How Turning Works

The workpiece rotates, and the turning tool moves in a straight line or a curve in the plane. Turning is generally carried out on a lathe to process the inner and outer cylindrical surfaces, end surfaces, conical surfaces, forming surfaces and threads of the workpiece.
When turning the inner and outer cylindrical surfaces, the turning tool moves in a direction parallel to the axis of rotation of the workpiece. When turning the end face or cutting off the workpiece, the turning tool moves horizontally in the direction perpendicular to the axis of rotation of the workpiece. If the movement path of the turning tool forms an oblique angle with the axis of rotation of the workpiece, a conical surface can be machined. For turning the surface of the formed body of revolution, the forming tool method or the tool nose trajectory method can be used. During turning, the workpiece is driven by the spindle of the machine tool to rotate for the main movement; the turning tool clamped on the tool holder performs the feeding movement. The cutting speed v is the linear speed (m/min) at the contact point between the surface of the rotating workpiece and the turning tool; the depth of cut is the vertical distance (mm) between the surface to be machined and the machined surface of the workpiece during each cutting stroke. For parting and forming turning, it is the contact length (mm) of the turning tool and the workpiece perpendicular to the feed direction. The feed rate represents the displacement of the turning tool along the feed direction (mm/rev) when the workpiece is rotated once, and can also be expressed by the feed rate of the turning tool per minute (mm/min). When turning ordinary steel with high-speed steel turning tools, the cutting speed is generally 25-60 m/min, and the carbide turning tool can reach 80-200 m/min; when using coated carbide turning tools, the maximum cutting speed can reach 300 m/min. m/min or more.
Turning is generally divided into two categories: rough turning and fine turning (including semi-finishing). Rough turning strives to use a large depth of cut and large feed to improve turning efficiency without reducing the cutting speed, but the machining accuracy can only reach IT11, and the surface roughness is Rα20 ~ 10 microns; semi-finishing and finishing Try to use high speed and small feed and depth of cut, the machining accuracy can reach IT10 ~ 7, and the surface roughness is Rα10 ~ 0.16 microns. High-speed precision turning of non-ferrous metal parts with finely ground diamond turning tools on a high-precision lathe can make the machining accuracy reach IT7-5, and the surface roughness is Rα0.04-0.01 microns. This kind of turning is called "mirror turning". If the concave and convex shapes of 0.1 to 0.2 microns are repaired on the cutting edge of the diamond turning tool, the surface of the turning will produce extremely fine and neatly arranged stripes, which will show a brocade-like luster under the action of light diffraction. As a decorative surface, this turning is called "Rainbow Turning".

During turning processing, if the turning tool rotates in the same direction with the workpiece at the corresponding speed ratio (the tool speed is generally several times the workpiece speed) while the workpiece is rotating, the relative motion trajectory of the turning tool and the workpiece can be changed, and the workpiece can be processed. Workpieces with polygonal cross-sections (triangular, square, prismatic, hexagonal, etc.). If a periodic radial reciprocating motion is added to the tool holder with respect to each revolution of the workpiece while the turning tool is longitudinally fed, it is possible to machine cams or other surfaces with non-circular cross-sections. On the shovel tooth lathe, the flank surface of the teeth of some multi-tooth tools (such as forming milling cutters and gear hob cutters) can be processed according to a similar working principle, which is called "shovel back".