Abstract: The principal axis method is an advanced cutter positioning technique used for finish machining. But there are some simplifications in this method as it is used for a torus cutter. A detailed analysis about the errors caused by the simplications is presented. A precious equation of the actual cutting edge of torus is set up. The concept of the cutting edge error is brought out and its expression is also deduced, then some key factors are studied in detail. It points out that the cutting edge error is relative to the stepover of cutting path. It will limit the width of cutting strip, and a precision verification should be done when the princle axis method is used in finish machining.

Key words: Cutting edge error, Characteristic curve, Five-axis machining, Principal axis method Actual cutting edge