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.

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.

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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:

1.Draw the object that you want to extrude. If you want to extrude along a path, draw the path object.

2. Choose Extrude from the Solids toolbar.

3.Select the object or objects to extrude.

4.At the Specify height of extrusion or [Path]: prompt, specify the height of the extrusion or use the Path option to extrude along a path object.

If you specified a height, at the Specify angle of taper for extrusion <0>: prompt, press Enter to extrude with no taper angle or specify a taper angle.

If you chose the Path option, at the Select extrusion path or [Taper angle]: prompt, select the path object.

STEPS: 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 that 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 of 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.Apply the HIDE command.

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

Figure 24-11: The completed mounting angle.

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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.

To create a revolved solid, follow these steps:

1. Choose Revolve from the Solids toolbar.

2.At the Select objects: prompt, select one or more closed objects.

3.At the Specify start point for axis of revolution or define axis by [Object/X (axis)/Y (axis)]: prompt, you can pick two points to create an axis of revolution. You can also select an object as an axis by using a line or one segment of a polyline. Use the X or Y options to revolve the object around the X or Y axes.

4.At the Specify angle of revolution <360>: prompt, press Enter to revolve the object 360 degrees or type an angle, either positive or negative.

As with the REVSURF command, you need to determine the positive direction of rotation if you’re revolving less than 360 degrees. (Of course, it may be quicker to try one way and just do it the other way if it doesn’t turn out right.) Here’s how to figure it out: