Analysis of CMM Accuracy in the Measurement of Roundness

In the paper, the possibility and accuracy of the roundness measurement with CMM (Coordinate Measuring Machines) has been analyzed. The accuracy of final measurement result is always affected by many factors and conditions of measurement. The following factors underwent discussion: the form deviation and tolerance of measured detail, and the measuring method determined by the number of measuring points, fitting element and uncertainty of CMM. The results of simulations and measurement have proved that the minimal number of measuring points (4 for circle measurement) is not enough. In order to achieve satisfactory results of the roundness measurement, the number of measuring points should be sufficiently increased. On the other hand, the unlimited increase of the points does not improve the measurements results, but extend the time of measurement. The recommendations on the number of measuring points and the required uncertainty of CMM have been presented, too.