To control the profile of a line or surface, what may be required?

• A. A datum surface
• B. A checking gauge
• C. A list of dimensions
• D. A verification sketch

Answer: (A)

To control the profile of a line or surface in geometric dimensioning and tolerancing (GD&T), a datum surface is essential. The function of a datum is to provide a reference point or surface from which measurements can be taken. When controlling the profile, the profile tolerance is typically defined relative to one or more datum features to ensure the part conforms correctly to the design intent.

Using a datum establishes a controlled geometric relationship for the profile, allowing for consistent measurement and verification of the part's features. This helps prevent variations that could arise from different reference points or misalignments during measurement. For instance, if the profile of a line is being specified, the datum surface helps ensure that the line is measured in a standardized way that reflects its intended position and orientation in three-dimensional space.

While checking gauges, lists of dimensions, and verification sketches can aid in the inspection process, they do not inherently establish the necessary reference framework that a datum surface provides for profile control. Therefore, a datum surface is crucial for accurately defining and maintaining the profile of a line or surface in engineering drawings.