Role of datums: Are datum surfaces and datum features used as references to control the size, form, orientation, or location of other features on a part?

Introduction / Context:
Datums are foundational in GD&T. They provide a common, repeatable reference from which to control and measure features. This ensures consistency across design, manufacturing, and quality teams.

Given Data / Assumptions:

• Datums are theoretically exact references derived from selected physical features (datum features) on a part.
• Controls such as position, perpendicularity, parallelism, and runout reference datums to define relationships.
• Both manual and automated inspection rely on these references.

Concept / Approach:
By establishing primary, secondary, and tertiary datums, a datum reference frame (DRF) is created. Tolerances applied with respect to this DRF specify exactly how features must align or be located. This makes drawings unambiguous and reproducible, especially when parts interchangeability and assembly fit are critical.

Step-by-Step Solution:
Select stable, accessible features to serve as datum features.Define datums (A, B, C) from these features to build the DRF.Apply GD&T callouts (e.g., position) referencing the appropriate datums.Inspect parts relative to the same DRF to verify conformance.

Verification / Alternative check:
Review any GD&T example: the feature control frame references datums to specify relationships, proving datums control other features.

Why Other Options Are Wrong:
Limiting datums to cylindrical parts, CMM use, or assembly drawings ignores their universal role across part types and inspection methods.

Common Pitfalls:
Choosing small or unstable surfaces as datums; failing to communicate datum precedence; omitting datum identifiers in feature control frames.

Final Answer:
Correct