In this paper, the thermal stability of a spindle with water-lubricated hydrostatic bearings was investigated. In order to improve the thermal stability of the spindle, a center bore water cooling structure was designed in the rotor. Influences of the center bore water cooling on not only thermal stability but also temperature control performance of the spindle was studied via simulations and experiments. Power losses due to water flows in the spindle were considered. Based on a derived lumped parameter model, the temperature changes of the water flow and spindle were predicted. As used in many machine tool components, it was verified that the center bore cooling are effective to improve the thermal stability of the spindle. An influence of structural change of the rotor due to the center bore on the heat capacity and time constant was investigated. As a result, the time constant in terms of the thermal characteristics is decreased due to the center bore structure. Because of this feature, the temperature control performance can be improved.

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