What is CNC Milling?

By Luke Smoothy | 12/11/2020


Learn more about CNC Milling in our guide to the CNC Milling process. Discover the anatomy of a CNC machine and the different types of CNC milling available.

CNC Milling is a specific type of CNC Machining, if you would like to find out more on CNC machining check out our in-depth guide. Computerised controls are used to produce a custom-designed part or product that is of high quality and precise finish. It is favoured in many industries due to its accuracy, consistency and ability for high production and uniformity. The milling process starts with a CAD drawing (computer-aided design), and it is used to control the outputs of the CNC Milling machine. CNC stands for Computer Numerical Control. This means that the milling machine is controlled by a computer. 

This guide will provide an introduction to CNC Milling, and will cover the following: 

What is a CNC milling machine?

A milling machine manufactures high-quality parts to a high level of detail and finish. CNC milling machines use rotary tools to cut away at the material, with instructions originating from the CAD file, the part design. The function and coordinates of the cutter are controlled by the milling machine's computer, with minimum human input needed to complete manufacturing. CNC milling machines are engineered to mass-produce many components from various materials and plastics. The core function of a milling machine involves mechanically cutting away at a workpiece into the desired shape.

CNC Machined Grey Anodised

How does CNC Milling work?

The CNC Milling process works by the machine reading coded instructions and then putting them into operation. It all starts with the development of a 3D CAD file representing the final part. Once completed, the design is converted into a machine-readable format. CAM (Computer-Aided Manufacturing) software then exports this to a CNC machine program, usually in G-code format, which then acts as the instructions, directing every move that the machine makes. This replicates the CAD design in the chosen material with a high level of accuracy and efficiency. 

CNC Milling can produce high and low volumes of highly complex and intricate parts using subtractive machining technology. Material is removed from a blank workpiece and the milling machine uses a rotating cylindrical tool called a milling cutter. Depending on the type of milling machine being used, the machine is able to cut in different angles and move along different axes. 

The final part will have first been designed via CAD, or Computer-Aided Design, before being inputted into the milling machine for final production. 

cnc machine machining an aluminium aerospace part

What does a CNC Milling machine do?

A CNC milling machine makes intricate parts for a number of industries, using subtractive machining technology. The milling machine cuts away at the workpiece, and, via the 3, 4 or 5 axes, crafts the final piece. Depending on the number of axes the CNC milling machine has, the more complicated and intricate the final piece can be. A CNC milling machine is used by various industries - including aerospace and medical industries - to manufacture intricate parts. 

CNC Milling Process

You can read our detailed guide to understanding the CNC Milling process here. 

Depending on various factors, some milling machines will be more appropriate than others. The complexity of the CNC milling process will be dependent on the design of the final part. The more structurally important and high-end the part or product is, the more complex the design may need to be. For example, for intricate designs that require high precision, such as medical parts or aerospace components, a more complex machine may need to be used. This is in order to achieve the final design, finish and aesthetic. Basic parts that are machined for more general use may not require such high precision or high-quality finish. Complex and intricate designs require additional milling. Often milling machines utilize either 3, 4 or 5 axes. 

For simpler designs, a fewer number of axes is needed to achieve the final design. The cutting tools are attached to a spindle that works on 3 linear axes. In general, simple geometries can utilise a 3-axis milling machine. 3-axis machines are easy to program and operate, achieving excellent accuracy at a low cost. The cutting tools in question have the ability to spin at thousands of RPM, meaning even the sturdiest of materials can be cut through with ease and accuracy. 

3-axis machines are the most common variety of milling machine and can cut vertically (Z-axis) and in an X and Y direction. However, it’s not normally possible to machine undercuts (features that cannot be accessed with a standard end mill) with a 3-axis milling machine. Therefore, more complex designs may require a more complex milling machine. 

The 4-axis milling machine is more sophisticated, with the additional ability to rotate on the X-axis (similar to a lathe). 

5-axis milling machines include rotation in both the X and Y-axis. They are the most complete milling machines available and are implemented for highly complex designs such as medical devices and implants for the medical industry, impellers and aerospace structures.

Top Tip: Read our guide How to Machine Square Corners with CNC Milling 

Types of CNC Milling

Vertical milling

With vertical milling, a 3-axis milling table is the work surface, which sits below the arm, to which a spindle is attached. 

The spindle can be stationary if a vertical turret mill is used. In this case, the table moved along both X and Y axes. Meanwhile, if a bed vertical mill is used, the table only moves along the X-axis. The spindle travels along the length of the arm, in the Y-Axis direction. 

Horizontal milling

With horizontal milling, the spindle operates horizontally as opposed to vertically and all other components are similar to vertical milling. Generally speaking, horizontal mills are best suited to heavier projects or longer projects. They are also suited to parts that require a large amount of material to be removed as the swarf falls away from the part and cutter.

Face milling

The cutting tool’s axis of rotation is perpendicular to the surface of the workpiece.

It employs face milling cutters, with teeth both on the periphery and the tool face, the latter of which is used for finishing applications. Face milling is also used to create flat surfaces and control on a finished piece. Face milling can produce higher quality finishes than other milling processes and is compatible with both vertical and horizontal milling machines.

cnc face milling aluminium block

Plain milling

The cutting tool’s axis of rotation is parallel to the surface of the workpiece. Plain milling cutters have teeth on the periphery that perform the cutting operation. Both narrow and wide cutters are used. This allows for deeper cuts, and for larger surface areas to be worked on.  A course and fine-toothed cutter are both used.  Slow cutting speeds and fast feed rates are used for the course cutter, and vice versa for the fine-toothed cutter. This enables a more detailed final part.

Angular milling

This is a milling operation where the cutting tools’ axis of rotation is at an angle relative to the surface of the workpiece. Single angled milling cutters can, therefore, produce more angular features, such as grooves, serrations or chamfers. 

Form milling

Form milling is best used for milling operations where there are more irregular surfaces involved. Contours, outlines, edges, for example, or parts with curved, flat surfaces. It employed milling cutters or fly cutters specialised for particular applications – for example, concave cutters or corner rounding cutters. Hemispherical or semi-circular designs or other similarly intricate designs with complex parts would benefit from the form milling technique. 

How much does CNC Milling cost?

The cost of CNC Milling is dependent on various factors. The costs of CNC Milling largely stem from how long it takes to machine each piece. Longer milling times could be a result of needing to remove large amounts of material or hard materials. Depending on the part design, some parts may involve more complex tools or cutting. Other factors that define the cost of CNC milling are material and part complexity. You can click here to arrange a CNC Milling quote with the team at Get It Made, otherwise find out more about our CNC Machining services.

Features of a Milling Machine

The main features of a milling machine can generally be condensed into 7 separate parts. These features include:

  • The worktable 
  • The saddle
  • Knee
  • Column 
  • Spindle
  • Arbour
  • Machine tool
  • Ram

You can read more on the CNC Milling process here.

Benefits of CNC Milling process

High quality and precision is guaranteed 

The very nature of CNC Machining as a process leaves very little room for error and high levels of accuracy and precision. This is because it operates from a computer led program, inputting 3D designs that have been developed via CAD (Computer-Aided Design). All operations are launched via a machine interface. 

The machine executes these instructions without the need for manual input. These automated processes allow for ultimate precision to ensure even the most finite and complex geometry can be technically managed. 

CNC Machined Parts Acid Etched aluminium

CNC Milling allows for high production output

The level at which CNC Machines operate means they are capable of high levels of production due to the automated processes involved. Should a part need to be produced in high volume, with every part meeting the same level of consistency in terms of quality and finish, CNC Milling, is a trusted and popular option. It is particularly easy to program and operate a 3-axis machine, achieving high accuracy at a low cost.

CNC Milling is a less labour intensive process

Using a CNC Milling Machine significantly reduces the amount of labour involved in the production process. At full capacity, the tools used in a CNC Milling machine can spin at thousands of RPM (revolutions per minute), resulting in high production output, while also being a time-saving expense. No manual processes could achieve a similar output. It’s worth noting that the simpler the design is, the less human intervention is needed. For example, if there was a complicated design that required the blank to be moved in the process, this would involve machinists to ensure the process was completed safely and securely. 

CNC Milling machines with uniformity

CNC machining tools are designed and developed to cut away at the workpiece with the highest levels of accuracy. The movement is directed from the computer program, meaning every single part is produced to the same level of accuracy. On a wider scale, parts can be produced in high volume, with the manufacturer safe in the knowledge all completed parts will be of the same standard and finish. 

Get It Made is an established bespoke manufacturing partner for high precision CNC Milling and Machining. Get in touch to discuss your project’s requirements and kick-start your manufacturing. Arrange a CNC Milling quote today and our team will get back to you in 24 hours.

Luke Smoothy

Director and Founder of Get It Made Ltd.

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