178 Part II: Let There Be Lines

(Throwing) Curves

Table 9-1 lists the AutoCAD commands for drawing curvy things. It shows you the tool icons found on the Ribbon, toolbars, and menus, and gives the command name with its alias (where one exists) if you like to type. It also tells you where to find or how to enter the commands, using both the Ribbon in the Drafting & Annotation workspace and the Draw toolbar and Draw menu in the AutoCAD Classic environment.

Table 9-1 AutoCAD Drawing Commands for Curved Objects

Slideout panels are part of the Ribbon interface in AutoCAD 2013’s Drafting & Annotation, 3D Basics, and 3D Modeling workspaces. Slideouts are present in panels that show a small down-pointing triangle next to the panel title. To open a slideout, click the panel title bar (for example, Draw on the Home tab). The panel expands downward, and a pushpin icon appears at the left end of the

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panel title bar. After you click a tool button, the slideout panel closes. Click the pushpin in the title bar to pin the panel — that is, force it to stay open.

If you’re familiar with earlier AutoCAD releases, you may suspect that the Draw panel in AutoCAD 2013’s Ribbon interface is also missing some commands. Well, as they used to say in the ’90s, the paradigm has shifted! Those commands are still there, they’ve just been shifted around a bit to make the Ribbon organization more task based.

Going full circle

AutoCAD offers an easy and intuitive 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 specify the radius (the default option) or the diameter. You can also define a circle by choosing one of the following options of the command (for those other ways):

2-Point (2P): Draws a circle where the distance between two specified points is equal to the diameter of the circle. If you’re keyboarding, enter 2P at the command prompt to choose this option; it’s spelled out as 2-Point on tooltips.

3-Point (3P): Draws a circle through any three specified points.

Tangent-Tangent-Radius (Ttr): Draws a circle tangent to two existing drawing objects and a specified radius.

Tangent-Tangent-Tangent: Draws a circle tangent to three valid existing drawing objects. (By valid, we mean it’s mathematically possible to construct a circle tangent to the three selected objects.) Note that you can’t create this kind of circle by typing a command option at the command line because there is no such command option. This method is actually a macro, and you run it by choosing Tan, Tan, Tan from the Circle button menu on the Home tab’s Draw panel.

Figure 9-1 illustrates these six different ways of drawing circles. Whether these additional methods are useful or not 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.

Follow these steps to use the CIRCLE command:

1.Click the Home tab on the Ribbon.

The most frequently used commands in AutoCAD are found on the Ribbon’s Home tab.

2.Set an appropriate layer to be current.

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180 Part II: Let There Be Lines

2 Point 3 Point Tan, Tan, Tan

Figure 9-1: Pi R squared; circles R round, pizzas are flat and round.

3.Click the Circle button on the Ribbon’s Draw panel, or type C and press Enter.

AutoCAD starts the CIRCLE command and prompts you to specify the center point of the circle. If Dynamic Input is toggled on, press the down arrow on your keyboard to see the options at the crosshairs. The command line shows

Specify center point for circle or [3P/2P/Ttr (tan tan radius)]:

The prompts show 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 techniques.

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

Use one of the precision techniques described in Chapter 7 if you’re doing real drafting. Object snap, snap, and typing coordinates all work well for specifying the center point.

AutoCAD 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 two-times tables — or, more seriously, if the diameter is easier to type exactly than the radius is.

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

AutoCAD draws your circle and returns to a blank command prompt. The first point you picked is the center. The command prompt doesn’t tell you so, but if you pick a second point instead of entering a number (or typing D to invoke the Diameter option), AutoCAD interprets the distance between the first and second points as the radius value.

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 onscreen 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 nearly always have to specify arcs more exactly than is possible by using this method. AutoCAD helps you specify such arcs, too — but the procedure ain’t easy.

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 draws arcs in a counterclockwise direction, so pick a start point in a clockwise direction from the endpoint.

After you specify the center and start point, AutoCAD presents several options you can choose, including the following:

Angle: Specifies the included angle that the arc sweeps out. A 180degree angle, for example, is a semicircle.

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

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

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

Center: Prompts you for the arc’s center point and then finishes with the three options listed previously.

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

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

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182 Part II: Let There Be Lines

To get a feel for how these permutations can be strung together to create different arc-drawing methods, click the down arrow beside the Arc tool button on the Ribbon’s Draw panel and look at the drop-down menu that unfurls, as shown in Figure 9-2. Using the Ribbon is also the most direct way of actually using any of these options — at least until you’re really familiar with the program and are adept at entering keyboard shortcuts.

Most problems that beginners (and even many experienced users) have with the ARC command is that they forget that when using many of its options it draws counterclockwise from the start point.

Figure 9-2: A deluge of Arc options, with the results of using some of those options.

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

1.Set an appropriate layer to be current.

2.Click the Arc button on the Home tab’s Draw panel, or type A and press Enter.

AutoCAD starts the ARC command and prompts you to specify the start point of the arc. The command line shows

Specify start point of arc or [Center]:

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

AutoCAD prompts you to specify a second point on the arc.

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