Nicked cutting tool

An end mill cylindrical as a whole having at one end a cutting part and at the other end a shank which is mounted to a rotary driving means, said end mill being suited to cut fiber-reinforced composite materials and comprising:

• an even number of twisted grooves spirally formed on a circumferential surface of said cutting part;
• lands provided between said spiral grooves;
• twisted cutting edges formed along one side of
• a plurality of nicks formed in parallel to each other on said lands, nicks on one of two lands adjacently opposed to each other with one of said twisted grooves therebetween being inclined in one direction relative to an axis of said end mill and nicks on the other one of said two lands adjacently opposed to each other being inclined in another direction which is opposite to said one direction of said nicks on said one land;
• and
• outer sharp edges formed between and parallel to said nicks on said lands, said outer sharp edges on one of two lands adjacently opposed to each other facing a tip end of said cutting part and the outer sharp edges on the other one of said two lands adjacently opposed to each other facing the shank of said end mill;
• wherein when said shank is mounted to said rotary driving means and rotated in one direction without being moved up and down in the axial direction, a cutting up of said materials is performed by said outer sharp edges formed on one of two lands opposed to each other and a cutting down is performed by said outer sharp edge formed on the other one of said two lands.