What is the difference between CNC machining 3-axis, 4-axis and 5-axis?

What is the difference between CNC machining 3-axis, 4-axis and 5-axis?
15 de February de 2023 Sofía Sánchez

Modern CNC milling machines are amazing tools, capable of manufacturing prototypes and production parts quickly and reliably. To do this they must be able to move along several axes of travel while maintaining dimensional accuracy.

Therefore, we classify CNC by the number of axes with which they operate, the most common being 3-, 4- and 5-axis milling machines. These movements determine the characteristics of the parts that can be manufactured and also affect production efficiency and accuracy. In general, the more degrees of freedom available, the more complex the geometries that can be produced. To see if CNC machining is right for your next project, let’s explore the advantages and uses of these different types.


Gestión de Compras has a wide experience working with 3, 4, 5 and up to 9 axis machining. Do not hesitate to contact us to request a free quote for your next project.

How is the movement of a CNC machine?

Obviously, we are not talking about the machine itself getting up and going. Rather, we are describing the motion of the cutting tool in relation to the workpiece, which is what matters here.

First, how do we determine which axis is which? Imagine you’re looking at a typical 3-axis CNC milling machine. From your reference point, the X-axis will be parallel to the front of your body, moving from left to right. The Y-axis is the direction perpendicular to you, forward and backward, while the Z-axis is vertical.

On a typical milling machine, the worktable moves in the X/Y plane. The spindle, which holds the cutting tool, moves about the Z-axis. Note also that the cutting tool rotates on the spindle, but this rotational motion is not considered an axis of motion.

Together, the range of these motions defines a three-dimensional space, a cubic volume, within which the machine performs the cutting operations.

What is a 3-axis milling machine used for?

We use 3-axis machines every day for a wide variety of milling operations. They are ideal for removing material quickly and efficiently and for producing flat or planar surfaces. These geometric shapes are called prismatic, basically rectilinear, as opposed to more organic shapes. Yes, a 3-axis milling machine can make rounded profiles, but it is not ideal for this task.

3-axis milling machines are often used for drilling and tapping holes, but only along the Z axis. This is because the spindle is not designed for drilling holes. This is because the spindle moves up and down and cannot enter the workpiece from the side. This is a limitation for many parts that need holes or cavities machined on multiple faces, which the 3-axis machine cannot normally access.

Of course, this limitation can be overcome if the part is removed from the worktable and then repositioned. It is acceptable if there is no other choice, but then the part must be re-indexed. This means using probes to establish a new datum before machining can be restarted.

This is a slow process and there is a real possibility of dimensional errors. Therefore, whenever possible, removing a part from its fixture and repositioning it in the middle of a job should be avoided.

What are the advantages of a 4-axis CNC milling machine?

The addition of a fourth axis of motion opens up many new machining possibilities. Typically, this is accomplished by adding rotational motion along the X-axis. Such additional rotation along the X-axis is called the A-axis.

The rotary table allows the machinist to mount a part at one end and then rotate it to access the remaining sides of the part. This avoids the problem of remounting and indexing, as would occur on a 3-axis milling machine. Because the part is partially suspended, i.e., it does not touch the worktable surface, it is now possible to drill holes or other features that fully penetrate the part.

More importantly, the rotation of the workpiece while machining opens up the possibility of more complex curves and contours. A part can even rotate as on a lathe, creating cylindrical and spherical profiles. However, the 4-axis milling machine is not optimized for this type of operation, so it will be slower than if it were done on a dedicated lathe.

What are the advantages of a 5-axis CNC milling machine?

You can add yet another degree of freedom, this time along the Y axis. The rotation around the Y-axis is called the B-axis.

To achieve five axes of freedom, a 3-axis milling machine can be retrofitted with a tramming head. This is an auxiliary attachment that provides motion in the A and B axes. Along with the other capabilities of a 3-axis milling machine, it is now possible to manufacture more sophisticated shapes, such as helical rotors. These have complex compound curves in multiple directions that can only be made on a 5-axis machine.

However, a 3-axis machine with a tramming head has a limitation. On the one hand, a 5-axis machine is usually much stiffer. This is because it has to maintain accuracy even while moving in many directions simultaneously. This accuracy means tighter tolerances even for relatively simple parts.

Is there machinery with more axles?

The answer is yes. In the quest to manufacture increasingly sophisticated parts quickly and with minimal setups, CNC machining centers are greatly expanding their capabilities. Nine-axis machines combine lathe and milling functions with advanced robotics to offer all-in-one solutions. However, they tend to be large and expensive to operate. These machines are typically used for aerospace, military or scientific applications.

For most products, 5 axes are sufficient to manufacture parts with very tight features and tolerances. Here’s what you can expect if you contact Purchasing Management for a free quote on your next CNC rapid prototyping or manufacturing project.


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