Turning Envelopes are intended for use primarily when machining parts with a non-circular cross section. The system generates a Turning Envelope by rotating the reference part or the workpiece about the turning axis (that is, about the z-axis of the Turning Envelope coordinate system), and then intersecting the outside perimeter of the rotated shape with the XZ plane of this coordinate system. The resulting chain of entities can be used to define a Turn Profile.