Assessment of circularity error using a selective data partition approach

This paper presents a novel and accurate method to estimate the circularity tolerance of a machined part. The selective data partition (SDP) algorithm presented here utilizes the actual measurement points obtained from a CMM to calculate the circularity tolerance. The tolerance zone obtained by this method conforms to the definition of roundness tolerance as specified in the ANSI (ANSI 1994) standards. The data set is sub-divided into quadrants and the basis points are then chosen from among the points in each quadrant. The basis points are then used to fit a pair of concentric circles with minimum radial separation. The circularity tolerance is given by the difference in the radii of the concentric circles. An iterative procedure is followed to arrive at the final circularity tolerance value. Several data sets were tested to illustrate the successful implementation of the algorithm. The results thus obtained are also compared with the existing methods to demonstrate the accuracy and ease of implementation of this algorithm.