How do you evaluate a hole's true position relative to two datums A and B?

How do you evaluate a hole's true position relative to two datums A and B?

• A. Use three coordinate measurements
• B. The axis must lie within the cylindrical tolerance zone defined by the true position with respect to datums A and B
• C. Check color
• D. Check weight

Answer: (B)

In GD&T, evaluating a hole’s true position relative to datums means checking whether the hole’s axis falls inside a defined tolerance zone that constrains both location and orientation. For a hole, that tolerance zone is a cylinder whose diameter equals the positional tolerance, and whose axis is oriented by the primary datum and located by the secondary datum (and any others as specified). When two datums A and B are used, the cylindrical zone is defined in the datum reference frame set by A and B, so the axis of the hole must lie within that cylinder. If the hole axis stays inside the cylinder, the hole meets the true-position requirement with respect to those datums. This is the best description because it directly ties the true position concept to a physical, measurable zone—the cylindrical tolerance zone—rather than just raw coordinates or unrelated properties. Color and weight have no bearing on geometric position. Simply taking three coordinate measurements isn’t the GD&T evaluation, since true position is a relation to the datums expressed as a cylindrical zone about the hole axis.

In GD&T, evaluating a hole’s true position relative to datums means checking whether the hole’s axis falls inside a defined tolerance zone that constrains both location and orientation. For a hole, that tolerance zone is a cylinder whose diameter equals the positional tolerance, and whose axis is oriented by the primary datum and located by the secondary datum (and any others as specified). When two datums A and B are used, the cylindrical zone is defined in the datum reference frame set by A and B, so the axis of the hole must lie within that cylinder. If the hole axis stays inside the cylinder, the hole meets the true-position requirement with respect to those datums.

This is the best description because it directly ties the true position concept to a physical, measurable zone—the cylindrical tolerance zone—rather than just raw coordinates or unrelated properties. Color and weight have no bearing on geometric position. Simply taking three coordinate measurements isn’t the GD&T evaluation, since true position is a relation to the datums expressed as a cylindrical zone about the hole axis.