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.

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.

A round cutting insert for a milling tool having a center axis and a neutral plane extending perpendicularly thereto. The round cutting insert includes a circumferential side surface surrounding the center axis between upper and lower round main surfaces. An upper cutting edge is formed along the intersection of the upper round main surface and the side surface. A plurality of elongated support grooves are arranged in the side surface. Each elongated support groove has a bottom surface extending in a lengthwise direction with opposite flank surfaces converging toward the bottom surface and extending in parallel with the lengthwise direction of the elongated support groove. The lengthwise direction of each elongated support groove forms an acute angle with the neutral plane as seen in a side view. At least one of the opposite flank surfaces of each elongated support groove is configured as a side support surface.

A cutting insert including a first end surface, a second end surface and a peripheral side surface extending therebetween. The first and second end surfaces each having one substantially quadrangular portion and two substantially semicircular portions which are respectively joined to two opposing sides of the substantially quadrangular portion. An intersecting edge between each of the first and second end surfaces and the peripheral side surface is provided with a cutting edge. The cutting edge is formed in at least part of the substantially semicircular portion. At least part of a portion of the peripheral side surface which is adjacent to the substantially quadrangular portion of each of the first and second end surfaces, and at least part of a portion of the peripheral side surface which is adjacent to the substantially semicircular portion, each have a function of coming into contact with an insert seat.

A tool body of a cutting tool includes at least one insert pocket having a bottom surface with a support face configured to provide support to a lower surface of an insert to be received in the pocket and having at least one cutting edge formed between a top surface and a side surface connecting the lower surface and the top surface. The bottom surface of the pocket has a countersunk central portion surrounded by a peripheral bottom surface portion configured to form the only support face of the bottom surface to the lower surface of an insert to be received in the pocket.

A cutting insert including a first end surface, a second end surface and a peripheral side surface extending therebetween. The first and second end surfaces each having one substantially quadrangular portion and two substantially semicircular portions which are respectively joined to two opposing sides of the substantially quadrangular portion. An intersecting edge between each of the first and second end surfaces and the peripheral side surface is provided with a cutting edge. The cutting edge is formed in at least part of the substantially semicircular portion. At least part of a portion of the peripheral side surface which is adjacent to the substantially quadrangular portion of each of the first and second end surfaces, and at least part of a portion of the peripheral side surface which is adjacent to the substantially semicircular portion, each have a function of coming into contact with an insert seat.