325 Chapter 8 Position Tolerancing Fundamentals Copyright Goodheart-Willcox Co., Inc. The limits of size are separately evaluated and must meet the size requirements. When using the surface method, the sides of the slot may be in any condition provided the limits of size are met and the sides of the slot do not violate the virtual condition boundary. For a slot, the virtual condition is equal to the MMC minus the position tolerance. In the fi rst example shown in Figure 8-37, the virtual condition boundary is .724″. When using the axis (center plane) method, the tolerance zone for the slot center plane is a rectan- gular zone .016″ wide when the feature is at MMC. The tolerance zone is centered on datum plane A. The tolerance zone is equal in height to the slot and extends the full length of the slot. The center plane of the slot is the center plane of the unrelated actual mating envelope of the slot. The center plane must fall inside the tolerance zone. The tolerance zone is .016″ wide when the unrelated actual mating enve- lope is equal to the MMC limit of size. As the size of the unrelated actual mating envelope departs from MMC, additional tolerance equal to the departure from MMC is applicable. Position Tolerance at RFS on a Slot When a position tolerance is applied RFS on a slot, the allowable tolerance is not affected by the size of the toleranced feature. See Figure 8-38. When a position tolerance is applicable at RFS, only the axis method of verifi cation may be used. In the given example, the tolerance zone has a fi xed width of .016″. The center plane of the slot must be within the tolerance zone. The center plane of the slot is defi ned as the center plane of the unrelated actual mating envelope. Bounded Feature A position tolerance may be applied to a bounded feature that has a profi le tolerance applied to it. The profi le tolerance establishes a maximum material boundary, and the position tolerance is used to defi ne the allowable location variation for the maximum material boundary. See Figure 8-39. Profi le tolerances are explained in another chapter. The position tolerance value shown in the feature control frame is a total width tolerance. The .010″ position tolerance creates a virtual condi- tion boundary that is .010″ smaller than the distance across the boundary created by the profi le tolerance. Datum plane A Center plane of slot .016 Tolerance zone RFS Actual mating envelope Goodheart-Willcox Publisher Figure 8-38. A position tolerance applied at RFS to a width feature of size creates a rectangular tolerance zone that controls the feature’s center plane location. .020 Profile zone .005 Position boundary True profile Position boundary Maximum material boundary (created by the profile tolerance boundary) Goodheart-Willcox Publisher Figure 8-39. A position tolerance may be applied to defi ne the position requirement of a bounded feature when a profi le tolerance creates an inner and outer boundary.