Methods for determining the effect of flatness deviations, eccentricity and pyramidal errors on angle measurements

In angle calibrations the uncertainty contributions of the autocollimator and index table are easily estimated as these uncertainties are well documented, but it is more difficult to determine the uncertainties associated with flatness deviations, eccentricity and pyramidal errors of the measuring faces. Deviations in the flatness of angle surfaces have been held responsible for the lack of agreement in angle comparisons. An investigation has been carried out using a small-angle generator and an autocollimator to determine the effect of flatness deviations of the measuring surfaces on angle measurements. The small-angle generator, together with a translation stage and tilt table, was also used to determine the effect of eccentricity and pyramidal errors. These methods were developed to calculate the related uncertainties associated with flatness deviations, eccentricity and pyramidal errors on face-to-face angle measurements. The results show that flatness and eccentricity deviations have less effect on angle measurements than do pyramidal errors.