CNC milling machines with five axes are simply advanced variants of regular milling machines, where the cutting tool is capable of moving along five different axes simultaneously. It’s only with this freedom of motion that certain complex geometries can be produced.

Regular 3-axis CNC mills popular among hobbyists, simply cannot move the cutting spindle in any way that will produce partial cavities and overhangs, for example, without manually adjusting the material partway through the process.

Common CNC milling materials are usually plastics, metals, resins, waxes, or wood. As the CNC mill can be equipped with just about any kind of drill bit, any material that can reasonably and safely be drilled into could also be machined.

Because of this ability to manufacture complex parts from strong, durable materials, 5-axis CNC milling is a common manufacturing and prototyping solution in the aerospace industry – an industry that undoubtedly requires high-strength, complex geometries for demanding applications.

Mathematically-inclined readers in the audience might be wondering where exactly the two extra axes come from. After all, the Cartesian coordinate system only has 3 axes – X, Y, and Z. The answer is surprisingly quite simple, 5-axis CNC adds an additional axis of rotation about each of the X- and Y-axes. These are called rotational axes while the standard X-, Y-, and Z-directions are called translational axes.

The above diagram shows five axes. A rotational Z-axis does exist in some machines, but in reality, 6-axis CNC milling machines are a rare breed, since the sixth axis adds few benefits outside of high-end or niche applications. However, they still exist, like in these 6-axis CNC machines that offer the third rotational axis.

5 Axes in a 3-Axis World

There are two mechanical ways that CNC milling machines can achieve their 5-axis prowess: either swivel the tool head or move the table (as well as the block of material).

Swivel head machines, as the name implies, can maneuver the tool head around the block of material to get into tight spaces from different angles. This approach allows for larger, heavier objects to be machined, as the block of material remains stationary throughout the process.

On the other hand, CNC milling machines that move the object on the table, also referred to as trunnions, achieve their additional two axes of freedom by rotating the table on which the material is placed. The benefit of this approach is speed and stability, although objects that are too large or heavy can’t be rotated in this fashion.

5-axis machining is a complicated but enabling technology. Some machines are purpose-built for the task and take on a continuous CNC approach. This involves continuously adjusting the cutting tool on all 5 axes to keep the bit optimally perpendicular to the cutting surface.

On the other hand, some machines, such as the Haas VF-4, can be modified by adding a trunnion to gain two additional axes. This case is the 3+2 axis approach to machining, which locks the part at a certain angle, determined by the rotational axes around X and Y, while the tool head moves in 3 axes to cut the part.

Continuous vs. 3+2 Axis Milling

The main benefit of continuous CNC: Speed. Without the need to stop cutting to reorient a part multiple times during the process, continuous 5-axis CNC can get the job done quickly. It’s worth noting, however, that a continuously-moving tool head necessitates more moving parts (i.e. more wear and tear) and requires more advanced crash detection.

In 3-axis machines, gravity and clamps working together keep an object secure while it is machined. For this reason, the part should have a minimum thickness, which depends on the material, to ensure that it won’t snap apart when machined from a certain direction. To ensure the part is secured to the mill with enough force, tools such as hydraulic clamps or zero-point vises are often employed.

When working with heavy cutting tools that send bits of material flying all over the place at high speeds, it’s quite important to ensure that the tool head doesn’t collide with the stock at an unintended location. As it turns out, keeping track of everything in 3D space is a significant programming challenge.

The Software Side

Speaking of programming challenges, converting 3D designs from CAD software files to a physical tool path is quite a feat of engineering as well. Only some of the most advanced software tools are capable of producing truly smooth real-world results.

This includes well-known tools from Autodesk’s suite of 3D tools, such as Fusion 360, but also includes programs such as hyperMILL. Some CAM software can even be used free of charge.

When does 5-axis machining make sense? It’s best for when parts need to be a certain strength, completely nonporous, or made from unique stock material. In such cases, even the most technologically-advanced DMLS 3D printer isn’t going to meet your needs.

Additionally, 5-axis CNC machining can be used to precisely modify existing objects with complicated features, which is not possible with even high-end 3D printers. With that being said, 5-axis machining isn’t a perfect solution for any manufacturer’s woes, either.

Limitations

• It is a much more involved process. Whereas 3D printers can be turned on and typically left alone, more time and attention need to be paid to the 5-axis CNC mill. This is because the stock needs to be repeatedly repositioned, the tool head needs to be calibrated and changed, and the CAM needs to be run in individual steps.
• Its geometric capabilities are still relatively limited. The most complex geometries achievable, while more intricate than what is possible with a 3-axis mill, still cannot match what could be accomplished by many 3D printers. For example, even a 5-axis CNC mill could not make a hollow sphere from solid stock.
• Material is wasted during production. Depending on the technology of a 3D printer, the CNC mill will probably waste more material (after all, it is a subtractive manufacturing process). This can sometimes be mitigated, though, as mill waste such as aluminum and steel can often be collected and recycled back into new stock.

Obviously, none of these are reason enough to avoid 5-axis CNC machining, but it’s still good to keep in mind when approaching a project that could benefit from a 5-axis approach.

If you’re an average maker, you may be lamenting your lack of a CNC machine. However, there’s no need to be sad. There are several options.

• The local university: If you are a university student or your local university collaborates with the greater community, chances are it might have a 5-axis CNC mill available for supervised use.
• Your local makerspace: Makerspaces are places that are designed to promote flourishing through creativity and try to maintain as many tools as possible to remove any barriers to creativity. If you have a membership to your local makerspace, and if they have a 5-axis CNC mill, you’ll likely be able to obtain access to it after training.
• Hire a machining service: Online and local machining services are a great way to get up to a few parts machined for a project. Many machining services exist, and most offer 5-axis capabilities.

There are also alternative ways to get the same part made with different technologies. Tons of alternatives such as metal 3D printing, 3-axis CNC, or even wooden filaments for FDM 3D printers exist and can potentially be used as a stand-in for a particular part that could otherwise be made on a 5-axis machine.

Does your part need to be made on a 5-axis CNC mill? Try Craftcloud, an online 3D printing service marketplace that compares various printing and machining technologies, each offering different materials, different prices, and multiple delivery dates. Simply upload your model, select your technology, and Craftcloud will automatically generate quotes and comparisons among different available vendors, ultimately helping you evaluate and ultimately choose from the variety of manufacturing services currently available.