A robust design for torque optimization of brushless DC spindle motors applied in a hard disk drive, using the Taguchi method, is described and illustrated in this paper. The optimal design process takes into consideration noises that arise in the manufacturing process, such as manufacturing tolerances for the stator tooth shape and variation of the rotor magnet magnetization distribution due to the magnetization fixture and process. The objective of the optimal design using the combined Taguchi's design of experiment (DOE) and finite-element analysis (FEA) approach is to ensure that the spindle motor torque performance is insensitive to the noise, with moderate computational effort. The optimization is realized by a simulation and analysis tool that integrates Taguchi's DOE with the FEA. In this paper, the design optimization process is described and the results are presented.