Harmonic Analysis by Spherical Function for Evaluating Form Error of Spherical Parts

A method for measuring the form error of spherical parts, for example, the steel ball used in a bearing assembly, was developed in the previous paper. The measured result showed that the steel balls usually had a form error with three or four undulations. In the present report, a harmonic analysis by the spherical function is introduced to evaluate the sphericities of the steel balls. The "spherical spectrum" defined in this paper has invariant values for each ball, even if the measuring coordinate axes are changed. Steel balls which are sampled in various stages of different finishing processes are measured and the spherical spectrum is calculated.