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
unitmust be highly stiff and operate at high rotational.
Spindle specifications require a rotational number of
50,000 min-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.