polyline segment line-width and prompts you to specify the other endpoint of the first polyline segment:

Current line-width is 0.0000

Specify next point or [Arc/Halfwidth/Length/Undo/Width]:

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4.If the current line-width isn’t zero, change it to zero by typing W, Enter, 0, Enter, 0 (as shown in the following command line sequence).

Specify next point or [Arc/Halfwidth/Length/Undo/Width]:

W

Enter Specify starting width <0.0000>: 0

Enter Specify ending width <0.0000>: 0 Enter Specify next point or

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

Despite what you may think, a zero width polyline segment is not the AutoCAD equivalent of writing with disappearing ink. “Zero width” means “display this segment, using the normal, thin line-width on the screen.” AutoCAD still applies object property or plot style lineweights when you plot.

5. Specify additional points by clicking or typing.

After you specify the second point, AutoCAD adds the Close option to the command line prompt:

Specify next point or

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

In addition, you can view and choose options from the right-click menu, as shown in Figure 5-3.

Figure 5-3:

Getting in

the PLine.