Abstract: For solving the actual problem of machining random – space – curve in the machine – tool CNC system, the prearranged step interpolation method is presented, which is based on the computer technique, used in the real – time control case and accorded with the machining technics. Any regular curve that can be expressed by the vector parameter equation and which Frenet – frame exists may be interpolated by this method.

Key words: CNC machine tool, Interpolation, Space – curve