The throwaway insert includes a base and a cutting edge member. The cutting edge member includes a rake face, a flank face, a first connecting face, a second connecting face, and a first ridgeline serving as a cutting edge. The rake face includes a main surface and a first chamfer provided at an edge tip portion of the cutting edge member, the edge tip portion including an extreme tip portion of the cutting edge member. In a plan view from an upper surface of the base, the flank face, the first connecting face, and the second connecting face are located external to the base. The first chamfer is inclined relative to the main surface so as to increase a thickness of the cutting edge member as the first chamfer is closer to the main surface.

A turning tool includes: a holder portion; and a cutting edge portion fixed to the holder portion, wherein the cutting edge portion is composed of a synthetic single-crystal diamond, and the cutting edge portion has a nose curvature having a curvature radius of more than or equal to 0.1 mm and less than or equal to 1.2 mm, and the nose curvature satisfies at least one of a condition that a direction of a line of intersection between the rake face and a bisecting cross section of a vertex angle of the nose curvature is within ?10? relative to a <110> direction of the synthetic single-crystal diamond, and a condition that the direction of the line of intersection between the rake face and the bisecting cross section of the vertex angle of the nose curvature is within ?10? relative to a <100> direction of the synthetic single-crystal diamond.

A cutting tool including a substrate and a coating film disposed on the substrate, wherein the cutting tool includes: a rake face, a flank face contiguous to the rake face; and a cutting edge region composed of a boundary part between the rake face and the flank face, wherein the coating film includes a TiSiCN layer, the TiSiCN layer has: a first TiSiCN layer positioned in the rake face; and a second TiSiCN layer positioned in the cutting edge region, the first TiSiCN layer has a composition of Ti.sub.(1-Xr)Si.sub.XrCN, the second TiSiCN layer has a composition of Ti.sub.(1-Xe)Si.sub.XeCN, and the Xr and the Xe each represent 0.010 or more and 0.100 or less, and satisfy a relationship of Xr?Xe?0.003.

Provided is a cutting tool that simultaneously improves both fracture resistance and wear resistance. The cutting tool according to the present invention has an end surface, a peripheral side surface intersecting with the end surface, and a cutting edge in an intersecting ridge part along the end surface and the peripheral side surface, and when first and second points A and B are defined on the cutting edge, the first point A protrudes further toward an outer side of the cutting tool than the second point B. The cutting edge has a honing surface. The honing surface has a portion, the width of which gradually increases from the first point A toward the second point B.

A cutting tool including a substrate and a coating film disposed on the substrate, wherein the cutting tool includes: a rake face, a flank face contiguous to the rake face; and a cutting edge region composed of a boundary part between the rake face and the flank face, wherein the coating film includes a TiSiCN layer, the TiSiCN layer has: a first TiSiCN layer positioned in the rake face; and a second TiSiCN layer positioned in the cutting edge region, the first TiSiCN layer has a composition of Ti.sub.(1-Xr)Si.sub.XrCN, the second TiSiCN layer has a composition of Ti.sub.(1-Xe)Si.sub.XeCN, and the Xr and the Xe each represent 0.010 or more and 0.100 or less, and satisfy a relationship of Xr?Xe?0.003.

A cutting tool according to an aspect of the present invention is a cutting tool for cutting a rotationally symmetrical surface of a rotating workpiece. The cutting includes the step of feeding the cutting tool in a direction inclined with respect to a rotational axis of the rotationally symmetrical surface, while holding the cutting tool in contact with the rotationally symmetrical surface. In the step of feeding the cutting tool, the cutting tool has a point that is in contact with the rotationally symmetrical surface and the point shifts as the cutting tool is fed. The cutting tool includes: a rake face; a flank face; and a cutting edge connecting the rake face and the flank face. The cutting edge as seen from above the flank face has a shape including at least one arc, and the arc has a radius of curvature of not less than 100 mm and not more than 500 mm.

The invention relates to a cutting insert (1) for installation in carrier tools for machining workpieces, comprising a top side (2), a bottom side (3), and side surfaces (4) connecting the top side (2) and the bottom side (3), wherein a peripheral protective chamfer (5) having an upper edge (6) adjoining the top side (2) of the cutting insert (1) and having a lower edge (7) adjoining the side surfaces (4) is arranged at the transition from the top side (2) to the side surfaces (4), wherein the upper edge (6) forms cutting edges (9) and cutting corners (10) and, in the region of the cutting edges (9), the lower edge (7) transitions into a cutting-edge clearance angle surface (8) having an edge clearance angle of 3 to 11. For improved edge stability in drawn cuts, it is proposed that, in the region of the cutting corners (10), the lower edge (7) of the protective chamfer (5) transitions into a corner clearance angle surface (11) having an edge clearance angle of 3 to 5.

A cutting insert including a surface involved in cutting, for which a cutting tool material of a hard sintered body is used. A radius of a nose R portion is 0.4 mm or greater and 2.4 mm or less, an apex angle of the nose R portion is 50 or greater and 95 or less, a rake angle at a position of a bisecting plane of the apex angle of the nose R portion is 1 or greater and 10 or less, a chamfer provided in a cutting edge portion is a negative land with unequal width, and at least on one side of the negative land with respect to a boundary which is an apex of a nose R portion cutting edge, a width of the negative land gradually decreases from the apex of the nose R portion cutting edge to a position at which the nose R portion cutting edge is connected to a linear cutting edge. Let W1 be the width of the negative land at the apex of the nose R portion cutting edge, and W2 be the width of the negative land at both ends of the nose R portion cutting edge, then the W1 is 0.04 mm or greater and 0.2 mm or less, and a ratio of the W1 to the W2 is 1.5 or greater.

A cutting tool which allows for fracture resistance and cutting resistance to be improved at the same time is provided. A cutting tool according to the present invention is a cutting tool 1 comprising an end surface 10, first and second side surfaces 13, 14 which intersect with the end surface 10, a first cutting edge 20a in an intersecting edge between the end surface 10 and the first side surface 13, and a second cutting edge 20b in an intersecting edge between the end surface 10 and the second side surface 14, wherein: the first cutting edge 20a has a first honing surface 21a; and the second cutting edge 20b has a second honing surface 21b. A cross-sectional shape of the second honing surface 21b is different from a cross-sectional shape of the first honing surface 21a.

Provided is a cutting tool that simultaneously improves both fracture resistance and wear resistance. The cutting tool according to the present invention has an end surface, a peripheral side surface intersecting with the end surface, and a cutting edge in an intersecting ridge part along the end surface and the peripheral side surface, and when first and second points A and B are defined on the cutting edge, the first point A protrudes further toward an outer side of the cutting tool than the second point B. The cutting edge has a honing surface. The honing surface has a portion, the width of which gradually increases from the first point A toward the second point B.