In machining processes, current fault diagnosis practice is limit value checking approach, i.e., taking key feature measurements after each machining operation and comparing the measurements with given specifications. The disadvantages are:
• Gauging cost and effort could be very high for complicate processes and products. High redundancy may exist and it is not analyzed. Gauging planning is more based on experiences.
• The data exploration is less effective with little analysis of variation transmission. Therefore it is also hard to do fault diagnosis, i.e., distinguishing error sources among incoming workpiece, machine tools, and fixtures. As a result, less information is provided for variation reductions and for product and process design.