Method of determining coordinate system in machining center

A machining center coordinate determining arrangement comprising:

• a spindle for rotating a tool coupled thereto for machining a workpiece, said spindle having an axis;
• a plurality of tools of different lengths in the direction of said spindle axis;
• means for coupling a tool of said plurality of tools to said spindle;
• means for resetting a particular tool coupled to the spindle to a zero point which is the origin of a mechanical coordinate axis after a tool exchange has been effected;
• means for detecting the mechanical coordinate values of a tool coupled to said spindle with respect to said mechanical zero point;
• a tool file memory for storing length data indicative of the length of each tool of said plurality of tools;
• a program memory for storing a machining program defined with respect to said program zero point;
• means for setting a reference position with respect to said program zero point at a predetermined position on a coordinate system having an origin coinciding with the program zero point;
• means for positioning a tool, coupled to said spindle, so as to coincide with said reference position;
• means for computing the mechanical coordinate values of said reference position with respect to said mechanical zero point from information provided by said detecting means;
• means for computing the mechanical coordinate values of said program zero point from said mechanical coordinate values of said reference position;
• means for correcting, when a tool is exchanged, the mechanical coordinate values of said program zero point in accordance with a difference of length between consecutively used tools by reading tool length data from said tool file memory;
• and
• means for executing said machining program using the resulting corrected mechanical coordinate values.