layer thickness shown in table 6 were vapor deposited on the each of the cutting tool bodies by the above described process surface coated end mills of the invention hereafter referred to as coated end mills of the invention 1 8 were produced as surface coated cutting tools according to the invention in addition as a comparative example the above described cutting tool bodies end mills c 1 to c 8 were subjected to ultrasonic cleaning in acetone bath after drying the cutting tool bodies were placed in a deposition apparatus shown in fig3 under the same conditions as example 1 the hard coating layer comprising the ti al n layer having the target composition and the target layer thickness shown in table 6 was vapor deposited on each of the cutting tool bodies by the above described process conventional surface coated end mills hereafter referred to as conventional coated end mills 1 to 8 were produced as conventional surface coated cutting tools next the above described coated end mills 1 to 8 of the invention and conventional coated end mills 1 to 8 were applied to the cutting tests the coated end mills 1 to 3 of the invention and comparative coated end mills 1 to 3 were applied to high speed dry slotting of a high si al u2014 si system alloy under.