Tool axis direction calculation method

A tool axis direction calculation method for determining a direction vector of a tool axis when a side of a workpiece is cut by a 5-axes numerically controlled machine tool, comprising the steps of:

• determining a first normal vector at a first dividing point located between an upper surface and a curved surface of said workpiece;
• determining a second normal vector at a second dividing point located between a lower surface and said curved surface of said workpiece;
• determining an intermediate vector having a direction between said first normal vector and said second normal vector and a size equal to a radius of a tool;
• determining a first offset point from said first dividing point and said intermediate vector;
• determining a second offset point from said second dividing point and said intermediate vector;
• determining a vector connecting said first offset point and said second offset point to be said direction vector of said tool axis;
• and
• using said direction vector of said tool axis by said 5-axes numerically controlled machine tool.