Copyright Goodheart-Willcox Co., Inc. 138 AutoCAD and Its Applications—Advanced Revolving Regions Earlier in this chapter, you learned that regions can be extruded. In this manner, holes, slots, keyways, etc., can be created. Regions can also be revolved. A complex 2D shape can be created using Boolean operations on regions. Then, the region can be revolved. One advan- tage of this method is it may be easier to create a region than trying to create a complex 2D profi le as a single, closed polyline. As previously discussed, you can use the Mode option of the REVOLVE command to set the output type to solid or surface. Revolving Surfaces Just as planar and nonplanar surfaces can be extruded, they can also be revolved. When the REVOLVE command is selected, simply pick the surface when prompted to select objects. The surface can be revolved about an axis defi ned by two pick points, an object, or the X, Y, or Z axis of the current UCS. As previously discussed, you can use the Mode option of the REVOLVE command to set the output type to solid or surface. PROFESSIONAL TIP PROFESSIONAL TIP You can also revolve a face on an existing solid or surface into a new solid or surface. The Mode option of the REVOLVE command allows you to set the output type to solid or surface. When prompted to select objects, press the [Ctrl] key and pick the face to revolve. Subobject editing is covered in detail in Chapter 11. Using Extrude and Revolve to Using Extrude and Revolve to Create Surfaces Create Surfaces When creating an extruded or revolved model as a surface, the SURFACEMODELINGMODE system variable controls the type of surface created. The default setting of 0 creates a procedural surface. This is a standard surface composed of multiple fl at polygons, but it has no control vertices. By default, this type of surface is associated with the object used to create it. The SURFACEASSOCIATIVITY system variable controls this setting. A NURBS surface can be created by setting the SURFACEMODELINGMODE system variable to a value of 1. A NURBS surface is composed of splines and contains control vertices that enable the control of the curve shape with great precision. Y axis origin Y axis origin A B Figure 6-10. A—A solid is created using the Y axis as the axis of revolution. B—A different object is created by changing the UCS origin.