Principle And Characteristics Of Turning

Turning is a cutting process in which the workpiece rotates while the cutting tool moves in a linear or curved path. A lathe is used to machine parts by performing turning operations on external and internal cylindrical surfaces, end faces, tapered surfaces, formed surfaces, threads, and more.

 

When turning external or internal cylindrical surfaces, the tool moves parallel to the rotational axis of the workpiece. For facing or cutting off the workpiece, the tool moves horizontally perpendicular to the rotational axis. Conical surfaces are produced when the tool's path is at an angle to the workpiece axis. Formed surfaces of revolution can be machined using form tools or by controlling the tool's trajectory.

 

During cutting, the workpiece rotates as the primary motion, driven by the machine spindle, while the lathe tool, held in the tool post, performs the feed motion. Cutting speed (v) refers to the linear speed (in meters per minute) at the contact point between the rotating workpiece surface and the tool. Depth of cut refers to the perpendicular distance (in millimeters) between the machined surface and the surface to be machined in each pass, though in cutoff and form turning, it is measured as the contact length perpendicular to the workpiece. Feed refers to the displacement of the tool along the feed direction per revolution of the workpiece (mm/rev) and can also be expressed as the feed per minute (mm/min).

 

When turning mild steel with high-speed steel tools, cutting speeds typically range from 25 to 60 meters per minute, while carbide tools can achieve 80 to 200 meters per minute. Coated carbide tools can reach speeds exceeding 300 meters per minute.