How would you evaluate a feature with a true position tolerance callout that references datums A and B and has a diameter symbol?

How would you evaluate a feature with a true position tolerance callout that references datums A and B and has a diameter symbol?

• A. You check if the feature’s center lies within a cylindrical zone defined by the stated diameter relative to the DRF from datums A and B
• B. You measure only the distance from A to B
• C. You disregard the diameter symbol
• D. You compare the radius to the datum distance

Answer: (A)

The main idea here is how a true-position tolerance with a diameter value works when datums A and B define the DRF. The true-position callout sets a tolerance zone for the feature’s axis that is shaped as a cylinder with a diameter equal to the specified tolerance. This cylindrical zone is located and oriented by the datum reference frame established by datums A and B. To evaluate, you determine where the feature’s axis sits relative to that DRF and check whether the axis lies inside the cylindrical tolerance zone. If the axis stays within the cylinder, the feature passes; if it falls outside, it fails. So, the correct approach is to verify that the feature’s axis lies within a cylinder, whose size is the stated diameter and whose position/orientation is defined by the DRF from datums A and B. This is why simply measuring a distance between datums, disregarding the cylindrical tolerance zone, or ignoring the diameter symbol, or comparing a radius to a datum distance, would not correctly determine compliance.

The main idea here is how a true-position tolerance with a diameter value works when datums A and B define the DRF. The true-position callout sets a tolerance zone for the feature’s axis that is shaped as a cylinder with a diameter equal to the specified tolerance. This cylindrical zone is located and oriented by the datum reference frame established by datums A and B. To evaluate, you determine where the feature’s axis sits relative to that DRF and check whether the axis lies inside the cylindrical tolerance zone. If the axis stays within the cylinder, the feature passes; if it falls outside, it fails.

So, the correct approach is to verify that the feature’s axis lies within a cylinder, whose size is the stated diameter and whose position/orientation is defined by the DRF from datums A and B. This is why simply measuring a distance between datums, disregarding the cylindrical tolerance zone, or ignoring the diameter symbol, or comparing a radius to a datum distance, would not correctly determine compliance.