Abstract: In This paper a new idea and a new method of analyzing radial error motion of rotating axis on the conception of instant center are put forward, and the conceptions and their calculating formulas of stationary instant center line and moving insant center line, moving rotary curve and stationary rotary curve, monocircle center of gyration and monocircle rotating axle center are advanced as well accocding to the principle of differential geometry. It is indicated that the motion range of monocircle rotating axle center relative to monocircle center of gyration can express the size of radial motion error of rotating axis itself, but the moving, stationary rotary curves are corresponding to outline curves of the workpiece at turning and boring machining, their roundness error indicates the machining precision of such kinds of machine tools as lathe and boring machine. Different from the approximate measuring theory of the Unification Document of CIRP, a kind of refined measuring theory and method of rotation error is put forword in this paper.

Key words: 回转误差, 精确测量, 主轴