抄録
The tolerance for the pitch diameter of screw threads used for the purpose of fastening includes the components corresponding to the tolerances for pitch and flank angle. This paper describes some statistical considerations on the distributions of the diametral equivalents EP and Eα of the pitch error and flank angle error, and the relation between the tolerance Ts for simple pitch diameter and the cumulative tolerance T for pitch diameter. It is found that the general case on the distributions of EP and Eα is the midway between two extreme cases (a) and (b). In the case (a) the variation from the straight line, which shows the inclination of the cumulative pitch error or the mean deviation of the flank angle error, is negligible. In the case (b) the inclination or deviation of the above mentioned straight line is negligible compared with the variation from the straight line. Assuming that the tolerance for EP and Eα are T/3 respectively, the ratio Ts/T is calculated. It is found that Ts/T is 0.72 for the case (a) and 0.58 for the case (b). If the statistical consideration is not given, the ratio Ts/T is 1/3 under the same condition.
