Machinery Basics: What are The Axes in 5-Axis?

From Cartesian coordinates to the difference between horizontal and vertical machining centers.

In the beginning came the drill press, which gave us 1-axis machining.

The lathe gave us two axes. The knee mill gave us three.

These days, machine tools are advertised with as many as eleven axes, but 3- and 5-axis machining are the most common. But what are these axes and how do they apply to modern machine tools?

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)

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 from Hurco North America:

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-labelling conventions: in a vertical machining center, the X- and Y-axes reside in the horizontal plane while the Z-axis resides in the vertical. In a horizontal machining center, the Z-axis and Y-axis are reversed. See the diagram below:

(Image courtesy of Cameron Anderson/Aerotech.)

(Image courtesy of Cameron Anderson/Aerotech.)

For more information about 5-axis, check out The What, Why and How of 5-Axis CNC Machining.