Glass materials have been widely used in optical components in recent years. The purpose of this study was to develop an effective method for real-time detection of the state of cutting tools used in end milling of hard brittle materials. Cutting tests were performed to identify parameters that are useful in monitoring micro tool wear in glass milling. A specific component of the cutting force was found to be related to the progression of tool wear. Furthermore, using fast Fourier transform (FFT) analysis, the peak amplitudes of the cutting forces were found to occur at a specific frequency.