The most important consideration when milling at different rotary angles is to accurately home the machine. This means that Z=0 and Y=0 must be at the center axis of the rotary fixtures. The Calibrate 4th Axis manual article details how to achieve this. Next, the stock thickness must be accurately represented in the CAM software, centered about the Z-axis:

We will use this same setup for all milling operations, regardless of the rotary angle.

Milling at A=0 degrees

Milling at 0 degrees does not take any special consideration. Process as normal, and as always double-check the WCS setting and Z values in the gcode to ensure the machine will move where you expect it to.

Milling at A=180 degrees

Angles other than A=0 will utilize the "Tool Orientation" function:

Note that the Origin is at the same point as before, but the Z-axis is flipped (compared to the model origin in the upper right of the image). The correct orientation can be confirmed in the Gcode:

T2
M3 P1 S10000
G56
G0 A180.
M106 P5 S1

Once tool orientation is correctly set, process subtractive toolpaths normally:

Milling at A=** degrees

Milling at any arbitrary angle is also a straightforward matter of setting tool orientation.

There are 2 more checks that should be done before running a file:

1. Manually jog the workpiece to the angle in the Gcode file to ensure it is what you expect (namely, that the axis is rotating the right direction)
2. If the stock is at the correct angle, double check the starting depth is correct (confirming that the stock definition, and Top Height, in CAM was correct). It is easy to forget to use caution here and the tool will start milling at full depth, not considering stock corners.