Abstract: A fluid bearing assembly for rotatably supporting a rotary-driven spindle having smooth bearing surfaces. Each bearing has a stationary housing holding an annular bearing race that presents a smooth continuous bearing surface facing a complementary bearing surface of the spindle; together the race and spindle define a continuous, thin, uniform crevice space. The smooth race bearing surface is interrupted by a plurality of circumferentially spaced pressure generating zones, each capable of dynamically compressing a fluid body contained in the zone into the crevice in either direction of rotation of the spindle at higher speeds. Pressurized fluid is supplied to flow through each zone and out of the crevice while exerting a predetermined hydrostatic force against the spindle at lower rotational speeds.

Abstract: High speed cutting with machine tools is achieved with readily available bearings of a small diameter by mounting and presetting the cutting tool directly in a spindle of a spindle unit without employing a tool holder. Preferably, the spindle unit is small like a tool holder and can be easily changed with conventional kinds of tool changing apparatus. The elimination of the tool holder allows the conventional bearings to be kept small so that they may be operated at high speeds, e.g., 20,000 to 40,000 rpm, without excessive heat that would damage the bearings.