Composite Feature Control Flashcards

In a composite position feature control frame, what is the primary function of the lower segment, also known as the Feature-Relating Tolerance Zone Framework (FRTZF)?

Answer: It refines the orientation of the pattern to any datums repeated from the upper segment and controls the feature-to-feature relationship.

The lower segment (FRTZF) of a composite control refines the tolerance applied by the upper segment. Its primary role is to control the relationship between the features within the pattern (feature-to-feature location) and to refine the orientation of the entire pattern relative to any datums that are repeated from the upper segment. It does not control the location of the pattern to the datums.

A composite profile tolerance is applied to a surface. The upper segment specifies a tolerance of 0.8 mm to datums |A|B|C|. The lower segment specifies a tolerance of 0.2 mm to datum |A|. How does the lower segment constrain the tolerance zone?

Answer: It creates a 0.2 mm wide tolerance zone that is only constrained in orientation (perpendicularity) to datum A.

In a composite profile tolerance, any datum referenced in the lower segment only controls the orientation of the Feature-Relating Tolerance Zone Framework (FRTZF). The FRTZF is free to translate relative to the datums. Therefore, referencing datum A in the lower segment constrains the rotational degrees of freedom relative to A but does not control the location.

Which of the following statements correctly describes the key difference between a composite position tolerance and a two single-segment position tolerance?

Answer: In a composite tolerance, the lower segment only controls orientation to datums, while in a two single-segment callout, the lower segment controls both location and orientation to its specified datums.

The fundamental difference lies in the function of the lower frame. In a composite tolerance, the lower segment (FRTZF) refines the feature-to-feature relationship and is only constrained in orientation by any repeated datums. In a two single-segment callout, each frame is independent, and the lower frame acts as a separate requirement, controlling both location and orientation with respect to its own datum reference frame.

A designer needs to control a pattern of four mounting holes. The location of the entire pattern on the part has a generous tolerance (e.g., 1.0 mm), but the spacing between the holes must be held to a much tighter tolerance (e.g., 0.1 mm) to ensure a mating part fits correctly. Which GD&T callout is most appropriate for this scenario?

Answer: A composite position tolerance with Ø1.0 mm in the upper segment and Ø0.1 mm in the lower segment.

This is a classic application for composite tolerancing. The upper segment, called the Pattern-Locating Tolerance Zone Framework (PLTZF), controls the location of the overall pattern with the larger tolerance (1.0 mm). The lower segment, the Feature-Relating Tolerance Zone Framework (FRTZF), controls the tighter feature-to-feature relationship (0.1 mm).

When interpreting a composite feature control frame, what is the term for the tolerance zone defined by the upper segment?

Answer: Pattern-Locating Tolerance Zone Framework (PLTZF)

According to the ASME Y14.5 standard, the upper segment of a composite feature control frame establishes the Pattern-Locating Tolerance Zone Framework (PLTZF). This framework controls the location of the entire pattern of features as a group relative to the specified datums. The lower segment establishes the Feature-Relating Tolerance Zone Framework (FRTZF).

In a composite position tolerance, if the primary datum is repeated in the lower segment, but the secondary and tertiary datums are omitted, what is the effect on the Feature-Relating Tolerance Zone Framework (FRTZF)?

Answer: The FRTZF is constrained in orientation to the primary datum but is free to translate and rotate relative to the secondary and tertiary datums.

When datums are repeated in the lower segment of a composite control, they only constrain orientation. By referencing only the primary datum, the FRTZF (the tighter group of tolerance zones) must maintain its orientation to that datum, but it is free to translate and rotate within the constraints of the larger PLTZF, as it is not locked down by the secondary and tertiary datums.