CNC Turning and Milling Machining Explained

CNC Turning and Milling Machining Explained

Our customers come to us for CNC machinery when looking to create an intricate metal shape, and want to understand what the process involves.

What are CNC machining services?

CNC machining consists of two different processes: milling and turning.

CNC stands for Computer Numerical Control. This technique involves feeding a set of instructions into a machine, which then controls the lathes, mills, routers and grinders. Any excess material will be removed, creating the desired part to exact specifications as a result. 

The difference between CNC turning and milling…

Whilst both utilise the same technology to achieve results, these subtractive manufacturing methods utilise different methods to do so.

  • Turning rotates the raw material against a cutting tool. It uses primarily round bar stock for machining components.
  • Milling spins the cutting tool against a stationary raw material. It uses primarily square or rectangular bar stock to produce components.

The key difference then is which part actually moves – either the raw material or the machine itself.

What is CNC turning?

CNC turning is derived from one of the oldest and most simple forms of creating parts, calling upon the use of the lathe. So, whilst you may think of it as a relatively new technology, it has a solid background in the precision engineering world. The machines are either horizontal or vertical depending on the weight and tolerance of the workpiece and typically, the raw materials used will be round in shape. 

The main function of the CNC turning centre device is to ‘turn’ the raw material, whilst the machine’s tool will shave away excess material to create the desired, intricate end result. Initially, the material is held in place by the ‘chuck’ which spins at different speeds according to the specifications of the computer-controlled machine. 

Lathes were originally operated manually by using a series of turn wheels. As a result, these wheels would move the chuck whilst holding the raw material in order to create the friction motion required for cutting. Fast forward to the modern-day, and these machines are now controlled numerically – no longer requiring constant manual supervision from an engineer.

CNC turning is typically used to create cylindrical parts, such as hollow tubing and shafts.

What is CNC milling?

In contrast to turning in which only a single-point tool is used, CNC milling is performed using various axis. The most traditional of these being the 3-axis, allowing for three different directional movements – X, Y and Z. Restricting the process to just three directions can set a few limits to the geometry of the part that can be created, yet for the majority of projects that require milling, this remains an efficient method. 

CNC milling also offers machining on four or more axis, including the rotation of the tool. As a result, this provides an extra level of flexibility, allowing for the creation of pretty much any shape that can be manufactured via CNC machining. However, using a four-axis machine or above is more expensive than the more traditional 3-axis counterpart. To avoid unnecessary expenses, it’s vital you speak to your precision engineer beforehand to discuss your requirements in detail. 

Generally, CNC milling is utilised for the creation of more complex components – custom tooling, intricate mechanisms, enclosures and engine parts being just a few of the possible end products. 

The difference between a 4, 4+1 and 5-axis

A 3-axis machine has some limitations, and therefore 4 or 5-axis CNC machining is becoming increasingly popular. 

The 4-axis CNC machine has an additional axis included. The spindle travels along three axis: up and down, side to side, and back and forth, while the workpiece remains stationary on the machine table. The 4-axis CNC machining further rotates along the X-axis, also known as the A-axis. This extra axis allows the 4-axis CNC machining to function in situations that involve hole drilling or cut-outs.

On a 5-axis CNC machining (also known as a 4+1), the spindle and cutting tool moves along three axes. However, there are other rotations about the X-axis (called the A-axis), Y-axis (called the B-axis), and the Z-axis (called the C-axis). 5-axis machines can utilize any two of these rotational axes, depending on their configuration.

In 5-axis machining, when the cutting tool can always be kept perpendicular to the part, we have a continuous or simultaneous 5-axis machining. This process can provide a superior surface finish and allows access to hard-to-reach areas. However, it is slower than 4+1-axis machining and more expensive. Crucially, in a 5-axis machine, the job itself and the cutting tool can both move at the same time. This enables intricate designs to be created that would be challenging by other methods. However, it also involves complex software and programming which makes it an expensive and specialist option.

What about milled features on a turned part?

Small milled features such as flats and slots can often be machined on a product produced by turning equipment – depending, of course, on the size, overall complexity and type of material used. Often a project may need a combination of the two processes to achieve the desired finish. 

Which of our services do you need?

Whilst these two CNC machining techniques seem similar on the surface, they are not the same. But, together they can complement each other to create highly intricate designs – you may need to use CNC turning and milling to form the end desired result. 

Established in 1987, we’ve been providing quality bespoke components and exceptional customer service using CNC machinery services for companies in the South East and beyond ever since. From prototyping and initial drawings, right through to production and delivery of precision machined components and complex parts in various materials, our dedicated team of passionate engineers are on hand to help you achieve your desired result. 

We’re different from other engineering companies and have all our advanced machinery in-house at our West Sussex workshop, where our expert team carry out all CNC services firsthand. 

Ready to work with an expert precision engineering firm and utilise one of these CNC machining techniques? Contact the Epal team today by either emailing us at epalengineering@gmail.com or calling us directly on 1903 744352. We’ll be more than happy to discuss your individual requirements and how we can assist you. 

Epal Engineering

Here at Epal Engineering we are really proud of what we do. We are passionate about doing the best job for all of our clients and working to an extremely high standard to make sure they get exactly want they require.

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