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What is CNC Milling?

What is CNC Milling

CNC milling is a machining process that uses computerized controls and rotating cutting tools to produce a custom-designed part or product. This process is used for machining a wide range of materials, such as metal, plastic, glass, and wood, and CNC machines can manufacture a variety of precision parts.

CNC, or computer numerical control, machines are programmed with a 3D CAD model, allowing machine shops to produce large amounts of identical parts. This machining process is used for a variety of parts in industries around the world. 

Early CNC machines were used in the 1940s and 1950s. This technology was replaced by analog computing technologies. From the 1960s into the 1970s, digital technologies emerged and made the production process more automated and efficient. 

This article focuses on the CNC milling process, the capabilities of CNC milling machines, and the industries it’s commonly used in.

Brief overview of CNC milling

With modern manufacturing techniques like CNC milling, the applications are nearly limitless. The milling process begins with product design using CAD (computer automated design) software.

A product designer creates a 3D model of the part and its specific dimensions. The 3D model is then converted into computer numeric controlled data that the CNC machines can understand. The data dictates how the CNC mills and lathes will move and cut away material to form the final product.

To prepare a CNC mill for production, the operator attaches the raw bar material onto the machine’s holding piece. Then the operator attaches the milling tools to the machine’s spindle to cut, drill, or shape the end product.

Once the milling machine is set up, it can be used to make high quantities of precision metal parts. These parts can be used in a variety of industries.

Some common industries and applications that utilize CNC milling include:

  • Aerospace: CNC milling is used to produce aircraft components, such as engine parts, structural elements, and landing gear, which require high precision and the use of advanced materials.
  • Automotive: The automotive industry relies on CNC milling to manufacture engine components, suspension parts, transmission components, and other critical parts that require tight tolerances and high levels of accuracy.
  • Electronics: CNC milling machines are used to create circuit boards, enclosures, and other electronic components that require precise dimensions and intricate geometries.
  • Mold-making: CNC milling is widely used in the creation of molds for plastic injection molding, die casting, and other manufacturing processes that require high-quality, precise, and durable mold components.
  • Medical devices: The medical industry uses CNC milling to produce surgical instruments, implants, and diagnostic equipment that must meet stringent quality and safety standards.
  • Energy: In the renewable energy sector, CNC milling is employed to produce components for wind turbines, solar panels, and other energy generation equipment that requires high precision and durability.

CNC machining capabilities

The milling process is best suited as a secondary machining process to provide finishing features to a custom-designed part, but finished parts can be milled from raw material. CNC milling machines allows us to machine parts of a wide range of materials, shapes, and sizes.

The capabilities depend on the type of milling machines used. CNC milling machines with greater degrees of freedom allow for increased versatility and complexity in the milled parts produced. The capabilities also depend on the machinist’s knowledge and experience.

CNC turning is a different type of machining similar to CNC milling. The main difference is that CNC milling uses a rotating tool to cut away material to form the part, while CNC turning uses a rotating part for cutting.

CNC turning is more commonly used to make cylinder-shaped parts. CNC milling can use multiple tools to cut various angles, holes, and features to machine custom precision parts.

Compare: CNC Milling vs CNC Turning

There are two types of milling machines: horizontal and vertical. The biggest difference between these two milling machines is the orientation of the spindle. With vertical milling machines, the spindle features a vertical orientation. On horizontal milling machines, the spindle has a horizontal orientation. In other words, horizontal milling machines have a cutting tool on a horizontally oriented spindle that’s removes material to form the part.

The milling machines also have slightly different cutting tools. Vertical milling machines usually have longer, thinner cutting tools, while horizontal milling machines have shorter and thicker cutting tools.


Some of the main advantages of CNC milling include:

  • High precision: CNC milling machines can achieve tight tolerances and high levels of accuracy, ensuring that parts meet the required specifications and dimensions.
  • Consistency: The computer-controlled nature of CNC milling ensures that each part is produced consistently, even across large production runs. This is particularly important in industries where quality and reliability are essential.
  • Flexibility: CNC milling machines can be programmed to create a wide range of shapes and features, making them highly flexible and adaptable to various applications and design requirements.
  • Complex geometries: CNC milling technology is capable of producing intricate and complex geometries that are difficult or impossible to create using conventional machining methods. This enables the production of advanced parts and components for various industries.


Some of the disadvantages of CNC milling include:

  • Skilled labor requirements: Operating and programming CNC milling machines require skilled and trained personnel. Finding qualified employees can be challenging, and training new staff can be both time-consuming and costly.
  • Limited material removal rate: Compared to some other machining processes, such as turning or grinding, CNC milling may have a limited material removal rate. This can lead to longer machining times for certain types of parts or materials, potentially increasing production costs.
  • Limitations with specific materials: While CNC milling machines can work with a wide range of materials, they may struggle with certain types, such as very hard materials or materials with high thermal conductivity. In these cases, alternative manufacturing methods may be more suitable.
  • Environmental impact: CNC milling machines produce waste material in the form of chips or swarf, which must be disposed of or recycled properly. Additionally, the machines typically require coolant to maintain cutting tool performance and prevent overheating, which can result in the need for proper coolant management and disposal.
  • Maintenance and downtime: CNC milling machines require regular maintenance to ensure proper functioning and to prevent excessive wear and tear. Unplanned downtime due to maintenance or repairs can disrupt production schedules and increase costs.

How precise is CNC milling?

There are many factors that influence the accuracy of CNC milling. Metal parts are typically used is a system, in conjuncture with other parts which means they need to fit together properly. If one part is too big or too small, it can mess up the entire system. Part tolerances are usually within tiny fractions of an inch, and constantly checked by a quality control team.

In some industries, such as the aerospace and medical field, maintaining tolerances is even more important.

Factors like the type of milling machine, the material being milled, the machinist’s experience, and the size of the parts can affect the level of precision.

Most CNC milling machines can typically produce parts within a 5μm tolerance. 1μm (micrometer) is 1/24500 inches. So, you can expect your parts to be very accurate.

In addition to the accuracy of the technology, modern machine shops have diligent quality control teams that complete an initial inspection. This is documented and provides the customer with an expected tolerance before production begins. Then, during production, standard quality checks are done to ensure the parts are within the desired tolerance.

A higher accuracy benefits both the machine shop and the end customer. Maintaining tight tolerances saves the machine shop time and resources because more parts are useable, and the customers receive a higher quality part.

Materials used in CNC milling

Almost any type of metal can be used for CNC milling. When selecting the right metal for your project, several factors must be considered, including the cost, strength, resistance to wear, and machinability.

At Spex, we machine a wide variety of metals and polycarbonates including: 

  • Stainless Steel
  • Aluminum
  • Brass
  • Carbon Steel
  • Copper
  • Nickel Alloys
  • Polycarbonates

You can reach out to our team if you need help deciding which material is best for your project.

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