A front and back chamfering rotary milling cutter includes a cutter body including an insert pocket and a star-shaped indexable cutting insert releasably retained in the pocket. The cutting insert has star-shaped upper and lower surfaces connected by a peripheral surface intersecting each of the upper and lower surfaces. The cutting insert includes a plurality of circumferentially alternating inner and outer corner portions. A cutting portion is defined by each outer corner portion together with an adjacent first inner corner portion rotationally forward thereof and an adjacent second inner corner portion located rotationally rearward thereof. Each cutting portion includes a front chamfering cutting edge extending from the outer corner portion to the first inner corner portion and a back chamfering cutting edge extending from the outer corner portion to the second inner corner portion.

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 front and back chamfering rotary milling cutter includes a cutter body including an insert pocket and a star-shaped indexable cutting insert releasably retained in the pocket. The cutting insert has star-shaped upper and lower surfaces connected by a peripheral surface intersecting each of the upper and lower surfaces. The cutting insert includes a plurality of circumferentially alternating inner and outer corner portions. A cutting portion is defined by each outer corner portion together with an adjacent first inner corner portion rotationally forward thereof and an adjacent second inner corner portion located rotationally rearward thereof. Each cutting portion includes a front chamfering cutting edge extending from the outer corner portion to the first inner corner portion and a back chamfering cutting edge extending from the outer corner portion to the second inner corner portion.