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FIG. 5-18 MULTIPLE PATTERNS OF FEATURES, SEPARATE REQUIREMENTS

the use of a composite feature control frame. See para. 3.4.4 and Fig. 3-22(a). The position symbol is entered once and is applicable to both horizontal segments. Each complete horizontal segment in the feature control frames of Figs. 5-19 and 5-20 may be verified separately, but the lower segment is always a subset of the upper segment.

(a) Pattern-Locating Tolerance Zone Framework (PLTZF). Where composite controls are used, the upper segment is referred to as the pattern-locating control. The PLTZF is located from specified datums by basic dimensions. It specifies the larger positional tolerance for the location of the pattern of features as a group. Applicable datums are specified in a desired order of precedence, and serve to relate the PLTZF to the datum reference frame. See Figs. 5-19(a) and 5-20(a).

\b) Feature-Relating Tolerance Zone Framework (FRTZF). The lower segment is referred to as the feature-relating control. It governs the smaller positional tolerance for each feature within the pattern (feature-to-feature relationship). Basic dimensions used to relate the PLTZF to specified datums are not applicable to the FRTZF. See Figs. 5- 19(b) and 5-20(b). Where datum references are not specified in the lower segment of the composite feature control frame, the FRTZF is free to be located and oriented (shift and/or tilt) within the boundaries established and governed by the PLTZF. If datums are specified in the lower segment, they govern the orientation of the FRTZF relative to the PLTZF. See Figs. 5-19(c) and 5-20(c). Where datum references are specified, one or more of the datums specified in the upper segment of the frame are repeated, as applicable, and in the same order of precedence, to govern the orientation of the FRTZF.

NOTE: If different datums, different datum modifiers, or the same datums in a different order of precedence are specified, this constitutes a different datum reference frame and design requirements. This is not to be specified using the composite positional tolerancing method, since such a requirement no longer represents a liberation-within-given-limits of the FRTZF. A separately-specified feature-relating tolerance, using a second single-segment feature control frame is used, including applicable datums. as an independent requirement. See Fig. 5-28,

5.4.1.1 Primary Datum Repeated in Lower Segment. As can be seen from the sectional view of the tolerance zones in Fig. 5-19(d), since datum plane A has been repeated in the lower segment of the composite feature control frame, the axes of both the PLTZF and FRTZF cylinders are perpendicular

Feature Control Frame Pattern
FIG. &-19 HOLE PATTERNS LOCATED BY COMPOSITE POSITIONAL TOLERANCING

FIRST PART OF CALLOUT MEANS THIS:

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