In this paper we discuss the deformation analyses of boring bars using analytical and finite-element methods. Three types of circular boring bars with HSS and cemented-carbide properties were selected, and their deformations when subjected to oblique boring forces were calculated using both methods. A guideline is proposed for the manufacturer who can determine the extent of the errors that affect the dimensional tolerance and the surface-finish accuracy of the bored hole produced by the bar bent when subjected to the boring forces. Also, we observed that a conical bar is not an appropriate design for boring a long hole. (C) 2006 Journal of Mechanical Engineering. All rights reserved.