of the arrangement and the shape of cutting chips the high speed of chip flow and the marked difference in velocity depending on radial positions would contribute to the overall easy discharge of the chips this can be made possible mainly by virtue of the structure involving much longer tips than corresponding conventional ones suction of air is improved and premature falling out of cutting tips as the result of thermal oxidation or carbonization due to friction heat during cutting operation is avoided since the mounting opening for mounting the output end of the tool transmitting motive power is located in the center and suction holes bounded by the sides inclined inwardly of the shank are arranged on the bottom of the shank in a uniform manner throughout the circumference thus the air can be sucked through the suction holes positioned slantingly in conformity with the direction of rotation during the rotation of the shank to thereby enhance the cooling effect and the cutting performance the segments which consist of two kinds of members that is the long tips and the short tips are arranged so as to be larger in area in the vicinity of the outer boundary of the disk shank than in the region close to the core as a result uniform wear of tips is attained and stable cutting work can be expected to give a smooth and neat cutting surface of the material being cut other important advantages and characteristics which were already elucidated fully are.