In a cutting tool having an indexable lay-down cutting insert with a central body portion and three circumferentially spaced apart cutting portions, the cutting insert is removably secured to an elongated holding portion of an insert holder. Each cutting portion has a cutting edge with first and second cutting end points, the cutting edge formed at the intersection of an upward facing rake surface and a radially outward facing relief surface. In a top view of the cutting insert, parallel imaginary first and second vertical planes containing the first and second cutting end points, intersect the central body portion at first and second body side points, which are located first and second cutting distances from the first and second cutting end points, respectively. Each of the first and second cutting distances is greater than twenty-five percent of the first radius of an imaginary first circle circumscribing the cutting insert.

A cutting tool including a toolholder and a round cutting insert for mounting on a pocket floor of the toolholder. The toolholder includes the toolholder pocket floor having a bore therein and a plurality of grooves in the pocket floor arranged radially about the bore, wherein adjacent grooves are radially offset by a groove offset angle x. The round cutting insert includes an upper surface having a cutting edge, a lower surface opposite the upper surface, an exterior side surface between the upper surface and the lower surface, an interior side surface defining an aperture extending from the upper surface to the lower surface, and a plurality of lugs arranged radially about the aperture, wherein adjacent lugs are radially offset by a lug offset angle y, and wherein a ratio of y:x is an integer greater than or equal to 2.

A cutting tool body for indexable inserts, and a round milling insert, are configured not to cause floating or rattling upon mounting the milling insert. The tool body includes a recessed portion for fitting one of a plurality of protrusions thereto, the protrusions being formed in the milling insert to protrude in the radial direction. The recessed portion has two inner surfaces having curved portions disposed so the distance between them gradually decreases at the contact area between the recessed portion and the protrusion fitted thereto. The milling insert includes protrusions protruding radially, any of which fit into a recessed portion on a mounting seat of the tool body. The protrusions each have two curved outer surfaces arranged so the distance between them gradually decreases toward a tip of the protrusion, at the contact area between the protrusion and the recessed portion into which the protrusion is fitted.

A cutting tool has a tool body having at least one pocket, at least one cutting insert releasably fixed to the pocket and a fastening device for securing the insert in the pocket. The pocket has a raised portion) with a flat upper support face arranged to be received in a recess of the insert and support the insert by receiving a bottom surface of the recess bearing on the support face. A projecting member of the raised portion has delimiting walls designed to bear against border walls of the recess of an insert for establishing mutual contact therewith and prevent rotation of the insert in the pocket by receiving a rotational moment acting on the insert in an active chip-removing state of the tool.

Provided are a cutting insert and a tool holder on which the cutting insert is provided. The cutting insert includes a circular upper surface, a circular lower surface, a cylindrical lateral surface for connecting the upper surface and the lower surface, an upper cutting edge formed between the upper surface and the lateral surface, a lower cutting edge formed between the lower surface and the lateral surface, and a plurality of rotation-preventing parts provided at the lateral surface so as to prevent the cutting insert from rotating with respect to the tool holder. Each rotation preventing part includes an inner curved surface recessed toward the center of the lateral surface and convexly rounded so as to form concentric circles in conjunction with the lateral surface, and a stepped rotation-preventing surface parallel to the axial direction of the insert and connecting the inner curved surface and the lateral surface.

Chip discharge control is further improved. A cutting insert includes an upper surface, a lower surface, a screw hole having an axis penetrating from the upper surface to the lower surface, a peripheral side surface, and a major cutting edge, a wiper edge, and an inner edge formed in an intersecting region between the upper surface and the peripheral side surface. In a side view in which the peripheral side surface on which the inner edge is formed is seen from a direction perpendicular to the axis, the inner edge includes a recessed part recessed toward the lower surface, a length D.sub.L of the inner edge on one side of the recessed part in the side view is longer than a length D.sub.R of the inner edge on the other side of the recessed part, a lowest point of the inner edge is at a position lower than a flat part of the upper surface, and at least a part of the inner edge on the one side is at a position higher than the flat part of the upper surface. A cutting edge angle φ.sub.23L of the inner edge on the one side of the recessed part is larger than a half of a cutting edge angle φ.sub.23R of the inner edge on the other side of the recessed part.

A cutting tool including a toolholder and a round cutting insert for mounting on a pocket floor of the toolholder. The toolholder includes the toolholder pocket floor having a bore therein and a plurality of grooves in the pocket floor arranged radially about the bore, wherein adjacent grooves are radially offset by a groove offset angle x. The round cutting insert includes an upper surface having a cutting edge, a lower surface opposite the upper surface, an exterior side surface between the upper surface and the lower surface, an interior side surface defining an aperture extending from the upper surface to the lower surface, and a plurality of lugs arranged radially about the aperture, wherein adjacent lugs are radially offset by a lug offset angle y, and wherein a ratio of y:x is an integer greater than or equal to 2.

In a cutting tool having an indexable lay-down cutting insert with a central body portion and three circumferentially spaced apart cutting portions, the cutting insert is removably secured to an elongated holding portion of an insert holder. Each cutting portion has a cutting edge with first and second cutting end points, the cutting edge formed at the intersection of an upward facing rake surface and a radially outward facing relief surface. In a top view of the cutting insert, parallel imaginary first and second vertical planes containing the first and second cutting end points, intersect the central body portion at first and second body side points, which are located first and second cutting distances from the first and second cutting end points, respectively. Each of the first and second cutting distances is greater than twenty-five percent of the first radius of an imaginary first circle circumscribing the cutting insert.

Chip discharge control is further improved. A cutting insert includes an upper surface, a lower surface, a screw hole having an axis penetrating from the upper surface to the lower surface, a peripheral side surface, and a major cutting edge, a wiper edge, and an inner edge formed in an intersecting region between the upper surface and the peripheral side surface. In a side view in which the peripheral side surface on which the inner edge is formed is seen from a direction perpendicular to the axis, the inner edge includes a recessed part recessed toward the lower surface, a length D.sub.L of the inner edge on one side of the recessed part in the side view is longer than a length D.sub.R of the inner edge on the other side of the recessed part, a lowest point of the inner edge is at a position lower than a flat part of the upper surface, and at least a part of the inner edge on the one side is at a position higher than the flat part of the upper surface. A cutting edge angle φ.sub.23L of the inner edge on the one side of the recessed part is larger than a half of a cutting edge angle φ.sub.23R of the inner edge on the other side of the recessed part.

Provided are a tool body of a cutting tool for indexable inserts and a round milling insert that are configured not to cause floating or rattling when the round milling insert is mounted, by keeping the contact part between the round milling insert and the tool body at a predetermined part. The tool body includes a recessed portion provided so that only one of a plurality of protrusions is fitted thereto, the plurality of protrusions being formed in the round milling insert so as to protrude in the radial direction, wherein the recessed portion has both inner surfaces thereof formed of curved surfaces in such a manner that the distance therebetween gradually decreases toward a depth portion, at the contact area between the recessed portion and said protrusion fitted thereto out of the plurality of protrusions. The round milling insert mounted onto such tool body includes a plurality of protrusions formed so as to protrude in the radial direction, any of the plurality of protrusions being able to be fitted into a recessed portion provided on a mounting seat of the tool body, wherein each of the protrusions has both outer surfaces thereof formed of curved surfaces in such a manner that the distance therebetween gradually decreases toward a tip of the protrusion, at the contact area between the protrusion and the recessed portion into which the protrusion is fitted.