Here is a pic of the Toolpath Configuation dialogue box,
Check "A-Rotations Enabled". This turns on the toolpath view to show rotary toolpaths.
"Use Radius for Feedrate" check-box turns on the Rotary Axis Feedrate Compensation.
Select which is the axis of rotation.
If you want to see the rotary toolpath displayed, then you must designate the rotary axis as "A". Mach will not display B or C as a rotary toolpath.
"Rotation Radius" DRO on the settings page is poorly named and is used by the toolpath display as well as the feedrate compensation.
This must be set to the Z axis origin offset. If the origin is at the centre of rotation, then the correct value (origin offset) is zero.
Greolt