A rotary cutting tool includes a tool body and a cutting edge tip provided at the tool body. At least one first groove is provided in a rake face of the cutting edge tip, the first groove has a portion inclined with respect to a rotation axis, and a front end of the first groove is provided at a front cutting edge. A rear end of the first groove is provided on an inner side with respect to an outer peripheral cutting edge, and an irregularity of the outer peripheral cutting edge is 30 μm or less.

A rotary cutting tool includes a tool body and a cutting edge tip provided at the tool body. At least one first groove is provided in a rake face of the cutting edge tip, the first groove has a portion inclined with respect to a rotation axis, and a front end of the first groove is provided at a front cutting edge. A rear end of the first groove is provided on an inner side with respect to an outer peripheral cutting edge, and an irregularity of the outer peripheral cutting edge is 30 μm or less.

A cutting tool may include a base member and a diamond layer located on the base member. The cutting tool may include a first surface, a second surface, and a cutting edge located in at least a part of a ridge line which the first surface intersects with the second surface. The diamond layer may be located in at least a part of the first surface, at least a part of the second surface, and at least a part of the cutting edge. A maximum height in the cutting edge may be smaller than a maximum height in the first surface. The maximum height in the cutting edge may be greater than a maximum height in the second surface.

An ultra-fine nanocrystalline diamond precision cutting tool and a manufacturing method therefor. A diamond cutter is made of a thick self-supporting film of ultra-fine nanocrystalline diamond, the thick film having a thickness of 100-3000 microns, where 1 nanometer≤diamond grain size≤20 nanometers. In the manufacturing method, the growth of ultra-fine nanocrystalline diamond on a silicon substrate is accomplished by means of two steps of direct current hot cathode glow discharge chemical vapor deposition and hot filament chemical vapor deposition, then the silicon substrate is separated from the diamond to obtain a thick self-supporting film of ultra-fine nanocrystalline diamond, the thick self-supporting film of ultra-fine nanocrystalline diamond is laser cut and then welded to a cutter body, and then by means of edging, rough grinding and fine grinding, an ultra-fine nanocrystalline diamond precision cutting tool is obtained.

An ultra-fine nanocrystalline diamond precision cutting tool and a manufacturing method therefor. A diamond cutter is made of a thick self-supporting film of ultra-fine nanocrystalline diamond, the thick film having a thickness of 100-3000 microns, where 1 nanometer≤diamond grain size≤20 nanometers. In the manufacturing method, the growth of ultra-fine nanocrystalline diamond on a silicon substrate is accomplished by means of two steps of direct current hot cathode glow discharge chemical vapor deposition and hot filament chemical vapor deposition, then the silicon substrate is separated from the diamond to obtain a thick self-supporting film of ultra-fine nanocrystalline diamond, the thick self-supporting film of ultra-fine nanocrystalline diamond is laser cut and then welded to a cutter body, and then by means of edging, rough grinding and fine grinding, an ultra-fine nanocrystalline diamond precision cutting tool is obtained.

A cBN sintered body has 40%-85% cBN by volume and 15% to 60% binder phase by volume. and inevitable impurities. The binder phase has an Al compound including Al and at least one element selected from N, O and B, and a Zr compound including Zr and at least one element selected from C, N, O and B. The Zr compound includes ZrO, or ZrO and ZrO.sub.2. In an X-ray diffraction, where a peak intensity of a (111) plane of the ZrO is I.sub.1, a peak intensity of a (101) plane of tetragonal ZrO.sub.2 is I.sub.2t and a peak intensity of a (111) plane of cubic ZrO.sub.2 is I.sub.2c, a ratio of the intensity of I.sub.1 to total intensities of I.sub.1, I.sub.2t and I.sub.2c is 0.6-1.0, and an average grain size of the Al compound is 80 nm-300 nm.

A cutting tool includes: a base metal provided with a seat portion; a blade edge member that is a polycrystalline diamond sintered material containing polycrystalline diamond and a binder; and a brazing material that fixes the blade edge member to the seat portion of the base metal. The blade edge member has a thickness of greater than or equal to 0.3 mm. The brazing material is disposed between a blade edge bottom face of the blade edge member and the a seat bottom face of the seat portion and is in contact with the blade edge bottom face and the seat bottom face. The flank face is located outside of the base metal with respect to the lateral face of the base metal.

A cutting tool includes: a base metal provided with a seat portion; a blade edge member that is a polycrystalline diamond sintered material containing polycrystalline diamond and a binder; and a brazing material that fixes the blade edge member to the seat portion of the base metal. The blade edge member has a thickness of greater than or equal to 0.3 mm. The brazing material is disposed between a blade edge bottom face of the blade edge member and the a seat bottom face of the seat portion and is in contact with the blade edge bottom face and the seat bottom face. The flank face is located outside of the base metal with respect to the lateral face of the base metal.

A composite sintered material includes a plurality of diamond grains, a plurality of cubic boron nitride grains, and a remainder of a binder phase, wherein the binder phase includes cobalt, a content of the cubic boron nitride grains in the composite sintered material is more than or equal to 3 volume % and less than or equal to 40 volume %, and an average length of line segments extending across continuous cubic boron nitride grains in appropriately specified straight lines extending through the composite sintered material is less than or equal to a length three times as large as an average grain size of the cubic boron nitride grains.

A cutting tool rotates about a rotation axis, and includes a tip end portion. The tip end portion includes a partially spherical surface that is brought into contact with a workpiece. The surface is provided with a plurality of recesses disposed apart from each other. An opening edge of each of the plurality of recesses constitutes a cutting edge.