This paper treats the most general chatter vibrations of machine tool or work originating by regenerative effect having an arbitrary overlap factor, by wave cutting effect (time lag of thrust force upon chip thickness fluctuation as varied by relative motion between tool and work), and by wave removing effect (time lead of shearing area upon chip thickness fluctuation through a previous cut). The new concept of “equivalent time lag of thrust force,” containing both any overlap factor and time lag of thrust force, is introduced, and by it, the cutting limit of absolute stability free from chatter can be obtained very easily. Moreover, this concept is verified to be very effective as a stability criterion for regenerative chatter with an unsymmetrical boring bar.