Copyright Goodheart-Willcox Co., Inc. 140 AutoCAD and Its Applications—Advanced Revolving Surfaces from Objects with Dimensional Constraints When constructing a revolved surface, the Expression option of the REVOLVE command can be used with dimensional constraints in the same manner as when using the EXTRUDE command. Examples of mathematical expressions used with constraints are shown in Figures 6-13 and 6-14. These examples illustrate how linear and angular dimensional constraints can be used to calculate an angular value for a revolved surface. The profi le in Figure 6-13A is to be revolved at an angle that is one-half that of the angular dimension (ang2). This is achieved by selecting the Expression option and then entering: ang2/2 As shown in Figure 6-13B, the height of the model changes when the angular dimen- sion is changed. In Figure 6-14, the same 2D geometry is used. However, the aligned dimension d2 is used to create a negative value to revolve the object below the XY plane. The following formula is entered: d2–31 The result of subtracting 31 from the value of d2 is processed as the angular value for the revolution. The result is shown in Figure 6-14. B A Figure 6-13. A—The 2D profile is to be revolved at an angle that is one- half of the angular dimension ang2. B—The revolved surface is created using an expression that references the angular dimension ang2. When the angle is changed, the height changes to maintain the relationship. Figure 6-14. The surface is created using a negative value based on the dimensional constraint d2 to revolve the object below the XY plane.