IN THIS CHAPTER

Drawing linear things with the AutoCAD drawing commands

Lining up for lines and polylines

Closing up with rectangles and polygons

As you may recall from your crayon-and-coloring-book days, drawing is fun. Computer-aided drafting (CAD) imposes a little more discipline, but drawing with AutoCAD is still fun. Trust me on this one. In computer-aided drafting, you usually start by drawing geometry from basic shapes — lines, circles, and rectangles — to represent the real-world object that you’re documenting.

For descriptive purposes, I divide the drawing commands into three groups:

• Straight lines and objects composed of straight lines, covered in this chapter
• Curves, which I explain in Chapter 7
• Points, explained in Chapter 7 as well if you’re wondering what the point of all this is

After you’ve created some straight or curvy geometry, you’ll probably need to add dimensions, text, and hatching, but those elements come later (in Part 3). Or you may want to use that geometry as the basis for some cool 3D modeling. I introduce you to that topic in Part 5. Your first task is to get the geometry right; then you can worry about labeling elements.

Drawing geometry properly in AutoCAD depends on the precision of the points that you specify to create the objects. I cover this topic in Chapter 8, so don’t start any production CAD drawings until you review that chapter.

Proper geometry creation also depends on creating objects that have the correct appearance. In Chapter 9, I show you how to create hidden lines, center lines, section lines, and other elements.

Drawing for Success

AutoCAD offers a wide range of tools that allow you to create designs in a virtual world that will be accurately manufactured or built in the real world. The 2D and 3D tools that you use require some upfront preparation to ensure that the designs you create are precisely drawn. Nothing is worse than spending time creating a great design, only to find out that the objects you drew weren’t drawn at the correct size and that lines don’t intersect. Okay, I lied. Worse yet is that your imprecise drawing was used to program a CNC machining center and now the expensive metal parts don’t fit.

Here are a few important techniques to use when you draw objects:

• Use precision tools to make sure objects intersect and are drawn at the correct angle. Precision tools allow you to reference points on existing objects, constrain the cursor to a specific angle or snap distance, and quickly locate a point based on a distance and direction in which the cursor is moved. I cover precision techniques and tools in Chapter 8.

• Understand the difference between command line and Dynamic Input coordinate entry. Second and next points entered at the command line are interpreted differently from those entered at the Dynamic Input tooltip. The second and next points entered at the Dynamic Input tooltip are formatted as polar and relative to the previously entered coordinate value automatically, unlike at the command line where you must first type @ before the coordinate value.

  AutoCAD’s Dynamic Input system displays a lot of the information at the cursor that you used to have to look down to the command line to see. To use Dynamic Input, make sure that the Dynamic Input button on the status bar is turned on (that is, it looks highlighted). You can also press F12 to toggle Dynamic Input on and off.

• Watch the command line. The command line at times displays additional information about the current command that’s not displayed in the Dynamic Input tooltip. This information might be the current text style or justification, or the active extend mode. I cover using the command line in Chapter 2.
• Organize objects on layers. All the objects you draw should be placed on specific layers. For example, annotation objects that communicate design information might be placed on a Notes layer, and the lines that are used to represent a wall might be placed on a Walls layer. I cover layers in Chapter 9.

Introducing the Straight-Line Drawing Commands

As I harp on elsewhere in this book, CAD programs are designed for precision drawing, so you’ll spend a lot of time in AutoCAD drawing objects composed of straight-line segments. The rest of this chapter covers these commands, all of which are found on the Draw panel of the Home tab on the Ribbon. The icons in the left margin match those from the Ribbon:

• Line: Draws a series of one or more visually connected straight-line segments; that is, the end of the current segment has the same coordinates as the start of the next segment. Although the lines appear to be physically connected, each segment (piece of a line with endpoints) is in fact a separate object with its own start and endpoints.
• PLine: Draws a polyline, which is a series of straight- or curved-line segments (or both) connected as a single object. I’m cheating slightly here because I cover curvy components in Chapter 7, but I don’t want you to have to read about one command in two different places.
• RECtang: Provides a convenient way to draw four equi-angular polyline segments. AutoCAD has no rectangle object.
• POLygon: Gives you a convenient way to draw a polyline in the shape of a regular polygon (a closed shape with all sides and all angles equal).

The POLygon command may be hidden under the Rectangle button on the Ribbon or vice versa, depending on which button you used last.

The following additional straight-line drawing commands, also available in AutoCAD LT, are found in the drop-down list below the Draw panel:

• XLine: Draws a line (known as an ex-line or a construction line) that passes through a point at a specified angle and extends to infinity in both directions.
• RAY: Draws a line (known as a ray) that starts at a point and extends to infinity at a specified angle away from the start point.

Use the RAY and XLine commands to draw construction lines that guide the construction of additional geometry. Drawing construction lines is less common in AutoCAD than in certain other CAD programs and is far less common than in pencil-and-paper drawings. The many precision techniques in AutoCAD usually provide methods for creating new geometry that are more efficient than adding construction lines to a drawing. In particular, object snap tracking (discussed in Chapter 8) and parametrics (discussed in Chapter 19) usually eliminate the need for construction geometry or even for a mitre line when creating orthographic views.

Although xlines and rays are infinitely long, they don’t increase the extents of your drawing to infinity. The question of the day is, “Which is longer; an XLine that extends to infinity in both directions or a RAY that extends to infinity in one direction?”

Drawing Lines and Polylines

The Line command works well for many drawing tasks, but the PLine command works better for others. Experience can help you choose which will work best for design needs. The PLine command draws a special kind of object — a polyline — and you might hear CAD drafters refer to a polyline as a p-line (rhymes with “bee-line,” not to be confused with the queue in a busy restroom).

Here are the primary differences between the Line and PLine commands:

• The Line command draws a series of separate line segments. Even though they appear to be connected onscreen, each one is a separate object. If you move one line segment, none of the other segments you drew at the same time moves with it.

• The PLine command draws a single, connected, multisegment object. A polyline is what a line appears to be; each segment is connected to form a single object. If you select any segment for editing, the changes affect the entire polyline. Figure 6-1 shows how the same sketch drawn with the Line and the PLine commands responds when you select one of the objects. A polyline is not a pickup line used by parrots in a bar.

  Use the PLine command rather than the Line command 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, those segments may well be 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 into a polyline is that many editing operations are more efficient when you use polylines. When you select any segment in a polyline for editing, the entire polyline is selected.

  As covered in Chapter 19, using parametrics on line segments can often produce the same results as using the PLine command.

• The PLine command can draw curved segments as well as straight ones. If you want a combination of separate linear and curved segments, you must switch between the Line and Arc commands. (I cover arcs in Chapter 7.) Using the PLine command, though, you can switch between linear or circular-curve segments within a single polyline.
• A polyline can have width. Polyline segment width is visually similar to the lineweight object property in AutoCAD (which I discuss in Chapter 9) except that polyline width can vary from segment to segment, and individual segments can be tapered. Polylines are often used for the copper conductors on electronic printed circuit boards.
• Polylines can be smooth. After drawing a polyline, you can use the PEdit command to automatically reshape the polyline into a smooth, flowing curve based on the vertex points you selected. I touch on this topic in Chapter 11.

The following sections show you how to create a line and a polyline.

Connecting the lines with polyline

Drawing polylines composed of straight segments is much like drawing with the Line command, as shown in the steps in this section. The PLine command has lots of options, so watch the prompts. If the Dynamic Input feature is on, press the down-arrow key to see the options listed near the cursor, or right-click to display the PLine right-click menu, or simply read the command line.

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

1. Click the Polyline button on the Draw panel of the Ribbon, or type PL at the command line and press Enter.

   AutoCAD starts the PLine command and prompts you to specify a start point.

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

   Now you truly need to read the command line because the Dynamic Input tooltip at the cursor doesn’t display any of the options.

   You can right-click or press the down-arrow key to see a list of the options at the cursor, as shown in Figure 6-2, but it’s usually faster to use the command line.

   AutoCAD displays the current polyline segment line width at the command line 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]:

3. If the current line width isn’t zero, change it to zero by typing W to select the Width option and then entering 0 as the starting and ending widths, as shown in this command-line sequence:

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

   Specify starting width <0.0000>: 0

   Specify ending width <0.0000>: 0

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

   Despite what you may think, a zero-width polyline segment isn’t the AutoCAD equivalent of drawing with invisible ink. Zero width means, “Display this segment using the normal, single-pixel width on the screen, and plot as thin as possible.” How can you tell when your pen has run out of invisible ink? You can see the writing.

4. Specify additional points by clicking or typing.

   After you specify the second point, AutoCAD adds the Close option to the prompt. The command line shows

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

   What you do next can get a little weird. If you invoke the Close option after selecting only the first and second points, PLine doubles back on itself and creates the second segment back over the first. Normal practice would be to not invoke Close until you have created at least two non-collinear segments.

5. Pick several points to create several line segments, and then enter W to start the Width option. Then set a new width, as shown in this command line sequence:

   Starting width <0.0000>: 5

   Specify ending width <5.0000>: Press Enter

6. Pick several more points and note the line width of the new segments.
7. Set the Width option again:

   Starting width <5.0000>: 15

   Specify ending width <0.0000>: 0

8. Pick another point.

   You just created a cool arrowhead!

   Any time AutoCAD prompts for a length or distance, you can either type a value or you can show it what you want by picking two points.

9. After you finish drawing segments, press Enter to leave the figure open or type C and press Enter to close it back to the start.

   AutoCAD draws the final segment and miters all the corners perfectly.

After you create a polyline, you can adjust its segments by grip-editing any of the vertex points. See Chapter 11 for details on grip editing.

In the following steps, I spice things up by adding an arc segment to a polyline.

Curved segments within polylines are circular arcs that you can create while running the PLine 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 1–4 in the preceding step list.

2. To add one or more arc segments, type A and then press Enter to select the Arc option.

   The prompt changes to show arc segment options. Most of these options correspond to the many ways of drawing circular arcs in AutoCAD; see the section on arcs in Chapter 7. The command line shows:

   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 prompts continue to show arc segment options.

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

   The options at this point are to

   • Specify additional points to draw more arc segments.
   • Choose another arc-drawing method, such as CEnter or Second point.
   • Return to drawing straight-line segments with the Line option.

   In this example, you draw straight-line segments.

   Perhaps the most useful of the alternative arc-drawing methods is Second pt. It gives you more control over the direction of the arc but at the cost of losing tangency of adjacent segments. (Sometimes, it’s best not to go off on a tangent, anyway.) If you want both ends of the arc segments to be tangent to the adjacent line segments, you should generally draw the polyline as straight-line segments and then use the Fillet command (described in Chapter 11) to add the arcs later.

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

   The prompt reverts 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.

Figure 6-3 shows some elements you can draw with the PLine command by using straight segments, arc segments, varying-width segments, or a combination of all of them.

Squaring Off with Rectangles

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

1. Click the Rectangle button on the Draw panel of the Home tab, or type REC and press Enter.

   Can’t find a command? Some commands may be hidden in slideout panels in the Ribbon interface. Many Ribbon panels display a down-facing arrowhead beside the name of the panel. Click the arrowhead to see a collection of related but less-used commands. Still can’t find the command? Some Ribbon command buttons may be hidden under others in the same category. AutoCAD remembers the last one you used. For example, you may find POLygon under RECtangle or vice versa.

   AutoCAD starts the RECtang command and prompts you to specify a point for one corner of the rectangle. The command line displays the prompt:

   Specify first corner point or [Chamfer/Elevation/Fillet/Thickness/Width]:

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

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

   AutoCAD prompts you to specify the corner of the rectangle that’s diagonally opposite from the first one.

   Specify other corner point or [Area/Dimensions/Rotation]:

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

   The rectangle is drawn after you specify the second corner point.

   If you know the size of the rectangle that you want to draw (for example, 100 units long x 75 units high), type D to enter the Dimensions option, and then simply type the width and height. Pick a point to indicate which of the four possible alignments you want, and AutoCAD draws the rectangle.

Choosing 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 wherein all sides and angles are equal. The command has nothing to do with missing parrots.

The following steps show you how to use the POLygon command:

1. Click Polygon from the Rectangle drop-down list on the Draw panel of the Home tab, or type POL and press Enter.

   AutoCAD starts the POLygon command and prompts you to enter the number of sides for the polygon.

   Enter number of sides <4>:

2. Type the number of sides for the polygon that you want to draw and then press Enter.

   Your polygon can have from 3 to 1,024 sides.

   AutoCAD 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 the length of one side instead of the center and then the radius of an imaginary inscribed or circumscribed circle. The imaginary circle method is much more common.

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

   After you specify the center point, nothing happens in the graphics area but the command line prompts you to specify whether the polygon is inscribed in an imaginary circle whose radius you specify in Step 5 (the corners touch the circumference of the circle) or circumscribed about the circle (the sides are tangent to the circle).

   Enter an option [Inscribed in circle/Circumscribed about circle] <I>:

4. Type I (for inscribed) or C (for circumscribed), and press Enter.

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

   Specify radius of circle:

5. 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 Mode turned on, the polygon will align orthogonally. I cover using Ortho Mode in Chapter 8.

Rectangles and polygons aren’t special object types. They’re simply regular polylines that have been constructed by special command macros.

Figure 6-4 shows the results of drawing plenty of polygons — a practice known as polygony, which, as far as I know, is legal nearly everywhere.