Zhang, G.A new methodology is developed for the boring bar structural design based on the theory of optimal control. This methodology takes into account the effect of cutting data selection on the boring bar performance in the design stage. For establishing the design criterion, a system performance index is introduced, which is defined as the summation of norm of each harmonic component of the system transfer function at a specified frequency bandwidth. Consequently, the process of minimizing this index is equivalent to an optimal setting of the design variables of the boring bar structure through the transfer function of the boring machining system. A case study of designing a flatted boring bar structure is provided. The process of determining the flat orientation demonstrates the design criterion of keeping the stochastic part of tool vibration during machining at a possibly low level. A rotatable flatted boring bar is designed for this study. Experiments are carried out and the predicted optimal flat orientation is compared with corresponding measured roughness AA values at different orientation settings, showing good agreements.en-USTechnical Report