WHAT’S THE DIFFERENCE BETWEEN 3-AXIS, 4-AXIS & 5-AXIS MILLING?

At GPT Precision, we have a range of state of the art 3-axis, 4-axis and 5-axis milling machines. As a designer, having an understanding of which type of machine your part will be manufactured on is critical in optimising your design. When designing a CNC machined part, you might not have thought about which type of machine your part will be machined on, but the complexity and type of geometry you can design will be different for different types of machines.
The reference to axes is used to describe CNC machines which operate along multiple axis points. CNC machining is the process of removing material from a workpiece until the desired shape is configured. These machines have at least a 3 axes and operate along an XYZ plane: X axis (vertical), Y axis (horizontal), and a Z axis (depth). The 4th axis denotes the inclusion of an A axis (rotation around the X axis), and the 5th axis denotes the B axis (rotation around the Y axis).
The number of axes on a CNC machine determines the type of work it can do, the level of detail it can cut, and the workpiece locations it can manipulate. So what does this all mean? The following provides a better explanation of the differences between a 3 axis, 4 axis, and 5 axis CNC machines.
3 Axis
3 axis machining implies that the workpiece remains in the same position while the cutting tool operates along the XYZ plane to trim away material. This is suitable for parts that don’t require a lot of depth and detailing. 3 axis machining is most commonly used to produce mechanical components and is best suited for:
Automatic/interactive operation
Milling slots
Drilling holes
Cutting sharp edges
3-axis machines are typically used for machining of 2D and 2.5D geometry. Machining of all 6 sides of a part is possible in 3 axis machining.
Many complex and practical shapes can be manufactured by 3 axis CNC milling, especially when in the hands of a world class CNC machining facility. 3-axis machining is best suited to manufacture of planar milled profiles, drillings & threaded holes in-line with an axis. Undercut features are possible with the use of T-slot cutters and Dovetail milling cutters.
However, sometimes the designed feature physically cannot be manufactured by a 3-axis machine, or the feature might be more economically viable to machine with a 4 or 5 axis machine.
4-axis cnc machining
Based on the limitations of the 3-axis explained above, 4-axis and 5-axis CNC machining became more popular. The 4-axis CNC machining process encompasses the same mechanism of action. However, from its name, there is an additional axis included.
This adds a rotation about the X-axis, called the A-axis. The spindle has 3 linear axes of movement (X-Y-Z), like in 3-axis machining, plus the A-axis occurs by rotation of the workpiece. There are a few different arrangements for 4 axis machines, but typically they are of the ‘vertical machining’ type, where the spindle rotates about the Z axis. The workpiece is mounted in the X-axis and can rotate with the fixture in the A-axis. For a single fixture setup, 4 sides of the part can be machined.
Generally, 4-axis CNC machining is preferred to 3-axis CNC machining as it speeds up and improves the accuracy of the production process.
There are two types of 4-axis CNC machining: indexing and continuous.
Index 4-axis CNC machining is when the 4th axis (A-axis) rotates whilst the machine is not cutting material. Once the correct rotation is selected, a brake is applied and the machine resumes cutting.
In continuous 4-axis machining, the machine can cut material at the same time as the A-axis rotation, simultaneously. This allows complex arcs to be machined, such as the profile of cam lobes, and helixes.
4-axis machining gives us the ability to machine angled features, otherwise not possible with a 3-axis machine. Bear in mind that 4-axis machining allows a single axis of rotation per fixture setup, so all angled features must be angled about the same axes, or additional fixtures put in place.
5-AXIS MACHINING
These CNC milling machines utilise 2 of the 3 possible rotation axis, depending on the type of machine. A machine will either utilise a rotation in the A-axis and C-axis, or a rotation in the B-axis and C-axis. The rotation either occurs 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 rotational axes operate independently to each other, meaning that the workpiece can be rotated to any compound angle in relation to the cutting tool for features to be machined. However, two axes rotation at the same time as machining is not possible. 3+2 machining can produce highly complex 3D shapes. Fully continuous 5-axis machining can simultaneously rotate the two rotation axis, at the same time as machining and the cutting tool moving linearly in XYZ co-ordinates.
Continuous 5-axis machining can produce highly complex 3D shapes, not only planar compound angled features but complex curved 3D surfaces, giving us the ability to produce parts normally reserved for moulding processes.
5-axis machining gives designers a huge level of flexibility to design very complex 3D geometry. Understanding the possibilities of each type of CNC machining is essential in design of CNC machined parts. If your design needs the use of a 5-axis CNC, make the most of it!