The bending which occurs on a cutting tool during machining on a lathe affects tool life, surface roughness and dimension correctness. In this research, the bending which has been calculated by Castigliano theorem has been compared with the bending obtained by finite element method. Under the constant cutting conditions, material C,1060 has been machined with high speed steel (HSS) lathe cutting tools having 60 degrees, 75 degrees and 90 degrees of cutting edge angle. It was determined by using ANSYS finite elements program that the bending of the cutting tool generated by the forces, which varied between 1360 N and 1325 N and occurred during cutting, varied between 0.039958 and 0.04373 mm. According to the results, it has been observed that the bending that was calculated by Castigliano theorem and that varied between 0.03542 and 0.034505 mm was almost the same with the bending determined by finite elements method. In other words, it was seen that the calculated values approach to the analysed results up to 0.4%. (c) 2004 Elsevier Ltd. All rights reserved.