Roundness modeling of machined parts for tolerance analysis

Out-of-roundness of circular and cylindrical parts can greatly affect assem bly accuracy. At present, the ASME Y14.5M-1994 specifies circularity tolera nce based on two extreme circular boundaries to confine the highest peak an d the lowest valley of a roundness profile; however, the profile variations within the two extreme boundaries are not accounted for. In this paper, we propose a harmonic roundness model using Fourier series expansion. In addi tion, a cutting profile model has been developed to illustrate the relation ship between the radial error motion of a spindle and the resultant part pr ofile. This relationship is then used to provide physical meanings to the h armonics generated by the proposed roundness model for a part profile, in p articular those caused by fractional frequency spindle error motions. The p roposed harmonic model has been verified statistically by a large number of real profiles produced by both turning and cylindrical grinding processes. The proposed roundness model is expected to provide insights into the adva nced tolerance analysis of circular and cylindrical parts. (C) 2000 Elsevie r Science Inc. All rights reserved.