While milling in Rotary mode, the tool is restricted to movement along and around the rotary axis. Any linear movement that would alter the tool's distance from the centre of rotation is wrapped to the appropriate angular position, as shown here:
For example, on an C axis rotary machine, the tool can move along the Z
axis but any Y motion is converted into an angular move around the C axis.
Note that you can specify an angular co-ordinate directly in the Co-ordinate Input dialog by stating the angle. You could do this, for example, by entering C90. If you had to, you could also do this by entering a distance in the Y axis equal to one quarter of the circumference (pi times D over 4). The real use for this is when the distance to travel was originally described as a linear distance around the cylinder.
The Angular (Move menu) command lets you specify an angular move around the spindle of the machine tool, while optionally stating a new XYZ position.
As can be seen from this diagram, the current CPL and tool remain aligned with respect to each other as the tool moves to a new angular position. The co-ordinate information is always related to the current CPL, but the Angular move is always around the spindle.