In Mach3 we used the A axis as the rotational axis. In General Config we set the A axis as angular. Once you do that G1 A1 would rotate the A axis 1 degree. You're CAM software has to be capable of producing rotational code though. The other way to do it is to move the rotational axis using linear moves, which means you have to scale the Y axis steps per unit based on the tube diameter...and when you do that, it affects you acceleration on the axis as well.
The easiest way is to set your rotational axis to angular in Mach and use a good tube CAM software, like Hypertherm's Rotary Tube Pro. When you set the steps per unit on the rotational axis, it will be the number of steps to rotate 1 degree.