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

Therefore, CNC milling machines are classified by the number of axes they operate, the most common being 3, 4 and 5 axis milling machines. These movements determine the part features that can be manufactured and also affect productivity and accuracy. In general, the more degrees of freedom are available, the more complex the geometry can be produced.

To find out if CNC machining is right for your next project, let's explore the benefits and uses of these different types of motion.

1. How does the CNC machine tool move?

Obviously, we're not talking about the machines themselves. Instead, we are describing the motion of the cutting tool relative to the workpiece, which is important here.

First, how do we determine which axis is which? Imagine you are facing 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 perpendicular to your direction, forward and backward, while the Z axis is vertical.

On a typical milling machine, the table moves in the X/Y plane. The spindle that carries the tool runs on the Z axis. Also note that the tool rotates in the spindle, but this rotational movement is not considered an axis of motion. Together, these ranges of motion define a three-dimensional space, a cube, in which the machine performs cutting operations.

2. What is the purpose of the three-axis milling machine?

We use 3-axis machines for various milling operations every day. They are great for removing material quickly and efficiently and for making flat or flat surfaces. Known as prisms, these geometric shapes are basically straight lines rather than more organic shapes. Yes, 3-axis milling machines can machine circles
shape contour, but it is not suitable for the task.

3-axis milling cutters are usually used for drilling and tapping, but only along the Z axis. That's because the spindle moves up and down and cannot enter the workpiece from the side. This is a limitation for many parts that require holes or grooves to be machined on multiple faces, which 3-axis machines typically do not have access to.

Of course, this limitation can be overcome if the part is removed from the table and then repositioned. This is acceptable if there is no other option, but the artifact must be reindexed. This means using the probe to establish a new reference point before restarting machining.

This is a slow process that creates a very real possibility of dimensional errors. That's why, if possible, always avoid removing part of the fixture and repositioning it mid-work. 3-axis mills can make circular features, but only in
on the X/Y plane. Still, the relative simplicity of motion is good for many projects that don't require complexity but instead benefit from maximum part throughput and process efficiency.

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

The addition of a fourth axis of motion opens up many new machining possibilities, usually achieved by adding rotational motion along the X axis. This additional rotation along X is called the A axis. The turntable lets the machinist install the part on one end and then rotate it to contact the rest of the side of the workpiece. This avoids remounting and reindexing issues on a 3-axis mill. Because the part is partially suspended - that is, not touching the surface of the table - it is now possible to drill holes or other features that fully penetrate the part.

Most importantly, the rotation of the workpiece during machining opens up the possibility to create more complex curves and contours. Parts can even be turned as if on a lathe, creating cylindrical and spherical profiles. However, 4-axis mills are not optimized for this type of operation, so their speed will slower than on a dedicated lathe.

4. What are the benefits of a 5-axis CNC milling machine?

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

In order to realize the five-axis freedom, the three-axis milling machine can be equipped with a hammock head. This is an auxiliary accessory that provides motion on the A and B axes. Combined with the other capabilities of the 3-axis milling machine, it is now possible to manufacture more complex shapes such as helical rotors. These complex compound curves with multiple directions can only be done on 5-axis machines.

5. How many axes are left?

To rapidly manufacture more complex parts with minimal setup, CNC machining centers are greatly expanding their capabilities. 9-axis machines will lathe and milling capabilities combined with advanced robotics provide an all-in-one solution. However, they are usually large and expensive to operate. Such machines are typically used in aerospace, military or scientific applications. For most products, it is sufficient to have tight tolerances on feature-rich parts.