Copyright Goodheart-Willcox Co., Inc. Chapter 8 Creating and Working with Solid Model Features 205 Countersink A countersink is like a counterbore with angled sides. The sides allow a fl at-head machine screw or wood screw to sit fl ush with the surface of an object. A countersink can be drawn in one of two ways. You can draw an inverted cone centered on a hole and subtract it from the base or you can chamfer the top edge of a hole. Chamfering is the quickest method. 1. Draw a cylinder representing the diameter of the hole, Figure 8-32A. 2. Subtract the cylinder from the base object. 3. Select the CHAMFEREDGE or CHAMFER command. 4. If using the CHAMFEREDGE command, pick the top edge of the hole and enter the chamfer distance(s). Preview the result before completing the operation, Figure 8-32B. 5. If using the CHAMFER command, select the top edge of the base object, enter the chamfer distance(s), and pick the top edge of the hole. Boss A boss serves the same function as a spotface. However, it is an area raised above the surface of an object. Draw a boss as follows. 1. Draw a cylinder representing the diameter of the hole. Extend it above the base object higher than the boss is to be, Figure 8-33A. 2. Draw a second cylinder the diameter of the boss. Place the base of this cylinder above the top surface of the base object a distance equal to the height of the boss. Give the cylinder a negative height value so that it extends inside of the base object, Figure 8-33B. 3. Union the base object and the second cylinder (boss). Subtract the hole from the unioned object, Figure 8-33C. 4. Fillet the intersection of the boss with the base object, Figure 8-33D. Subtract A B Figure 8-31. Constructing a spotface. A—The bottom of the second, larger-diameter cylinder should be located at the exact depth of the spotface. However, the height may extend above the surface of the base. Then, subtract the two cylinders from the base. B—The finished solid. Edge to chamfer A B Figure 8-32. Constructing a countersink. A— Subtract the cylinder from the base to create the hole. B— Chamfer the top of the hole to create a countersink.