An insert portion (3) of a thread mill (1A) is fixed to a leading end portion of a body (2A) using screws (8). The insert portion (3) is configured by overlaying an insert (4) for finish machining and an insert (5) for rough machining. On respective mating faces of the inserts (4, 5), convex portions and concave portions of the mating face of the insert (4) are overlaid with concave portions and convex portions of the mating face of the insert (5). The thread mill (1A) can cut a female screw in a hole formed in a workpiece by performing right-hand cut down-cut milling, for example. The inserts (4, 5) simultaneously cut an inner peripheral surface of the hole, and the rough machining and the finish machining can thus be performed in a single pass. By the convex portions and the concave portions of the respective mating faces of the inserts (4, 5) being overlaid with each other, the inserts (4, 5) partially overlap in their respective thickness directions. As a result, a protrusion length of the insert portion (3) can be shortened.

The milling cutter according to the present invention consists of insert holders (2) where these insert holders (2) project from a carrier disc (1) which is adapted for clamping onto the spindle of a machine tool, and the individual holders (2) are connected with one another by braces (3). Arms (5) are provided between the holders (2) and the carrier disc (1).

A cutting tool for use in an orbital drilling machine may include a cutting-tool body having a longitudinal axis and a plurality of cutting edges supported on the cutting-tool body and distributed circumferentially around the cutting-tool body. Each cutting edge may extend along the longitudinal axis in a respective helix. A circumferential spacing may be defined between each pair of circumferentially adjacent cutting edges for each position of the longitudinal axis along which the cutting edges extend. The circumferential spacing between at least first and second cutting edges of the plurality of cutting edges may be different at spaced-apart first and second positions along the longitudinal axis.

An insert portion (3) of a thread mill (1A) is fixed to a leading end portion of a body (2A) using screws (8). The insert portion (3) is configured by overlaying an insert (4) for finish machining and an insert (5) for rough machining. On respective mating faces of the inserts (4, 5), convex portions and concave portions of the mating face of the insert (4) are overlaid with concave portions and convex portions of the mating face of the insert (5). The thread mill (1A) can cut a female screw in a hole formed in a workpiece by performing right-hand cut down-cut milling, for example. The inserts (4, 5) simultaneously cut an inner peripheral surface of the hole, and the rough machining and the finish machining can thus be performed in a single pass. By the convex portions and the concave portions of the respective mating faces of the inserts (4, 5) being overlaid with each other, the inserts (4, 5) partially overlap in their respective thickness directions. As a result, a protrusion length of the insert portion (3) can be shortened.

An example milling bit comprises a shank and a working sector comprising a cutting anterior part, which is a portion of a hollow sphere, a cutting posterior part fixed to the shank and located between the shank and the spherical anterior part, at least one cutting tooth extending along an entire length of the working sector with a cutting edge, and at least one flute to the cutting tooth extending along length of the working sector following the path of the cutting edge. The spherical anterior part of the working sector is hollow and at least one cutting tooth in the anterior cavity region has a shape of a spherical shell element.

An example milling bit comprises a shank and a working sector comprising a cutting anterior part, which is a portion of a hollow sphere, a cutting posterior part fixed to the shank and located between the shank and the spherical anterior part, at least one cutting tooth extending along an entire length of the working sector with a cutting edge, and at least one flute to the cutting tooth extending along length of the working sector following the path of the cutting edge. The spherical anterior part of the working sector is hollow and at least one cutting tooth in the anterior cavity region has a shape of a spherical shell element.