How would you handle a pattern of features that must be coaxial with a datum axis?

How would you handle a pattern of features that must be coaxial with a datum axis?

• A. Use a distance tolerance between holes.
• B. Use a symmetrical position tolerance only.
• C. Use a coaxiality tolerance or true position with a datum frame to ensure the pattern’s axes are coaxial with the datum axis.
• D. Use a parallelism tolerance with a reference plane.

Answer: (C)

When several features must share a common axis that is aligned with a given datum axis, you control that alignment with coaxiality or with a true position tied to a datum frame. Coaxiality directly constrains the axis of each circular feature to lie within a cylindrical tolerance zone coaxial with the datum axis, so the pattern’s axes are guaranteed to run on that datum axis. Alternatively, you can use a true position tolerance for the pattern, referenced to a datum frame, to ensure the pattern’s axes align with the datum axis as you specify the tolerance zone around that axis. The other approaches don’t enforce this axial alignment. A distance tolerance between holes only controls spacing, not how their axes relate to the datum axis. A parallelism tolerance to a plane governs orientation relative to that plane, not alignment of all feature axes to a common datum axis. A symmetric position tolerance, by itself, doesn’t ensure coaxiality unless paired with an explicit datum frame and axis control.

When several features must share a common axis that is aligned with a given datum axis, you control that alignment with coaxiality or with a true position tied to a datum frame. Coaxiality directly constrains the axis of each circular feature to lie within a cylindrical tolerance zone coaxial with the datum axis, so the pattern’s axes are guaranteed to run on that datum axis. Alternatively, you can use a true position tolerance for the pattern, referenced to a datum frame, to ensure the pattern’s axes align with the datum axis as you specify the tolerance zone around that axis.

The other approaches don’t enforce this axial alignment. A distance tolerance between holes only controls spacing, not how their axes relate to the datum axis. A parallelism tolerance to a plane governs orientation relative to that plane, not alignment of all feature axes to a common datum axis. A symmetric position tolerance, by itself, doesn’t ensure coaxiality unless paired with an explicit datum frame and axis control.