Copyright Goodheart-Willcox Co., Inc. 206 AutoCAD and Its Applications—Advanced O-Ring Groove An O-ring is a circular seal that resembles a torus. It sits inside of a groove constructed so that part of the O-ring is above the surface. An O-ring groove can be constructed by placing the center of a circle on the outside surface of a cylinder. Then, revolve the circle around the cylinder. Finally, subtract the revolved solid from the cylinder. 1. Construct the cylinder to the required dimensions, Figure 8-34A. 2. Rotate the UCS on the X axis (or appropriate axis). 3. Draw a circle with a center point on the surface of the cylinder, Figure 8-34B. 4. Revolve the circle 360° about the center of the cylinder, Figure 8-34C. 5. Subtract the revolved object from the cylinder, Figure 8-34D. PROFESSIONAL TIP PROFESSIONAL TIP In many cases, you will draw the O-ring as a torus. A copy of the torus can be used to create the O-ring groove instead of revolving a circle as described in the previous section. Architectural Molding Architectural molding features can be quickly constructed using extrusions. First, construct the profi le of the molding as a closed shape, Figure 8-35A. Then, extrude the profi le the desired length, Figure 8-35B. A B C D Figure 8-33. Constructing a boss. A—Draw a cylinder for the hole so it extends above the surface of the object. B—Draw a cylinder the height of the boss on the top surface of the object. C—Union the large cylinder to the base. Then, subtract the small cylinder (hole) from the unioned objects. D—Fillet the edge to form the boss. A B C D E Figure 8-34. Constructing an O-ring groove. A—Construct a cylinder this one has a round placed on one end. B—Draw a circle centered on the surface of the cylinder. C—Revolve the circle 360° about the center of the cylinder. D—Subtract the revolved object from the cylinder. E—The completed O-ring groove.