Abstract: A machine tool assembly, and particularly a spindle unit therefor, is provided wherein the spindle unit is relatively small and is designed to run at rotary speeds of between 30,000 rpm's and 40,000 rpm's utilizing hydrodynamic bearings for the spindle shaft. The hydrodynamic bearings are effective to take increased loads versus similarly sized conventional metal-to-metal contacting bearings to provide a very stiff machining system even with the higher loads generated by the increased rotary operating speeds for high speed machining contemplated for the spindle unit herein. The bearings are also designed to use a water-based fluid which is compatible with the cutting fluid. Non-contacting fluid barrier seals limit and control the amount of bearing fluid leaked to the cutting fluid. Due to the compatible nature of the two fluids, small fluid leakage from the bearings will not hurt the cutting fluid. The cutting fluid circulated at an ambient inlet temperature, e.g., 70.degree. F.

Abstract: An integrated spindle and motor unit includes a housing containing both the spindle shaft and motor with hydrostatic bearings around the front and rear of the spindle shaft. The hydrostatic bearings utilize high pressure oil, preferably in the range of 1,200-1,500 psi and provide good load bearing capacity and increased stiffness for improved cutting accuracy when cutting within the full range of cutting speeds. The present spindle unit is designed to be run at high speeds. The front and rear hydrostatic bearing pads are closely axially spaced along the spindle shaft so that the dynamic stiffness of the spindle is increased to avoid resonant vibrations even at high speed operation thereof. The spindle unit incorporates a sealing system utilizing a series of non-contacting seals including a labyrinth seal and aerostatic floating ring seals which keeps bearing oil in the spindle.