a metalcutting machine designed to cut external and internal thread by means of a thread cutter. The blank and thread cutter perform several motions as the thread is formed on a thread-milling machine. The thread cutter rotates about its axis (principal motion); the blank slowly rotates (circular feed); the blank or thread cutter moves longitudinally (traverse feed, which is equal to the pitch of the thread being cut per rotation of the blank); and the thread cutter penetrates to the depth of the thread (radial feed).
Semiautomatic and automatic thread-milling machines cut external and internal threads with a coarse screw pitch over a considerable distance by means of face and side cutters. They are also used to cut threads with a fine screw pitch over a short distance by means of hobbing cutters, the screw pitch equaling the pitch of the thread being cut during 1.25–1.5 rotations of the blank.