Relating CMM data to design specification

The use of the coordinate measuring technique in coordinate measuring machines (CMMs) is a common practice in assessing the geometric characteristics of manufactured parts, but due to lack of unique and unambiguous definitions of geometric tolerances and the implementation details of their assessment criteria, it is becoming increasingly difficult to carry out the assessment tasks. The objectives of this paper are to (i) determine unique and unambiguous definitions of the tolerance of any feature, (ii) establish a definition of the measured sizes of all features, (iii) determine the criteria for establishing datums from measured data points of the measured features, and finally (iv) establish computational techniques for assessing the CMM data against the design specification. The computational geometry based techniques have been exploited to establish the ideal geometric features (as per the design specifications) required in the assessment problem as per the standards. The methodology has been implemented and the example has been presented to validate the computational effectiveness of the approach in the case of the roundness error.