What is a Turning Operation in CNC Machining?(angle milling cutter Uriah)

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Turning is one of the most common and important machining processes used in manufacturing. It involves rotating a workpiece while a single-point cutting tool is fed linearly against it to cut away material. This produces cylindrical shapes and often machined parts like shafts, bushings, pins, etc. Turning operations can be performed on dedicated lathe machines or on CNC machining centers equipped with live tooling and a rotating C-axis.
How Does Turning Work?
The workpiece, usually a cylindrical bar of material, is held and rotated by a spindle. The cutting tool is held rigidly in the tool post and fed horizontally or parallel to the axis of the workpiece. The depth of cut is set by moving the cutting tool perpendicular to the axis of rotation. As the workpiece rotates, the cutting tool removes material from the outside diameter of the workpiece to achieve the desired shape and dimensions.
On a manual lathe, the cutting parameters are set manually via levers and dials. On a CNC lathe or turning center, the process is automated via computer numerical control (CNC) programming. CNC allows fast, precise control of the cutting tool path and cutting parameters like feed rate, speed, and depth of cut.
Types of Turning Operations:
- Facing - machining the end face of a cylindrical part
- Straight turning - machining the outside diameter of a cylindrical part
- Taper turning - machining a tapered diameter
- Grooving - machining grooves on the OD or face
- Boring - enlarging existing holes to precise diameters
- Drilling - machining holes axially on the face or OD
- Threading - cutting external or internal threads
Turning Methods:
There are two primary methods of turning - longitudinal turning and face turning:
Longitudinal Turning:
Also called straight turning, this is the most common turning operation. It is used to reduce the diameter of a cylindrical workpiece to a desired dimension. The cutting tool moves parallel to the axis of rotation to remove material from the outer diameter. Depth of cut is applied via the cross slide.
Face Turning:
This method is used to machine surfaces perpendicular to the axis of rotation, like the face of a cylinder or disc. The cutting tool is fed radially across the face of the rotating workpiece to remove material.
Turning Operations on a CNC Lathe:
On a computer numerically controlled (CNC) lathe, turning operations can be programmed to automate machining complex parts. Common CNC turning functions include:
- Roughing - removing the bulk of material efficiently at high feeds
- Facing - machining the face of the part to length
- Finishing - final pass at optimum cutting parameters for best surface finish
- Tapering - programming the taper angle and turning to that specification
- Threading - single or multi-start, internal or external threads cut via CNC program
- Grooving/parting - cutting grooves and separating finished parts from the stock
- Drilling/boring - programming hole positions and cutting them on the lathe
- Lubricating - mist cooling and lubricating fluids applied via CNC program
The CNC lathe automatically controls the cutting tool location, feed rates, spindle speeds, depth of cut, and other parameters according to the program. This allows fast, consistent production of precision turned parts.
Tooling for Turning Operations:
The most common turning tool is the single point cutting tool, made of a hard material like high speed steel, carbide, ceramic, cubic boron nitride (CBN), or diamond. It consists of a properly shaped insert brazed onto a tool holder block. Common insert shapes include triangular, square, round, and diamond profiles. The tool geometry includes angles like rake, relief, and cutting edge. These factors determine cutting performance.
In addition to single point tools, turning can utilize form tools, inserts, boring bars, parting/grooving tools, thread chasers, drills, and more. On a CNC machine, live tooling like milling cutters, drills, and taps can be used in conjunction with turning to mill features on the workpiece without unchucking.
Turning Applications:
Turning is an extremely versatile process used across many industries to produce a variety of parts. Typical applications include:
- Automotive - engine crankshafts, transmission gears, driveshafts
- Aerospace - turbine engine shafts, fuselage parts, nozzles
- Medical - implants, surgical instruments, prosthetics
- Industrial - pump shafts, valves, couplings
- Consumer - rollers, screws, spindles, fittings
Almost any part with cylindrical features can benefit from turning operations. It is ideal for high volume production thanks to the fast material removal rates,ability to automate on CNC machines, and flexibility to create various features in a single setup.
Advantages of Turning:
Compared to other machining processes like milling, turning offers the following benefits:
- Excellent dimensional accuracy and surface finishes
- Ability to machine hard materials like hardened steel
- Shorter cycle times due to high material removal rates
- Higher automation with CNC turning centers
- Single setup production of complete parts
- Lower costs compared to grinding in many cases
- Minimal wasted material compared to milling processes
Turning is likely to remain a dominant manufacturing process due to its efficiency and versatility in machining cylindrical and disc shaped components. Continued advancements in CNC technology, cutting tools, and automation will only expand turning capabilities for future manufacturing needs. CNC Milling