a metalcutting tool used to form a thread on a part. Threading tools include thread cutters, taps, threading dies, threading heads, thread-milling cutters, and thread-cutting abrasive disks. Thread cutters—straight-shank, prismatic, and round (disk)—are used to cut external and internal threads in one or several passes, depending on the technique selected. Rotating cutters (prismatic and round multithread) are used for high-speed cutting. Taps are usually used to cut internal threads up to 50 mm in diameter; the taps may be hand taps, nut taps, machine-hand taps, threading-die taps, or sectional master taps. External thread for fasteners—mainly bolts and screws—is produced by means of round and adjustable threading dies.
Threading heads are the most advanced and highly productive tools for machine threading in a single pass. Thread-milling cutters (disk-shaped and hobs) are used to cut external and internal threads. Disk milling cutters are most frequently used for cutting long, multiple threads with a coarse pitch; hobs (multithread) of the arbor and end types are used for cutting short external threads with a moderate pitch (0.5–6 mm). End-type cutters are also used to produce internal threads 15 mm and greater in diameter. Thread-cutting abrasive disks (single-thread and multithread) are used for thread-finishing operations and in thread-grinding machines. The working surfaces of the disk correspond to the thread profile; the surface profile is maintained during cutting by adjustment.
REFERENCEChetverikov, S. S. Metallorezhushchie instrumenty, 5th ed. Moscow, 1965.
A. A. SHISHKIN