Abstract: The "S" shaped test piece is used to comprehensively detect the machining accuracy of multi-axis machine tools. However, the existence of theoretical cutting error of "S" shaped test piece leads to the deviation of accuracy detection for multi-axis machine tools. Therefore, an effective method to reduce the theoretical cutting error is proposed. Firstly, the uniform double cubic B-splines surface model is applied to establish the "S" shaped test piece model. Furthermore, the distribution of twist angle at the selected three section lines is obtained. Meanwhile, the influence of twist angle on theoretical cutting error of "S" shaped test pieces is analyzed. Then, the optimized single-point offset (OSPO) method is proposed based on the single-point offset (SPO) method. Moreover, the tool path of "S" shaped test piece is generated by CAD/CAM software based on the OSPO method. Finally, the effectiveness of the proposed method is verified by the experiment. Experiment results show that the average theoretical cutting error of "S" shaped test pieces based on the OSPO method is reduced about 50.1% than the SPO method. In addition, the vast majority of theoretical cutting errors based on the OSPO method are approximately less than 0.005 mm, which can be negligible. It is therefore reasonable to conclude that the proposed method here can avoid the influence of theoretical cutting error on the accuracy detection of multi-axis machine tools efficiently. And its basic idea can be applied to other type of test pieces.

Key words: multi-axis machine tools, “S” shaped test piece, theoretical cutting error, twist angle, optimized single-point offset method