In this study, the effects of cutting parameters, boring tool material and the overhang ratio of boring tool (tool clamping length) on the deviation from circularity of a bored hole were examined experimentally The optimal cutting condition can be estimated by the analysis of the signal to noise (S/N) ratio in Taguchi method. The individual contributions of each factor on the deviation from circularity were calculated by using the Analysis of Variance (ANOVA). Therefore, at the determined condition, it could be observed whether a factor is significant or not. Also, it was observed that the values of deviation from circularity increased significantly with an increase in the effective tool length at the lower depth of cut values. In addition, the circularity could be improved with increasing the depth of cut values for the same tool clamping lengths. (C) 2010 Journal of Mechanical Engineering. All rights reserved.