Principle Axis Method
Principle Axis Method is a technique for machining curved surfaces that are encountered in molds, dies and other engineering objects. The basic idea stems from the observation that when a cylinder that models a flat end milling cutter, is moved horizontally it machines a flat surface, however, if the axis of the cylinder is inclined than the same movement results in a curved surface. The radius of curvature of the surface depends on the inclination of the axis to the surface. This observation extends to radiused end mills as well. In PAM the relationship between inclination and curvature is determined. This relationship is used to calculate the inclination and the direction of inclination at all points along a tool path, from the principle curvature of the surface.
The PAM has been tested on numerous surfaces. The method is easy to implement but must be checked for gouging. The machining experiments show that tool paths created using the PAM are upto 80% shorter than 3axis tool paths. This however, is the upper bound as not all surfaces of a part can be machined using 5axis methods.
The publication that describe the method in detail are given below:
Authors

Title

Journal

Rao, N., F. Ismail, S. Bedi 
Int. J. of Machine Tools and Manufacturing, Vol. 37, 1997, pg. 10251040 

Bedi, S., F. Ismail, M.J. Mahjoob and Y. Chen 
Toroidal Versus Ball Nose and Flat Bottom End Mills 
Int. J. of Advanced Manufacturing Technology, Vol. 13, pp. 326332, 1997 
Bedi, S., S. Gravelle and Y. Chen 
Principal Curvature Alignment Technique for Machining Complex Surfaces 
ASME J. of Manufacturing Science and Engineering, Vol. 119, pp.756765, November 1997 
Rao, N.V., S. Bedi and R. Buchal 
Implementation of Principal Axis Method for Machining of Complex Surfaces 
Int. J. of Advanced Manufacturing Technology, Vol. 11, pp:249257, 1996 