Which statement best describes how straightness tolerance is inspected?

Which statement best describes how straightness tolerance is inspected?

• A. By using a straightedge to check planarity.
• B. By measuring curvature of the feature along its length.
• C. By comparing the feature to a datum only.
• D. By checking the deviation of a straight feature (line or axis) from a true straight line along its length.

Answer: (D)

Straightness tolerance controls how close a straight feature must stay to a true straight line along its length. When inspecting, you look at a line element of the feature (such as the axis of a shaft or a straight run on a surface) and measure its deviation from an ideal straight line that runs along the feature. The allowable deviation forms a tolerance zone, typically a narrow strip or set of parallel lines aligned with that true straight line. If every point along the feature lies within that zone, the feature satisfies straightness. This approach is what the correct statement is getting at because it emphasizes measuring the deviation from a true straight line along the length of the feature. It’s not about planarity of a surface, nor about curvature in general, nor solely about comparing to a datum—though datums can be used as a reference, the essence of straightness is the deviation from an ideal straight line along the feature.

Straightness tolerance controls how close a straight feature must stay to a true straight line along its length. When inspecting, you look at a line element of the feature (such as the axis of a shaft or a straight run on a surface) and measure its deviation from an ideal straight line that runs along the feature. The allowable deviation forms a tolerance zone, typically a narrow strip or set of parallel lines aligned with that true straight line. If every point along the feature lies within that zone, the feature satisfies straightness.

This approach is what the correct statement is getting at because it emphasizes measuring the deviation from a true straight line along the length of the feature. It’s not about planarity of a surface, nor about curvature in general, nor solely about comparing to a datum—though datums can be used as a reference, the essence of straightness is the deviation from an ideal straight line along the feature.