Diamond-coated rotary cutting tool

A diamond-coated rotary cutting tool comprising a tool base made of hard metal and a diamond coating covering the surface thereof, wherein

• the tool base is provided with a base rake-face, a base flank-face, and a base cutting-edge part provided on a ridge in which the base rake-face and the base flank-face cross,
• the diamond coating forms:
• a rake-face side diamond coating, comprising a first diamond layer made of minute diamond particles and a second diamond layer made of diamond particles which are larger than the diamond particles of the first diamond layer, wherein the rake-face side diamond coating covers a surface of the base flank-face and has a mean coat thickness d2 not less than 3 μm and not more than 25 μm;
• and a flank-face side diamond coating covering at least a prescribed region of the tool rake-face, wherein a mean coat thickness d1 is a thickness of a smaller range of one of a range not less than 0 μm and not more than 5.0 μm or a range less than the mean coat thickness d2,
• the flank-face side diamond coating is provided with the first diamond layer forming a surface thereof and the second diamond layer adjacent to the first diamond layer at a tool-base side,
• the rake-face side diamond coating is provided on the prescribed region that is at least smaller one of a region 50 μm or 1/10 of a tool diameter from the base cutting-edge part of the base rake-face,
• the diamond-coated rotary cutting tool is provided with a tool rake-face formed by a surface of the rake-face side diamond coating or a surface of the tool rake-face and a following end surface of the flank-face side diamond coating;
• a tool flank-face formed by the surface of the flank-face side diamond coating;
• and a tool cutting-edge part formed at a ridge where the tool rake-face and the tool flank-face crosses, and
• in a perpendicular cross section of the base cutting-edge part, where a straight line connecting a tool-rotation axis and the base cutting-edge part is a base line, a boundary part between the first diamond layer and the second diamond layer at the end surface of the flank-face side diamond coating is exposed at a side nearer to the base flank-face than an extended line of the base line.