Abstract: Relationships between the cutting tool life T,are analyzed when tangential force Fz and the cutting speed v machining steel EX30 using carbide end mill NT5 at high cutting speeds of 300 to 785 meters per minute. The tool-wear curves and relative T-v curves are shown. Further, the relationships and corresponding curves between Fz and v, feed speed vf and cutting depth ap respectively are also given. These relations and regularities are analysed and discussed concerning the underlying cutting mechanism.