7.Choose Sphere from the Solids toolbar. At the Specify center of sphere <0,0,0>: prompt, use the Center object snap to pick the center of the cone’s

base. At the Specify radius of sphere or [Diameter]: prompt, type 1 .

8.Type isolines . Set the new value to 8. Do a regen to see the result.

9.Choose Zoom Extents from the Zoom flyout of the Standard toolbar.

10.Do a hide. Notice the objects appear realistic, regardless of the ISOLINES setting.

11.Save your drawing. It should look like Figure 24-8.

Figure 24-8: The four solids.

Creating Extruded Solids

The EXTRUDE command creates solids from closed 2D objects. The result is similar to adding thickness to a 2D object (discussed in Chapter 21) or using the TABSURF command (see Chapter 23), except that you get a solid instead of a surface.

You can extrude closed 2D polylines, circles, ellipses, closed splines, donuts, and regions. You can use the REGION command to create one object from several objects for this purpose. You can select several objects and extrude them at one time. Figure 24-9 shows several extruded solids.

Tip The DELOBJ system variable determines whether objects used by EXTRUDE to make other objects are retained. By default, they’re deleted. Therefore, when you use a 2D object to make a solid, the 2D object is deleted. If you make a mistake during extrusion and notice it later — after it’s impractical to undo several commands you want to keep — when you erase the solid, you have no 2D object to use to re-create the solid. (You can put such objects on a layer that can be turned off, in case you need them again.) Set DELOBJ to 0 (zero) to keep objects used to create other objects. On the other hand, if you’re sure about what you’re doing, keeping DELOBJ at 1 avoids having to erase unwanted 2D objects in your drawing.

When you extrude an object, by default you extrude it perpendicular to the object. However, you can also taper the extrusion, as in the extruded rectangle in Figure 24-9. The angle is

702 Part IV Drawing in Three Dimensions

measured so that a positive angle tapers the object inward. A negative angle tapers the object outward so it gets wider as it extrudes.

Note Don’t taper the object too much. If the taper angle results in the object coming to a point before its full height, AutoCAD cannot create the solid.

Figure 24-9: Some extruded solids.

You can extrude the object along a path. A path can be a line, circle, arc, ellipse, elliptical arc, polyline, or a spline. The path object must be in a different plane than the original object. Figure 24-10 shows a circle extruded along an arc.

Original circle Arc used as path for extrusion

Figure 24-10: A circle extruded along an arc.

Not all paths are suitable for extruding objects. In the following situations, the extrusion may not work. The path should not be:

Too close to the original object’s plane

Too complex

Too tightly curved or bent for the size of the original object

Here are the steps for creating an extruded solid:

STEP-BY-STEP: Creating Extruded Solids

1.Open ab24-a.dwg from the CD-ROM.

2.Save the file as ab24-02.dwg in your AutoCAD Bible folder. If the Solids toolbar is not displayed, right-click any toolbar and choose Solids. Make sure OSNAP is on. Set running object snaps for endpoint and midpoint. This is a small mounting angle, shown in an edge view.

3.The angle is made up of lines and arcs. To extrude it, you need to change it into a polyline or region. To change it into a polyline, choose Modify Object Polyline. Follow the prompts:

Select polyline or [Multiple]: Select any object on the angle. Object selected is not a polyline

Do you want to turn it into one? <Y> Right-click.

Enter an option [Close/Join/Width/Edit vertex/Fit/Spline/Decurve/ Ltype gen/Undo]: Right-click and choose Join.

Select objects: Use a window to select all the objects in the angle.

Select objects: Right-click. 6 segments added to polyline

Enter an option [Open/Join/Width/Edit vertex/Fit/Spline/Decurve/Ltype gen/Undo]: Right-click and choose Enter.

4.Choose Extrude from the Solids toolbar. Select the mounting angle, and then

right-click to end object selection. At the Specify height of extrusion or [Path]: prompt, type 3 . At the Specify angle of taper for extrusion <0>: prompt, press Enter to accept the default.

5.Choose View 3D Views SE Isometric.

6.Do a hide using the HIDE command.

7.Save your drawing. It should look like Figure 24-11.

704 Part IV Drawing in Three Dimensions

Figure 24-11: The completed mounting angle.

The mounting angle should have two holes in it. You would create the holes using the SUBTRACT command, which is covered later in this chapter.

Drawing Revolved Solids

The REVOLVE command creates solids from closed profiles. (By contrast, the REVSURF command, which creates surfaces, revolves an open profile around an axis.) You can revolve closed 2D polylines, circles, ellipses, closed splines, and regions.

The DELOBJ system variable affects whether the original objects are deleted. The default setting is 1 (delete objects). Set DELOBJ to 0 (zero) to retain the original objects.

Figure 24-12 shows a solid created by revolving a rectangle around a line. You can also create this solid by drawing two circles and extruding them and then subtracting the smaller circle from the larger one — it just depends on which technique you’re more comfortable with.

Figure 24-12: A solid created by revolving a rectangle around a line.