What’s the difference between 3-axis, 4-axis and 5-axis milling?

At Usinage Avantage Inc. we offer a range of state-of-the-art milling machines, with axes from 3 to 5. As a designer, it’s essential to know what type of machine your part will be manufactured on in order to optimize your design. When designing a CNC-machined part, you may not have thought about the type of machine your part will be machined on, but the complexity and type of geometry you can design varies according to the type of machine.

The main difference between 3-, 4- and 5-axis machining lies in the complexity of the movements that the part and the cutting tool can make relative to each other. The more complex the movements of the two parts, the more complex the geometry of the final machined part.


This is the simplest type of machining, in which the workpiece is fixed in a single position. Spindle movement is available in X, Y and Z linear directions.

3-axis machines are generally used for machining 2D and 2.5D geometries. Machining all 6 sides of a part is possible with 3-axis machining, but a new fixture is required for each side, which can be costly (see below). Only one side of the part can be machined with a single fixture.

Many complex and practical shapes can be produced by 3-axis CNC milling, especially when entrusted to a world-class CNC machining center. 3-axis machining is best suited to the manufacture of planar milled profiles, holes and threaded holes in line with one axis. T-slot and dovetail milling cutters are used to produce undercuts.

However, sometimes the designed feature cannot be manufactured on a 3-axis machine, or it may be more cost-effective to machine it on a 4- or 5-axis machine.

Features that are impossible to achieve with a 3-axis machine include any features that are inclined in relation to the X-Y-Z coordinate system, even if the feature itself is flat. There are two types of angular features you can design, and it’s important to understand the distinction between the two when designing parts for CNC milling.


This adds rotation around the X axis, called the A axis. The spindle has 3 axes of linear movement (X-Y-Z), as in 3-axis machining. The spindle has 3 axes of linear movement (X-Y-Z), as in 3-axis machining, plus the A axis, which is produced by rotation of the workpiece. There are various layouts for 4-axis machines, but they are generally of the “vertical machining” type, where the spindle rotates around the Z axis. The workpiece is mounted in the machine frame. The workpiece is mounted on the X-axis and can rotate with the fixture on the A-axis. With a single fixture, 4 faces of the workpiece can be machined.

4-axis machining can be used as a more economical way of machining parts theoretically possible on a 3-axis machine. As an example, for a part we recently machined, we found that using a 3-axis machine would have required two unique fixtures, costing £1,000 and £800 respectively. By using the A-axis capability of 4-axis machining, only one fixture was required, at a cost of £1,000. This also eliminated the need to change fixtures, further reducing costs. By eliminating the risk of human error, we machined the part to a high level of quality, without the need for costly quality assurance surveys. Eliminating the need to change fixtures has the added benefit of being able to maintain tighter tolerances between the features of different faces of the part. Loss of precision due to fixing and reinstallation has been eliminated.


CNC milling machines use 2 of the 3 possible axes of rotation, depending on the type of machine. A machine will use either A-axis and C-axis rotation, or B-axis and C-axis rotation. Rotation is performed either by the workpiece or by the spindle. Rotation is either by the workpiece or by the spindle.

There are two main types of 5-axis CNC machines: 3+2 machines and fully continuous 5-axis machines.

In 3+2 axis machining, two axes of rotation operate independently of each other, meaning that the workpiece can be rotated to any compound angle relative to the cutting tool for the features to be machined. However, it is not possible to rotate both axes at the same time as machining. 3+2 machining can produce highly complex 3D shapes. Fully continuous 5-axis machining can rotate both axes simultaneously, with machining and the cutting tool moving linearly in XYZ coordinates.

Continuous 5-axis machining enables us to produce highly complex 3D shapes, not only flat elements with compound angles, but also complex curved 3D surfaces, giving us the ability to produce parts normally reserved for molding processes.

At Usinage Avantage Inc. 5-axis machining offers designers enormous flexibility in designing highly complex 3D geometries. Understanding the capabilities of each type of CNC machining is essential to designing CNC-machined parts. If your design requires the use of a 5-axis CNC, it’s important to take advantage of its capabilities! What other features could benefit from the capabilities of 5-axis machining?

At Usinage Avantage Inc. we’re working on software to simplify machining, automating large parts of the process and helping less-experienced people use CNC machines as an expert would. If you’d like to find out more, we invite you to visit our technology page to discover our solutions, watch a video about the future of our solutions, our mission and vision, or take a look at our career page!