299 Chapter 8 Position Tolerancing Fundamentals Copyright Goodheart-Willcox Co., Inc. Material Condition and Material Boundary Modifi er Application Rule #2 of the ASME Y14.5-2018 standard (and previous revisions) requires that all tolerances are applicable RFS and all datum feature references are applicable RMB unless otherwise specifi ed. See Figure 8-5. The maximum material condition (MMC) or least material condition (LMC) modi- fi er must be shown if applicable to the tolerance. The maximum material boundary (MMB) or least material boundary (LMB) modifi er must be shown if applicable to the datum feature reference. Selection of the appropriate modifi ers depends on the design application. Each applicable material condition has a signifi cantly different effect on the requirements of the specifi ed tolerance. The effect of each applicable material condition is explained in this chapter. Where no material boundary modifi er is shown on a datum feature reference, the datum feature ref- erence is understood to apply regardless of material boundary (RMB), meaning at the actual location the feature exists within the material boundaries. If a datum feature reference includes a material bound- ary modifi er (MMB or LMB), the datum feature refer- ence is understood to apply at the specifi ed material boundary. It is simulated at that boundary. A datum feature reference may also be modifi ed to apply at a size or location defi ned by the basic dimension where it is designed or at a specifi c dimension that is shown following the datum reference letter. The specifi ed applicable material boundary for the datum feature references may be different from the specifi ed applicable material condition for the tolerance value. As an example, the tolerance value may be applicable at MMC and the datum feature references applicable RMB. Datum feature references to surfaces should not include the MMB or LMB modifi er unless the surface has a profi le tolerance that establishes material boundaries. Position Tolerance Zone A position tolerance zone will usually have a defi ned shape, size, location, and orientation. See Figure 8-6. The shape is generally determined by whether or not a diameter symbol is placed in the feature control frame. The three-dimensional size of the tolerance zone is typically defi ned by the toler- ance value shown in the feature control frame and by the length of the hole (or whatever feature of size is being controlled). Basic dimensions and references to datum features defi ne the location and orientation requirements for the tolerance zone. In undimensioned models, the digital defi ni- tion of the geometry establishes feature dimensions, including angles. The location and orientation data can be noted as basic when a position tolerance is applied to a feature. In orthographic views, holes that appear per- pendicular to a feature are understood by drawing convention to be at a basic 90° angle. Orientation (angle) dimensions may be used to specify any required angle. Any angle other than 90° must be dimensioned. A typical position tolerance specifi cation and the resulting tolerance zone are shown in Figure 8-6. The shape, size, location, and orientation of the RFS assumed unless MMC or LMC is shown RMB, MMB, or LMB is applicable when referencing a datum feature of size or a bounded feature Basic or a basic value may be specified Goodheart-Willcox Publisher Figure 8-5. Regardless of feature size is assumed on position tolerances. Other applicable modifi ers must be shown. Tolerance zone extends the full length of the hole Tolerance zone perpendicular to datum A True position (location) Ø.024 When at MMC Ø.601 Virtual condition Datum A Goodheart-Willcox Publisher Figure 8-6. The position tolerance zone and virtual condition for a hole are cylindrical and extend the full length of the hole unless specifi ed otherwise.