Characteristics of a spindle supported with water-lubricated hydrostatic bearings were experimentally investigated. In particular, this paper focuses on the thermal characteristics of the spindle. The flowrates of water as the lubricating fluid were measured separately for the radial and thrust bearings, in relation to the supply pressure. Fluid power losses owing to pressure losses of the lubricating fluid were then introduced. Furthermore, the power losses owing to the water viscosity were determined by measuring the spindle torque and angular velocity. The experiments revealed that the total power loss of the spindle is approximately 300 W. The cooling effect of the lubricating water was then examined by introducing a temperature increase between the supply and drain water. The experimental results verified that the water temperature increased by approximately 0.8°C, at a spindle speed of 3000 min^-1. Based on the temperature increase of the water, the power removed from the spindle by the water flow was estimated. By comparing the generated total power loss and the power transferred by the water flow, the cooling efficiency of the flow of lubricating-water was defined in this paper. If the cooling efficiency is 100%, the temperature change of the spindle can be zero regardless of the power loss, achieving ideal thermal stability of the spindle. Experimental results revealed that the cooling efficiency of the tested spindle was over 80%. This indicates that the flow of water as a lubricating fluid removes generated heat from the spindle effectively, and achieves improved thermal stability of the spindle.

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