Abstract: The boundary flow path is constituted of a pair of boundary wall surfaces facing each other in a first cross section intersecting each of the first flow path, the boundary flow path, and the second flow path. An inclination of a tangent to at least one of the pair of boundary wall surfaces is continuously changed. In a second cross section perpendicular to a direction in which coolant flows, a lateral width of the first flow path is larger than a longitudinal width of the first flow path and a lateral width of the second flow path is larger than a longitudinal width of the second flow path when a longitudinal direction represents a direction in which the pair of boundary wall surfaces face each other and a lateral direction represents a direction perpendicular to the longitudinal direction.

Abstract: One object of the present invention is to increase stability for fixing a cutting tool with a holder formed of a sleeve, and to improve machining accuracy of a boring tool using the holder and prevent chipping of a cutting edge. In a holder for a boring tool holding a bar-shaped cutting tool by receiving it in a center hole in a sleeve and clamping it with clamp means, the sleeve is provided with a slit cutting a region from the center hole in the sleeve to an outer periphery surface thereof lengthwise from a front end to a longitudinal partway portion of the sleeve, and is further provided with a fastener tightening a slit-formed portion of the sleeve to change an inner diameter of the center hole.

Abstract: A superhard sintered body containing cubic boron nitride is bonded to an apical angle part of a tool body having a polygonal shape, and an edge and a chip breaker are formed on the superhard sintered body. A chamfer is formed on the intersection between the upper surface and the side surface of the superhard sintered body, the chip breaker has a protrusion, and an angle ? formed by ridges on the apex of the protrusion or a tangential line at a point bisecting the ridges and a bisector for the apical angle and the ratio of the distance between a first intersection between the two ridges on the apex of the protrusion and an extreme point of the first ridge to the distance between a second intersection between a straight line passing through the first intersection and the extreme point and the outer periphery of the tool body and the first intersection are in prescribed ranges.

Abstract: A superhard sintered body containing cubic boron nitride is bonded to an apical angle part of a tool body having a polygonal shape, and an edge and a chip breaker are formed on the superhard sintered body. A chamfer is formed on the intersection between the upper surface and the side surface of the superhard sintered body, the chip breaker has a protrusion, and an angle ? formed by ridges on the apex of the protrusion or a tangential line at a point bisecting the ridges and a bisector for the apical angle and the ratio of the distance between a first intersection between the two ridges on the apex of the protrusion and an extreme point of the first ridge to the distance between a second intersection between a straight line passing through the first intersection and the extreme point and the outer periphery of the tool body and the first intersection are in prescribed ranges.