Repeatability would would be the key issue in using the 90 degree cylindrical surface as a datum. Finding the center of a partial arc of less than 180 degrees is much less reliable than finding the center of an arc greater than 180 deg. The CMM could find the axis with 6 points, but if you...
Dave,
You are correct in your assesment of the hard gage used in the example if it were used to verify the upper segment of the position tolerance for the two threaded holes. The holes in the gage would need to be 10.8 dia for a 10.0 gage pin and datum simulators would be required for datums B...
It is important to remember in this case that runout is a surface control. Datum "D" is an axis perpendicular to datum "C" centered about datum feature "D". Runout controls the surface of the feature relative to the axis, so it is not actually referencing itself.
Robert Bohot
GDTP-S
