Provided is a cutting insert configured to be able to realize downsizing of a cutting tool. A cutting insert includes: an upper surface and a lower surface facing each other and having a plurality of corner parts; a side surface connecting the upper surface and the lower surface and forming intersecting edges with the upper surface and the lower surface, respectively; and a through hole that has a central axis extending from the upper surface to the lower surface and that is formed for penetration from the upper surface to the lower surface. A corner cutting edge arranged at a position corresponding to a corner part of the upper surface, a minor cutting edge connected to a first end of the corner cutting edge, and a major cutting edge connected to a second end of the corner cutting edge are formed on the intersecting edge between the upper surface and the side surface. A flank of the corner cutting edge and a recessed part located on the lower surface side of the flank of the corner cutting edge are formed on the side surface.

A rotary cutting blade material has an attaching structure forming portion that is to serve as an attaching portion to the shank, a cutting structure forming portion that is to serve as a cutting blade, and a joint portion. The cutting structure forming portion has a core portion and a surface portion provided on the attaching structure forming portion with the joint portion being interposed, and the surface portion covers at least a part of a surface of the core portion. The attaching structure forming portion includes a hard material including a hard component and one or two or more types of iron group elements, and the hard material has a Young's modulus of not more than 350 GPa. The core portion includes a cemented carbide material, and the surface portion includes PCD or CBN.

A rotary cutting tool includes a shaft having and outer surface and having a longitudinal axis, a plurality of helical flutes formed in the shaft about the longitudinal axis, a plurality of helical cutting edges formed at an interface with the outer surface and a respective helical flute about the longitudinal axis, and a plurality of end cutting edges located on an axial distal end of a cutting portion of the shaft, the end cutting edges being contiguous with a corresponding one of the plurality of helical cutting edges and forming a corner in the transition between each of the end cutting edges and the corresponding one of the plurality of helical cutting edges. A hone edge extends along a portion of each of the end cutting edges, the associated corner and a portion of the corresponding one of the plurality of helical cutting edges.

Rotary cutting tool (100) having plurality of major flutes (130) arranged helically opposite to plurality of discontinuous minor flutes (135) and intersecting to form plurality of teeth. Each tooth includes a first cutting edge formed with the major flute and a second cutting edge formed with the minor flute, the first and second cutting edges meeting at an apex and form part of a periphery of a quadrilateral-shaped face portion. The face portion has non-planar surfaces extending from the respective first and second cutting edges that define a relief surface of each cutting edge. First and second cutting edges are arranged on an imaginary cylinder having a center axis coaxial with the axis of rotation of the tool and respective relief surfaces are radially inward of a surface of the imaginary cylinder such that the first and second cutting edges each have a clearance in a rotational direction of the tool.