Uncertainty analysis for roundness measurements by the example of measurements on a glass hemisphere

This paper presents an uncertainty analysis for roundness measurements on a glass hemisphere. The measurements were carried out with the spindle measu ring instrument Talyrond 73. For the correction of spindle errors, a multi- step error separation technique with ten steps was used. Various input quan tities were investigated such as the form deviations of the hemisphere, the characteristic of the probing system and thermal drift effects. Finally, a detailed uncertainty budget was developed. It is shown that the standard u ncertainty for a single profile point is 1.5 nm. This results in a standard uncertainty of u (RONt) = 3 nm for the roundness deviations of the hemisph ere.