Turning is a CNC machining process in which a cutting tool (usually a non-rotating tool) describes a helical tool path by moving more or less linearly as the workpiece rotates.
Generally, the term “turning” is reserved for the creation of outer surfaces by this cutting action, while when applied to inner surfaces (holes of one kind or another) this same basic cutting action is called “boring” “. Therefore, the phrase “turning and boring” classifies a wider range of machining processes as turning operations. Whether using a turning tool or a boring tool, the surfaces cut on the workpiece are called “faces” and can fall into either category as a subset.
Turning can be done manually with a traditional form of lathe, which often requires constant supervision by an operator, or with an automatic lathe, which does not. Today, the most common type of this type of automation is computer numerical control, also known as CNC. (In addition to turning, CNC is commonly used for many other types of machining.)
In turning, the workpiece (a relatively rigid piece of material such as wood, metal, plastic, or stone) is rotated and the tool moves along 1, 2, or 3 axes of motion to produce precise diameter and depth. Turning can be performed on the outside or inside of a cylinder (also called boring) to produce tubular components in a variety of geometries. Although very rare now, early lathes could even be used to produce complex geometries and even Platonic solids; although the use of non-computerized toolpath control for this purpose has become unusual since the advent of CNC.
The turning process is usually carried out on lathes, which are considered the oldest machine tools, and can be of different types, such as straight turning, taper turning, copy turning or external grooving. These types of turning processes can produce materials in a variety of shapes, such as straight, tapered, curved or fluted workpieces. Generally, turning uses simple single-point cutting tools. Each set of workpiece materials has a set of optimal tool angles developed over many years.
Scrap metal fragments from turning operations are called chips (North America) or chippings (UK). In some areas they may be called lathes.
A tool’s axis of motion may actually be a straight line, or they may follow a set of curves or angles, but they are essentially linear (in a non-mathematical sense). Parts affected by turning operations may be referred to as “turned parts” or “machined parts.” Turning operations are performed on lathes that can be operated manually or with a CNC.
Specific turning operations include:
The general process of turning involves rotating the part while a single-point cutting tool moves parallel to the axis of rotation.
 Turning can be performed on both the exterior and interior surfaces of a part (a process called boring). Raw materials are generally workpieces produced by other processes such as casting, forging, extrusion or drawing.
Taper turning produces a cylindrical shape whose diameter gradually decreases from one end to the other. This can be done a) from a composite slide b) from a tapered turning attachment c) using a hydraulic copy attachment d) using a C.N.C. lathe e) using a forming tool f) by offset of the tailstock – This method is more suitable for shallow tapers.
Spherical generation generates a spherical finished surface by rotating the shape about a fixed axis of rotation. Methods include a) using hydraulic copy attachments b) C.N.C. (computer numerical control) lathe c) using forming tools (a rough and ready method) d) using bed clamps (requires drawing explanation).
Hard turning is the turning of materials with a Rockwell C hardness greater than 45. Usually performed after heat treatment of the workpiece. The process is designed to replace or limit traditional grinding operations. Hard turning, when applied for purely cutting purposes, has advantages over rough grinding. However, when it is applied to finishing operations where shape and size are critical, the grinding effect is better. Grinding produces greater dimensional accuracy in roundness and cylindricity. Furthermore, a polished surface finish of Rz=0.3-0.8z cannot be achieved by hard turning alone. Hard turning is suitable for parts requiring roundness accuracy of 0.5-12 microns and/or surface roughness of 0.8-7.0 microns. It is used in applications such as gears, syringe pump components, and hydraulic components.
Facing in turning operations involves moving the cutting tool at right angles to the axis of rotation of the rotating workpiece. This can be performed by the operation of the transverse slide, if installed, as opposed to longitudinal feed (turning). It is usually the first operation performed during the production of an artifact, and often the last one, hence the term “end”.
This process, also called cut-off or cut-off, is used to create deep grooves that remove a complete or partially complete component from its parent material.
End Grooving Grooving is similar to splitting, except the groove is cut to a specific depth rather than cutting off a complete/partially complete assembly from stock. Grooving (face grooving or trephination) can be performed on internal and external surfaces as well as on the surface of the part.
Non-specific actions include:
Enlarging or smoothing existing holes created by drilling, forming, etc., i.e. machining (generation) of internal cylindrical shapes a) Mounting the workpiece to the spindle by chuck or panel b) By mounting the workpiece to the transverse slide and placing the tool Insert the chuck. This job is suitable for castings that are too awkward to fit in a panel. On a long-bed lathe, large workpieces can be bolted to a clamp on the bed, with the shaft passing between two lugs on the workpiece that can be drilled to size. A limited application, but can be used by skilled turners/machinists.
Used to remove material from inside the workpiece. The process utilizes a standard drill bit mounted on the lathe’s tailstock or tool turret. This process can be accomplished with a separately supplied drill. Knurling uses a special purpose knurling tool to cut a jagged pattern into the surface of a part for use as a handle or as a visual enhancement. Reaming A sizing operation that removes a small amount of metal from a drilled hole. It is used to make internal holes with very precise diameters. For example, use a 5.98 mm drill bit to drill a 6 mm hole and then ream to the exact size.
Both standard and non-standard threads can be turned on a lathe using suitable cutting tools. (usually with a rake angle of 60 or 55°) on the outside or inside a hole (Tapping operation is the process of making internal or external threads in a workpiece. Often called single point threading.
Tapping nuts and holes
a) Use manual tap and tailstock center
b) Use a tapping unit with a slip clutch to reduce the risk of tap breakage.
Thread operations include
a) All types of external and internal threads using single-point tools, as well as tapered threads, double-start threads, multi-start threads, worms used in worm gearboxes, lead screws with single-start or multi-start threads.
b) Use a thread box with 4 forming tools, thread diameter up to 2″, but thread boxes larger than this can be found.
Process non-circular shapes without interrupting raw material rotation.
A lathe is a machine tool used primarily for shaping metal, wood, or other materials, producing a cutting action by having the lathe hold and rotate the workpiece while advancing a cutter head into the workpiece. For ease of identification, lathes can be divided into three types: engine lathes, turret lathes and special purpose lathes. Some smaller ones are bench mounted and are semi-portable. Larger lathes are floor-standing and may require special transportation if they must be moved. Field and maintenance shops often use lathes that can accommodate a variety of operations and are not too large to be moved from one job site to another. An engine lathe is ideal for this purpose. A well-trained operator can accomplish more machining work with an engine lathe than with any other machine tool. Turret lathes and specialty lathes are typically used in production or job shops for mass production or specialized parts, while basic engine lathes are typically used for any type of lathe work.
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