When dimensioning a hole that must be coaxial with a mating feature, what GD&T approach ensures proper location and orientation?

When dimensioning a hole that must be coaxial with a mating feature, what GD&T approach ensures proper location and orientation?

• A. Use a chain dimensioning technique with generalized tolerances.
• B. Use a true position tolerance with a datum feature reference frame to control both location and orientation.
• C. Use a basic dimension without any tolerance.
• D. Use a surface roughness spec.

Answer: (B)

Tying the hole to a defined coordinate system with a true position tolerance is the way to ensure both its location and its orientation relative to the mating feature. By establishing a datum feature reference frame, you create a repeatable origin and orientation for the part. The true position tolerance zone is a cylindrical area around the hole’s axis that is coaxial with that datum frame. To be within tolerance, the hole’s axis must lie inside this cylindrical zone, which means it can’t wander from the intended position and it must stay aligned with the datum axes. This combination directly controls coaxiality with the mating feature because the datums define how the part is oriented, and the axis of the hole must stay within the tolerance zone relative to that frame. The other options don’t provide this integrated control: chaining dimensions with generalized tolerances is vague, a basic dimension offers no tolerance at all, and surface roughness covers finish rather than geometry location or alignment.

Tying the hole to a defined coordinate system with a true position tolerance is the way to ensure both its location and its orientation relative to the mating feature. By establishing a datum feature reference frame, you create a repeatable origin and orientation for the part. The true position tolerance zone is a cylindrical area around the hole’s axis that is coaxial with that datum frame. To be within tolerance, the hole’s axis must lie inside this cylindrical zone, which means it can’t wander from the intended position and it must stay aligned with the datum axes. This combination directly controls coaxiality with the mating feature because the datums define how the part is oriented, and the axis of the hole must stay within the tolerance zone relative to that frame. The other options don’t provide this integrated control: chaining dimensions with generalized tolerances is vague, a basic dimension offers no tolerance at all, and surface roughness covers finish rather than geometry location or alignment.