Development of Ultra High Precision Bearing Mechanisms

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In the precision measurring instruments and dividing machines polygonal shafts and holes have been used to make specially-made bearing mechanisms. In the bearing mechanisms of the famous "TALYROUND", spherical shape for lower part and three-point-contact type for upper part are used. These polygonal shapes are good for vibration characteristics and anti-whirling. Lapping has been used as a finishing mechanism to improve roundness accuracy of cylindrical shafts and holes. However, little has been published on the theoretical analysis of the finishing mechanism for high precision polygonal cross sections. This research offers two methods for finishing polygonal holes, whose shapes are ellipsoidal, triangular, four-protrusion and so on. By one method, the amplitude of the interest Fourier component of out-of-roundness keep constant, while the other components are decreased, using "regular polygonal lap". By the other method, the amplitude can be increased for any Fourier component using special types of lapping tools produced by applying the "Tripod" roundness measuring method. Using one of the tripod lapping tools, the magnitude for the four-protrusion component was increased from 7.64mum to 8.27mum, while the other components were decreased. Out-of-roundness improved from about 40mum to about 30mum. This study shows that any component of the out-of-roundness can be increased, based on a theoretical analysis, as a result many improvements on the new lapping methods, called "tripod lap".