A cutting tool comprises a shank having an insertion portion protruding from a shank main body, a head in which an insertion hole into which the insertion portion is inserted is formed, and a spacer disposed in a gap between the shank main body and the head. The insertion portion has a tapered outer circumferential surface which gradually decreases in diameter from the other side toward one side in the axial direction. The insertion hole has a tapered inner circumferential surface coming into surface contact with the tapered outer circumferential surface. A head end surface of the head which faces the other side in the axial direction comes into surface contact with a surface facing one side in the axial direction of the spacer.

A cutting insert has opposing upper and lower surfaces interconnected by a peripheral side surface, an insert axis passing through the upper and lower surfaces, and first and second upper cutting edges formed at the intersection of the upper surface and the peripheral side surface. A lower central protuberance having first, second, third and fourth abutment walls extends downwardly from the lower surface. In a cross-section taken in a first horizontal plane perpendicular to the insert axis and intersecting the lower central protuberance, the first, second, third and fourth abutment walls define an imaginary quadrilateral having diagonally opposing first and third internal angles and diagonally opposing second and fourth internal angles. The first and third internal angles are equal to each other, and the second and fourth internal angles are not equal to each other. Two cutting inserts are removably secured in a rotary cutting tool.

A cutting insert has opposing upper and lower surfaces interconnected by a peripheral side surface, an insert axis passing through the upper and lower surfaces, and first and second upper cutting edges formed at the intersection of the upper surface and the peripheral side surface. A lower central protuberance having first, second, third and fourth abutment walls extends downwardly from the lower surface. In a cross-section taken in a first horizontal plane perpendicular to the insert axis and intersecting the lower central protuberance, the first, second, third and fourth abutment walls define an imaginary quadrilateral having diagonally opposing first and third internal angles and diagonally opposing second and fourth internal angles. The first and third internal angles are equal to each other, and the second and fourth internal angles are not equal to each other. Two cutting inserts are removably secured in a rotary cutting tool.

A cutting insert includes a rake face, a seating face facing an opposite side to the rake face and seated on an insert mounting seat, and a flank face extending around the rake face and the seating face, in which two cutting edges each having an arcuate cutting edge portion extending in an arc shape and a linear cutting edge portion which is in contact with the arcuate cutting edge portion are formed on an intersecting ridgeline portion between the rake face and the flank face, a groove portion having a wall surface coming into contact with a projection portion protruding from a bottom surface of the insert mounting seat is formed on the seating face, and the groove portion has a narrow width portion in which a groove width decreases from one end side toward the other end side in a direction in which the groove portion extends.

A cutting insert includes a rake face, a seating face facing an opposite side to the rake face and seated on an insert mounting seat, and a flank face extending around the rake face and the seating face, in which two cutting edges each having an arcuate cutting edge portion extending in an arc shape and a linear cutting edge portion which is in contact with the arcuate cutting edge portion are formed on an intersecting ridgeline portion between the rake face and the flank face, a groove portion having a wall surface coming into contact with a projection portion protruding from a bottom surface of the insert mounting seat is formed on the seating face, and the groove portion has a narrow width portion in which a groove width decreases from one end side toward the other end side in a direction in which the groove portion extends.

In this cutting insert, two cutting edges respectively including arc-shaped cutting edge parts extending in an arc shape in a plan view and linear cutting edge parts are provided in an intersection ridge line part between a rake face and a flank face. The cutting edges include a convex curved part moving away from a seating face and then moving close to the seating face as at least the arc-shaped cutting edge part moves away from the linear cutting edge parts. In a side view, the arc-shaped cutting edge parts include curvature change points between most protruding points farthest from the seating face and cutting edge tips of the arc-shaped cutting edge parts.

A cutting tool comprises a shank having an insertion portion protruding from a shank main body, a head in which an insertion hole into which the insertion portion is inserted is formed, and a spacer disposed in a gap between the shank main body and the head. The insertion portion has a tapered outer circumferential surface which gradually decreases in diameter from the other side toward one side in the axial direction. The insertion hole has a tapered inner circumferential surface coming into surface contact with the tapered outer circumferential surface. A head end surface of the head which faces the other side in the axial direction comes into surface contact with a surface facing one side in the axial direction of the spacer.

A cutting insert has top and bottom surfaces opposing each other and a side surface connecting them. A part of an intersecting ridge between the top and side surfaces functions as a cutting edge. On the side surface, a side surface portion adjacent to the intersecting ridge portion opposing the cutting edge intersects the top surface at an acute angle. At least on a part of a bottom surface, an inclined surface gradually approaching the top surface with increasing distance from a side surface portion on a side opposite to a cutting edge is formed. This allows a part of the cutting resistance to act on the side surface portion. As a result, friction resistance between the side surface portion and the side surface of an insert seat becomes larger, thereby suppressing a shifting of the cutting insert when cutting.

A ballnose cutting insert has a top face, a bottom face, a plurality of side clearance faces, a first nose corner, a second nose corner, and a first elongate cutting edge at the top face, a second elongate cutting edge at the top face, and a fastener bore with a center. There is a first open-end notch below the first nose corner, and a second open-end notch below the second nose corner. The first open-end notch is defined at least in part by a first generally planar engaging surface, and the second open-end notch is defined at least in part by a second generally planar engaging surface. The first generally planar engaging surface is disposed at a disposition angle relative to the second engaging surface, and the disposition angle is not equal to zero degrees. The first generally planar engaging surface is disposed from the center of the fastener bore a first abutment distance as measured along a line perpendicular to the first generally planar engaging surface. The second generally planar engaging surface is disposed from the center of the fastener bore a second abutment distance as measured along a line perpendicular to the second generally planar engaging surface. The first abutment distance is equal to the second abutment distance.

A double-sided ball end mill includes a body having a generally hemispherical forward end portion and a rearward end portion. The forward end portion includes insert-receiving pockets and chip pockets. A cutting insert can be mounted within each insert-receiving pocket. The cutting insert includes a first substantially planar surface, a second substantially planar surface, a first curvilinear side surface, a second curvilinear side surface, a first pair of cutting edges formed at an intersection between the first substantially planar surface and the first and second curvilinear side surfaces, and a second pair of cutting edges formed at an intersection between the second substantially planar surface and the first and second curvilinear side surfaces. The first and second planar surfaces are substantially parallel to each other, and the cutting insert is mirror symmetric about all three axes.