Screwcutting

Screwcutting is the machining of screw threads on cylindrical workpieces by removing material with a single‑point cutting tool, usually on a lathe or on a compatible machine. It creates helical threads that can be external (on bolts or studs) or internal (in tapped holes). In traditional manual screwcutting, the lathe’s leadscrew and gear train drive the tool’s axial movement so that the tool advances a pitch distance for every spindle turn, forming the thread profile.

The primary method is single‑point threading on a lathe. The operator selects a thread form and pitch (for example metric, Unified, or Whitworth), mounts a suitable threading tool, and uses the carriage and sometimes the tailstock for support. The tool is fed toward the work at a rate that matches the chosen pitch, producing one complete turn of thread per revolution. After rough passes, finishing passes improve thread quality. Internal threads are produced by tapping or by a corresponding internal threading tool; external threads are formed with a turning tool or by a die in other setups. Modern practice often uses CNC lathes that interpolate the thread path automatically.

Setup and quality control are crucial: correct tool geometry, appropriate depth of cut, proper chamfering at the start of the thread, and measurement with thread gauges or a calliper to verify pitch and diameter. Screwcutting standards across systems include metric ISO, UN/UNF, and Whitworth thread forms. Applications span fasteners, threaded adaptors, shafts, and any component requiring mating threads.