Tolerances of Roundness and Cylindricity in Machine Parts in Japanese Industry

To standardize the numerical tolerance of cylindrical machine parts with respect to roundness and cylindricity, the tolerances which are actually directed in machine designs in mechanical industry of Japan are investigated by means of questionnaires. 158 answers are obtained. The distinctive relations can not be found out between the tolerances of form errors of machine parts and their dimensions. Then, the answers are classified by machining processes such as cutting, grinding and other special machining, and by industries such as fine instruments, machine tools, industrial machines, transportation machines, optical machines and electrical machines. Geometrical mean values of the tolerances and the dimensions at every five points from the smallest to the largest machine parts are calculated, and running mean values at every five points of the geometrical mean values from the smallest one to the largest are calculated on each classified item individually. As the results, it is distinctly recognized that there are differences between the tolerances of the respective machining processes and also between the tolerances of the respective industries, and that the tolerances are put under such simple rules that the tolerances of roundness and cylindricity versus diameters of machine parts are given by Ai and the tolerances of cylindricity versus length of machine parts are given by Bi2/3 in the case that length over diameter is more than three, where i is the tolerance unit in ISO System of Limits and Fits, iL, is the value given by length instead of diameter in the tolerance unit, and A and B are constants as regard to machineing processes.