In recent years, high-performance spindles are required for multi-tasking machine tools to enhance the productivity. Such spindles enable efficient rough cutting and fine finishing of a workpiece on one machine. In order to meet this requirement, a spindle unit must be highly stiff and operate at high rotational. Spindle specifications require a rotational number of 50,000min^-1 and dN value of 3,000,000, a smaller motor was downsized and an electric loss restrained by reducing the thickness of laminate sheets composing the rotor core. A direct-injection type of ultra trace quantity lubrication and a preload switching system were used for ball bearings for high rotational speed and high stiffness. We discuss how these technical requirements were met and the results of basic experiments.

1. [1] M. Weck and A. Koch, “Spindle-Bearing Systems for High-speed Applications in Machine Tools,” Ann. CIRP, Vol.42, No.1, pp. 445, 1993.
2. [2] C. Brecher, G. Spachtholz, and F. Paepenmuller, “Developments for High Performance Machine Tool Spindles,” Laboratory for Machine Tools and Production Engineering, Aachen, Germany.
3. [3] S. Nakamura and Y. Kakino, “A Performance Evaluation of Preload Switching Spindle,” J. of the Japan Society for Precision Engineering, Vol.60, No.5, 1994 (in Japanese).