Standard CNC lathes have two axes, X and Z. More axes are available. Special additional axes, such as C-axis and Y-axis, are designed for milling operations (live tooling) and require unique version of a standard CNC lathe.
What is much more common for CNC lathes in industry, is the double orientation of XZ axes. CNC lathes are separated as front and rear lathes. An example of a front lathe is like the conventional engine lathe. All slant bed lathe types are of the rear kind. Identification of axes in industry have not always followed mathematical principles.
Another lathe variety, a vertical CNC lathe, is basically a horizontal lathe rotated 90°. Typical axes for horizontal and vertical machine axes, as applied to turning, are illustrated in Figure 1.
A CNC machine of any type can be designed with one or more additional axes, normally designated as the secondary – or parallel – axes using the U, V and W letters. These axes are normally parallel to the primary X, Y and Z axes respectively. For a rotary or an indexing application, additional axes are defined as A, B and C axes, as being rotated about the X, Y and Z axes, again in their respective order. Positive direction of a rotary (or an indexing) axis is the direction required to advance a right-handed screw in the positive X, Y or Z axis. Relationship between the primary and supplementary axes is shown in Figure 2.