In this paper, an effective algorithm based on improved time-domain averaging is proposed to detect tool flute breakage during end milling using feed-motor current signatures. The algorithm proposed is demonstrated to be effective in detecting tool flute breakage in real time through a series of milling experiments, and is also demonstrated to be insensitive to the effects for transients, such as cutter runout, entry/exit cuts, and noise in the feed-motor current signals. Results indicated that the approach showed excellent potential for practical, on-line application for tool flute breakage detection during end milling.