Study on measurement of axisymmetrical form generated by ultra-precision machining (2nd Report) - Check of the accuracy in measuring flat form and spherical form

The purpose of the study is to measure axisymmetrical form, such as flat, spherical, and aspherical surfaces, by using a contact type form measuring equipment and to evaluate three dimensional form deviations. In the previous paper, the following process of the measurement was described; (1) Sectional curves along concentric circles and diameters are measured. (2) These sectional curves are combined on cross points by the least square method to compensate measuring errors due to tilts and lifts of a specimen. (3) A curved surface is generated by interpolation from sectional curves. In this paper, the accuracy of the experimental equipments is made clear by using an optical flat surface and a glass master sphere. The following facts are revealed by some experiments. (1) The accuracy in flatness measurement within a diameter of 42 mm is about 70 nm. (2) If a tilt of a tangent to a sphere is within 25°, the accuracy in the form measurement is about 110 nm.