Turning is one of the core processes in mechanical manufacturing, widely used to produce components for numerous industries. Turning operations generally refer to machining tasks performed on a lathe.
Based on the geometric features of the workpiece, turning operations can be categorized as follows: facing, Turning, hole machining (including drilling, boring, and reaming), grooving, parting-off, and form machining (such as threading and knurling). This article will provide a detailed introduction to these common turning operations.
Turning
Turning is a common subtractive manufacturing process. Its principle involves feeding a cutting tool axially or radially while the workpiece rotates at high speed, creating a cutting motion that removes material layer by layer.
The different sections of a turned part usually have different diameters, and the transition areas between these diameters can be shaped in various ways, such as through steps, tapered surfaces, chamfers, or complex contours. Next, we will introduce these four forms one by one.
Step Turning
Step turning is the machining of two or more cylindrical surfaces of differing diameters, with no transition between the planes, resulting in a stepped configuration.
Taper turning
Taper turning produces workpieces with conical surfaces, characterised by a smooth conical transition between two surfaces of differing diameters.
Chamfer Turning
Chamfer turning involves using a cutting tool to shape the edges of a workpiece into a beveled surface (chamfer) with a specific angle and minimal width. The chamfer angle is typically confirmed according to customer design specifications.
Contour Turning
Contour turning refers to the process where the cutting tool follows a predefined contour path to machine the workpiece into a specific profile shape, typically a non-linear outer contour surface.
Facing
Facing refers to the process of cutting the end surface of a workpiece (the flat plane perpendicular to the axis of rotation) with a cutting tool. In this process, the tool moves radially along the radius, either from the outer diameter toward the center or from the center toward the outer diameter, while the workpiece rotates at high speed. This removes material from the end surface, creating a smooth and flat reference plane.
The purpose of facing is to remove excess material, make the surface flat and smooth, and ensure that the end surface is perpendicular to the workpiece axis, avoiding irregularities. In general, workpieces are made longer than the final part, and facing is used to remove the extra portion to achieve the precise length require
Drilling
Drilling is a material removal process designed to create holes in a workpiece. This is achieved by a rotating drill bit that is fed axially to cut and remove material, forming a hole. Unlike tapping, the diameter of a drilled hole is equal to the size of the drill bit used.
Drilling serves a wide range of purposes. It is commonly used for fastening applications like bolt connections, serves as a prerequisite step for precision operations such as tapping and boring, and can also create functional features like weight-reduction holes and cooling vents.
Boring
Boring is a process that uses cutting tools (boring bars) to enlarge and finish pre-machined holes, achieving higher precision and better surface quality. Unlike reaming, boring removes excess material to provide a correctly positioned, dimensionally accurate pilot hole. It is the only process capable of correcting positional and geometric errors in holes.
Reaming
Reaming is a hole-based finishing process that primarily involves removing a small amount of material from existing holes to enhance hole accuracy and surface quality. Typically performed as the final finishing operation after pre-machining steps such as drilling or boring. Reaming can be carried out on equipment including drilling machines, lathes, and milling machines.
Tapping
Tapping is a machining method for producing internal threads on workpieces. Its principle involves using a tap tool that rotates into a pre-drilled hole. With each full rotation of the threading tool, it must simultaneously advance by one pitch length, progressively forming the internal thread. Tapping is generally categorized into manual tapping and CNC machine tapping (also known as drilling machine tapping). Before tapping, a pilot hole must be drilled. This pilot hole should be smaller than the thread diameter, upon which the tapping process is then performed.
Grooving
Grooving refers to the machining process of creating grooves with specific width and depth on a workpiece. Common grooving types include external circular grooving, internal bore grooving, and end face grooving, all achieved through relative motion between the cutting tool and workpiece. Based on groove width, grooving can be categorized into narrow grooves and wide grooves: narrow grooves are typically completed in a single pass, while wide grooves require multiple layered passes. Grooving can be performed on either a lathe or a milling machine.
Parting
Parting-off, also known as cutting off, is a machining process that uses a specialized tool to separate a section of the workpiece, typically to cut a finished part from a bar stock. This is achieved by feeding the tool perpendicularly into the rotating workpiece until the material is completely severed. A parts catcher is often employed to collect the separated component.
Threading
Thread turning is a machining method that produces threads on a rotating workpiece using a thread turning tool. The principle involves the workpiece rotating around the spindle while the tool moves axially along the workpiece. For each revolution of the workpiece, the tool advances axially by one thread pitch. Through this synchronized motion, the tool progressively cuts a thread profile that meets specifications. Generally, deeper threads require multiple passes of the tool.
Knurling
Knurling is a forming process that uses a knurling wheel with hard patterns to apply pressure to a workpiece surface, creating embossed patterns. Knurling increases friction, making it easier to grip, while also enhancing the appearance of parts. It is commonly used on tools and hardware components. Knurling patterns typically include diamond knurling, straight knurling, and mesh knurling.
Conclusion
In summary, while turning operations encompass a wide variety of techniques, they form a well-defined system. From fundamental external cylindrical and end-face machining to specialized internal bore processing and thread turning, each operation provides a precise solution tailored to specific geometric features. Understanding these operations is central to successfully implementing turning processes.
If you’re still unsure whether turning is the right choice for your parts, Xmake is a professional CNC machining provider and can help you evaluate and find the best solution. Feel free to get in touch with us.
