Calibration of Radius Masters Using CMM

Some of the artifacts used extensively as calibration masters for precision measuring instruments are made up of accurate spherical surfaces. In some of such artifacts, only a small portion of sphere is exposed (coverage area) where the diametrical methods can't be used for calibration. In addition, some of the optical elements with spherical surfaces having large radius of curvature present only small area for measurement. The methodology adopted in measuring such spherical surfaces and effect of coverage area on the accuracy of measurements along with associated uncertainty of measurement (UOM) are investigated and discussed in this paper.