High-precision measurement of small balls

Spindle compensating high-precision roundness techniques have the resolution required for measuring modern precision miniature workpieces but their accuracy has been considered only at radii of tens of millimetres. As the performance of such instruments decreases with decreasing radius, it is not clear that their precision is adequately maintained. An investigation of the sources of systematic error shows that current designs are usable, in this context, down to radii of around 1 mm. An implementation using a calliperlike stylus on a turntable roundness instrument is described and evaluated on balls of this size.