What is CNC turning?

What is CNC turning?

CNC turning is a machining process in which a rotating workpiece is held in a chuck or collet while cutting tools remove material to create the desired shape. The cutting tools move along multiple axes, determined by a computer numerical control (CNC) system, to perform operations such as turning, facing, threading, and grooving. 

What is the difference between CNC turning and CNC milling?

In the CNC turning process, the workpiece spins around an axis and the machine tool moves in a linear action. This enables cylindrical parts to be produced, as well as operations such as cutting, drilling, turning and threading. It also uses an SPTT or a single-point turning tool that’s in direct contact with the workpiece throughout the operation. 

Conversely, in CNC milling, the cutting tool spins around an axis and the workpiece moves linearly, which generates a flat surface, usually used to machine rectangular shapes. Unlike turning, the milling process relies on intermittent cutting and multiple machine steps. 

How do CNC turning machines work?

Here is a brief rundown of the CNC turning process:

• Workpiece setup. The workpiece (the object or material being machined or worked on) is securely mounted onto the machine's chuck or collet, which holds it in place for rotation during the machining process. This ensures stability and allows for precise cutting.

• Tool selection. Cutting tools, tailored to the specific machining operations, are selected and loaded into the machine's turret or toolholder. The tools may include turning tools, grooving tools, threading tools, or drilling tools.

• CNC programming. A CAD model of a specific component is imported to a CNC program, which is then loaded into the machine's computer. This program contains instructions for tool movements, spindle rotation speed, feed rates, and other parameters necessary to carry out the desired machining operations.

• Machining operations. The machine executes the programmed instructions, with the spindle rotating the workpiece while the cutting tools move along their respective axes. This process removes material from the workpiece, shaping it to the desired dimensions and features. 
  

What kind of parts can you make with CNC turning machines?

CNC turning machines are versatile tools capable of producing a wide range of parts with varying complexities. Here are some examples of parts that can be made using CNC turning:

• Shafts and axles. CNC turning is ideal for producing long, cylindrical parts used in various industries, including automotive and aerospace.

• Bushings and bearings. Precision-made bushings and bearings are vital in mechanical assemblies, reducing friction and supporting smooth rotational movement.

• Connectors and fittings. CNC turning enables the production of connectors, fittings, and couplings used in plumbing, hydraulic systems, and electrical applications.

• Fasteners. Screws, bolts, and nuts, produced with CNC turning, are essential components used in assemblies across industries for joining and securing parts.

• Valves and valve components. CNC turning allows for the creation of valve bodies, stems, seats, and intricate components used in fluid control systems.

• Tooling components. Such as inserts, toolholders, and bodies used in machining operations, enhancing efficiency and accuracy.

• Automotive parts. CNC turning is employed to create engine components, pulleys, brackets, and specialized parts for the automotive industry.

 
How do you design parts for CNC turning?

The following tips and considerations can help you design parts that are well-suited for CNC turning, resulting in efficient manufacturing and high-quality finished products.

• Material selection. Choose a suitable material for the part based on its intended application, considering factors like strength, durability, and machinability. Common materials for CNC turning include metals (such as aluminum, steel, and brass) and certain plastics.

• Design for rotation. Because CNC turning involves rotating the workpiece, ensure that the part design allows for effective rotation and machining. Avoid complex internal features or shapes that may hinder proper machining access.

• Simplify geometry. Keep your part’s design as simple as possible to facilitate efficient machining. Minimize the number of features, sharp corners, or complex curves that can increase machining time and complexity.

• Size and tolerances. Specify accurate dimensions and tolerances based on the functional requirements of the part and the capabilities of the CNC turning machine. Consult standards for recommended tolerances.

• Tool selection. Consider the selection of cutting tools for the machining operations required. Design the part to accommodate standard tool sizes and shapes, minimizing the need for custom or specialized tools.

• Avoid overhangs and thin sections. To ensure stability and prevent deflection during machining, minimize overhangs and thin sections in the design. Adequate support and rigidity will result in better machining accuracy and surface finish.

Which tool or design works best for which material?

In CNC turning, the choice of tools and designs depends on the specific material being machined. Different materials have unique properties that influence tool selection and cutting strategies. Here are a few common materials used in CNC turning and the recommended tools and designs for each. 

• Aluminum. When machining aluminum, it is recommended to use carbide or HSS inserts with sharp cutting edges. Plan to use lighter cuts, higher cutting speeds, and the use of coolant or lubrication to prevent chip adhesion.

• Low/medium carbon steel. When machining low to medium carbon steel, you should use carbide inserts with a tougher grade and a positive rake angle. Additionally, use sturdy toolholders, adequate coolant and lubrication, and a slower cutting speed compared to aluminum.

• Stainless steel. For stainless steel, it is recommended to use carbide inserts with high-temperature resistance and low friction coatings. The process also works best with lower cutting speeds, controlled feed rates, and efficient coolant and lubrication to manage heat buildup.

• Brass and copper. When machining brass and copper, use carbide or HSS tools with sharp edges and polished surfaces. Additionally, you will need adequate coolant and lubrication to prevent work hardening, lighter cuts, and controlled chip formation.

• Plastics. Machining plastics such as acrylic or Nylon requires solid carbide or HSS tools with sharp edges. You should also use lower cutting speeds, reduced feed rates, and coolant or lubrication to prevent melting or chip sticking.

• Exotic alloys. For machining exotic alloys such as titanium, specialized carbide inserts or ceramic inserts designed for high-temperature resistance are recommended. Be sure to use a rigorous coolant or lubrication system, slower cutting speeds, and a strong, rigid tooling setup.
  

Fast CNC turning with local machine shops

Protolabs Network's network of local machine shops in the US and EU makes it easier to get CNC turned parts quickly. Local manufacturing eliminates the need for your parts to clear customs, so you benefit from fewer logistical hurdles and lead times as fast as five days. 

Use Protolabs Network's CNC turning service

Find out more about Protolabs Network's CNC turning capabilities.  When you’re ready to get an instant quote for a custom part, upload a CAD file and select CNC turning as the service.

You can also read more about different types of CNC machining, including advice on material selection, surface finishes and optimizing your design.