A study on in-process detection of machining regime in micro-machining of optical glass (BK7) was conducted on ultra-precision lathe with a fast tool servo system. In micro-machining of optical glass, a brittle regime of machining can easily occur due to the wear of the cutting tool edge or change of depth of cut due to the irregularity of the workpiece. Brittle regime of machining must be prevented to keep the workpiece and tools from further breakage and hence an in-process monitoring system is needed. In this study, the following error signal of the fast tool servo is analyzed theoretically and experiments shows that it can be used as the signal for machining condition monitoring. Filtering and monitoring of following error signal based on the fast tool servo model is proposed to eliminate additional sensors. It is shown that the proposed monitoring method has the ability to detect a brittle regime machining status with a reliable speed and accuracy.
