Copyright Goodheart-Willcox Co., Inc. 132 AutoCAD and Its Applications—Advanced height. If a pictorial view is displayed, you can move the cursor to establish a specifi c height. The height is always applied along the Z axis of the selected object, not the current UCS. A positive value extrudes the height above the XY plane of the object. A negative height value extrudes the height below the XY plane. If a pictorial view is displayed, you can drag the mouse to set the extrusion above or below the XY plane and then enter the height value. The Direction option provides an alternate way to create the extrusion. After selecting this option, specify a start and end point to defi ne the extrusion direction and height. This is similar to extruding along a path, discussed in the next section. Before entering a height, you can specify a taper angle. The taper angle can be any value between +90° and –90°. A positive angle tapers to the inside of the object from the base. A negative angle tapers to the outside of the object from the base. See Figure 6-2. However, the taper angle cannot result in edges that “fold into” the extruded object. If the command is selected from the Solid tab in the ribbon, the mode is automatically set to solid. However, if an open profi le is selected, a surface is still created. If the command is selected from the Surface tab in the ribbon, the mode is automatically set to surface. In either case, you can use the Mode option to change the output type to solid or surface. Keep in mind, objects that are not closed, such as lines and polylines, always result in extruded surfaces. A solid can only be created by the EXTRUDE command if the original object is closed. NOTE NOTE If a surface is created using the EXTRUDE command, the type of surface created is controlled by the SURFACEMODELINGMODE system variable. The settings available are discussed later in this chapter. PROFESSIONAL TIP PROFESSIONAL TIP Objects such as polylines, lines, and arcs that have a thickness can be converted to surfaces using the CONVTOSURFACE command. Circles and closed polylines with a thickness can be converted to solids using the CONVTOSOLID command. The thickness property for an object is controlled by the Thickness setting in the Properties palette. Figure 6-1. The EXTRUDE command creates a 3D solid or surface from a profile object. A—The initial, closed profile. B—The extruded solid object shown with hidden lines removed. Height A B A B Figure 6-2. A—A positive angle tapers to the inside of the object from the base. B—A negative angle tapers to the outside of the object.