What is 5-axis CNC Machining?

Time: 2017-10-24

In the simplest terms, 5-axis machining involves using a CNC to move a part or cutting tool along five different axes simultaneously. This enables the machining of very complex parts, which is why 5-axis is especially popular for aerospace applications.
However, several factors have contributed to the wider adoption of 5-axis machining. These include:
A push toward single-setup machining (sometimes referred to as “Done-in-One”) to reduce lead time and increase efficiency
The ability to avoid collision with the tool holder by tilting the cutting tool or the table, which also allows better access to part geometry
Improved tool life and cycle time as a result of tilting the tool/table to maintain optimum cutting position and constant chip load

What are the Axes in 5-Axis?
We all know the story about Newton and the apple, but there’s a similarly apocryphal story about the mathematician and philosopher, Rene Descartes.

Rene Descartes. (1569-1650)

Descartes was lying in bed (as mathematicians and philosophers are wont to do) when he noticed a fly buzzing around his room. He realized that he could describe the fly’s position in the room’s three-dimensional space using just three numbers, represented by the variables X, Y and Z.
This is the Cartesian Coordinate system, and it’s still in use more than three centuries after Descartes’ death. So X, Y and Z cover three of the five axes in 5-axis machining.

What about the other two?
Imagine zooming in on Descartes’ fly in mid-flight. Instead of only describing its position as a point in three-dimensional space, we can describe its orientation. As it turns, picture the fly rolling in the same way a plane banks. Its roll is described by the fourth axis, A: the rotational axis around X.
Continuing the plane simile, the fly’s pitch is described by the by the fifth axis, B: the rotational axis around Y.
Astute readers will no doubt infer the existence of a sixth axis, C, which rotates about the Z-axis. This is the fly’s yaw in our example. 

If you’re having difficulty visualizing the six axes described above, here’s a diagram:

The A, B and C axes are ordered alphabetically to correspond with the X, Y and Z axes. Although there are 6-axis CNC machines, such as Zimmermann’s FZ 100 Portal milling machine, 5-axis configurations are more common, since adding a sixth axis typically offers few additional benefits.
One last note about axis-labeling conventions: in a vertical machining center, the X- and Y-axes reside in the horizontal plane while the Z-axis resides in the vertical plane. In a horizontal machining center, the Z-axis and Y-axis are reversed. See the diagram below:

5-Axis Configurations
A 5-axis machine’s specific configuration determines which two of the three rotational axes it utilizes. 
For example, a trunnion-style machine operates with an A-axis (rotating about the X-axis) and a C-axis (rotating about the Z-axis), whereas a swivel-rotate-style machine operates with a B-axis (rotating about the Y-axis) and a C-axis (rotating about the Z-axis).

The rotary axes in trunnion-style machines are expressed via the movement of the table, whereas swivel-rotate-style machines express their rotary axes by swiveling the spindle. Both styles have their own unique advantages. For instance, trunnion-style machines offer larger work volumes, since there’s no need to compensate for the space taken up by the swiveling spindle. On the other hand, swivel-rotate-style machines can support heavier parts, since the table is always horizontal.

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