Abstract: The tool (1) according to the invention is equipped with cutting inserts (5) made of polycrystalline diamond and with washing channels cooling the tool from the inside and discharging, through outlet holes (15), jets of compressed air that remove the highly abrasive powders produced during machining from the cutting areas. In this manner, the tool undergoes less abrasion and anyway it can be sufficiently cooled. The particular choice of the material of the cutting inserts makes the tool more abrasion resistant, while conferring it in the whole a longer operating life. The invention also concerns a method of milling composite materials.