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Advanced Milling Advances

6-Axis CNC – What Is It Exactly?

Picture of Mika Yeap
by Mika Yeap
Mar 23, 2019
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You probably know about 3-axis CNC milling. You might even be familiar with 5 axes. But did you know there's also 6-axis CNC milling? Find out about this manufacturing marvel!

6-Axis CNC

Background: 3- and 5-axis CNC Machines

A 5-axis CNC mill at work.
A 5-axis CNC mill at work. Source: CNCZone

The CNC milling machines most will be familiar with only operate on 3 axes: X, Y, and Z. This configuration is simple — just imagine a 3D printer and, instead of an extruder, it has a cutting tool that spins really really fast!

Things get even more interesting with 5-axis CNC milling machines, which additionally execute rotations about the X- and Y-axes. The benefit is the ability to keep the cutting tool perpendicular to the material surface on multiple planes. This way, you can mill forms with overhangs that would be impossible to cut with a 3-axis machine (without a pause in milling to reorient the material, that is).

And then there’s 6-axis CNC mills. The addition of another rotation axis, usually about the Z-axis this time, can cause a significant improvement in speed compared to 5-axis configurations. And that’s exactly the technological marvel we explore in this article. 

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6-Axis CNC

6-Axis Speed

A Zimmerman FZ100 portal machining centre.
A Zimmerman FZ100 portal machining centre. Source: machinery.co.uk

The primary benefit 6-axis CNC milling offers over the closely-related 5-axis configuration is faster cutting times. With an additional axis of freedom, certain tool movements and transitions can be executed with greater speed and efficiency.

It’s difficult to explain this point; you really have to see it in action yourself. Luckily for us, Zimmerman Milling, a German manufacturer of popular 6-axis milling setups, published a video comparison of 5-axis vs 6-axis milling. We highly recommend checking it out — the buttery-smooth actuations of the toolhead are mesmerizing. 

Why all the fuss, you might ask? Well, 6-axis milling can decrease cutting times by as much as 75%. Although, there is a caveat. 

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6-Axis CNC

Limitations

A complex part for which 6-axis milling would have an advantage.
A complex part for which 6-axis milling would have an advantage. Source: Ideal PMT Machine

If you’re just machining a smaller, perfect block from another perfect block of raw material, 6-axis milling doesn’t have any advantage over a 5-axis setup. After all, if the only cuts are straight (vertical), rotations about X and Y aren’t needed, anyway, let alone rotation about Z.

That said, most components produced in the industrial setting, the only place you’ll find 6-axis CNC mills, are quite complex and do require at least five axes of machining freedom. That’s when 6-axis CNC milling shines. Complex geometries, like turbines or engine blocks, are all fair game. 

Naturally, the other main limitation of 6-axis CNC milling is cost. Adding just one more rotation axis makes the resulting mill much more complex than its 5-axis counterpart. Making, using, and maintaining such a device are no cheap tasks.

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6-Axis CNC

Case Study: Zimmerman Twin Gantry for Aircraft Parts

A promotional image of Zimmerman's 6-axis toolhead.
A promotional image of Zimmerman's 6-axis toolhead. Source: Kingsbury

Zimmerman provides many of the rare 6-axis CNC mills out there. A particular use case features a different approach to 6-axis CNC that offers similar benefits.

In that case, an aircraft company commissioned a machine with two gantries, each holding a 3-axis head, to create a larger 6-axis mill. The result of such a configuration is a 35% cycle time reduction, in some cases.

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6-Axis CNC

Summary

The consumer-grade Carbide3D Nomad; far more common than any 6-axis beast.
The consumer-grade Carbide3D Nomad; far more common than any 6-axis beast. Source: MatterHackers

We thought CNC machines were already cool with three axes. Yet, as you can see, doubling that number unveils some fascinating possibilities. For now, 6-axis milling machines are rather rare, as it’s not easy to justify the complexity involved in having one extra axis of rotation. For the right niche use case, however, 6-axis CNC mills can work wonders.

Still, garage makers can rest easy. Most of the complex geometries that machines with five or more axes specialize in can be produced on a simpler, cheaper, 3-axis consumer CNC mill, too. Some consumer rigs can even handle aluminum, which provides added thermal resistance and strength. All you have to do is execute some pre-planned raw material orientation changes between milling jobs to produce a complex geometry.

And yes, we feel your pain. Many of you may crave some 6-axis action, but very few of us work in a commercial aircraft factory. Never fear: our collection of CNC articles is here.

Feature image source: ZIMMERMANN milling solutions / YouTube

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License: The text of "6-Axis CNC – What Is It Exactly?" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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