Abstract: In an otherwise conventional, mechanically controlled lathe the workpiece support spindle can be disconnected from the main mechanical drive transmission and coupled to the main drive motor via a second mechanical transmission which can introduce an angular offset between the workpiece support spindle and a milling tool that is proportional to the travel along the feed axis of a toolholder carriage carrying the milling tool. The angular offset is introduced by a coupling sleeve coupling two transmission half-shafts via helical teeth to transmit movement to the workpiece support spindle. The coupling sleeve is moved axially by the toolholder carriage. In this way straight threads and helical threads with a large pitch can be cut on an otherwise conventional lathe.

Abstract: In accordance with the invention, the workpiece (1) is mounted on a lathe headstock spindle rotated by drive means about a headstock spindle axis (I--I). A turning tool (3) is mounted on a toolholder carriage adapted to move in translation along an infeed axis (III) and along a carriage axis (IV). The turning tool (3) has a cutting edge (4) made up of a plurality of cutting edge portions adapted to be individually engaged with the workpiece (1). The turning tool (3) is rotated about an axis (II) which is not parallel to the headstock spindle axis (I--I) to bring the separate portions of the cutting edge (4) of the turning tool (3) successively into contact with the workpiece (1). The invention can be used to cut helical threads.