Variation of Form Error of Workpiece held in Chuck in Turning

The variation of error of cylindrical form is investigated experimentally in the turning of workpieces held in chuck under the conditions arranged not to be influenced by the amount of the skill of operators. The experiment consists of such four kinds of tests as turning of brass workpieces in nine kinds of size under the same conditions at six local laboratories, turning of nine workpieces of carbon steel or cast iron at each laboratory for the comparison with brass, turning of nine brass workpieces at fourteen lathes used in six factories by an operator, and replication of the turning every several months on one of the lathes used in the first test. The results are as follows: (1) The form error of workpieces is influenced by dimension and material of workpieces, and, moreover, influenced considerably by the characteristics of lathes, which give different effects individually on the form error of workpieces. (2) The variation of diameters of workpiece along axis sometimes exceeds 20 μm, the tolerance in the Japanese Industrial Standard (JIS), even if the accuracy of the lathe satisfies the test code specified in JIS. (3) In the replication, the variation of diameters of workpieces shows a larger value than the tolerance. (4) Some of the lathes in the factories produce a large variation of diameter of workpieces. Therefore, it is important to maintain the accuracy of lathes and it is necessary to grade lathes by the tests of the machining accuracy.