An Introduction to CNC Turning

As the World (CNC) Turns – The Evolution of CNC Turning

Computer numerical control (CNC) turning is one of the most popular automatic machining methods used in metalworking and fabrication shops. Manufacturers use this process to create round or tubularly shaped objects from wood and metal workpieces that can later be used to form materials such as engine components, construction materials, and even art.

CNC turning operates by using a lathe machine and stationary cutting tools to precisely shape metals into specifically designed components. The practice of turning metal workpieces to create shapes can be traced back to the 1840s when Stephen Fitch introduced the turret lathe for use in fledgling American factories. Initially used to create screws, this machine operated by a worker manually cycling the workpiece through a series of automated functions in a process then known as screw machining. In the 1950s, researchers at MIT perfected the use of computerization to better automate the screw machining process; this technique became known as CNC turning.

How Does CNC Turning Work?

During CNC turning, various changeable cutting tools operate on a rapidly rotating metal workpiece, shaving the metal down to the desired size and thus reducing its diameter.

The CNC turning lathe machine consists of a stationary or sliding headstock and a guide bushing. Operators secure the metal workpiece in the headstock via a collet, which grips the metal and rotates it with a spindle. As the metal turns at high speeds, the computer sends digital instructions to the lathe machine, creating predefined sequences in which the different cutting tools on the turret operate on the workpiece. The lathe gradually trims the piece’s diameter to form the desired cross-sectional shape, which can then be used for later applications. This process is also known as subtraction machining since it involves the removal of excess material from the workpiece.

The cutting tools are generally mounted on a turret, which serves as an indexing tool holder. When a particular tool completes its operation, the turret automatically cycles to the next tool it needs, allowing it to perform many processes on the workpiece in quick succession. Turrets that hold more tools generally produce more complex parts.

CNC turning is renowned for its high level of precision and relatively fast job changeover rate. CNC turning lathe machines can rotate bar stocks at speeds of up to 10,000 rpm and can produce parts with tolerances within 0.0002–0.0005 in.

What Are the Differences Between CNC Turning and CNC Milling?

Many professionals use the terms CNC milling and CNC turning interchangeably, but they describe different processes that yield distinct outcomes. Although they are similar in theory, CNC milling and CNC turning consist of separate operations that produce a wide range of parts.

CNC milling machines hold a workpiece in place with a clamp while their rotating cutting or drilling tools gradually remove material from the piece. In contrast, CNC turning machines rotate the workpiece itself while the tools remain stationary. Since it involves less moving parts, CNC turning can produce larger volumes of material at a lower cost than CNC milling; however, CNC turning only works for materials that incorporate a cylindrical profile, meaning that CNC milling is necessary to produce a broader range of cross-sectional shapes.

Which Option Should You Choose?

Because of the differences between CNC turning and CNC milling, it is important to discuss with your vendor the specific parts your product requires along with the most efficient processes by which they can be created.

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