The external circular grinding machine is a finishing machine tool which is commonly used in the machining industry. The precision of the grinding workpiece depends mainly on the accuracy and the working quality of the spindle unit of machine tools, in which the stiffness of the spindle bearing unit playsan important role. This writing presents a simulation study on effects of hydrostatic parameters with the extreme values of a hydrostatic spindle unit of an external circular grinding machine on the bearing stiffness. With the calculation method, the selected pressureregion, and the machining ability with the litmit clearance changing from 15 to 22.5µm, the stiffness of the hydrostatic spindle unit is unsatisfactory with several pump pressure values. However, in the range of pumping pressure from 2 - 5MPa, the ratio β is decisive to the stiffness, it is possible to choose a bearing diameter that is most suitable with the design requirements..

Keywords: Stiffness; hydrostatic bearing; pump pressure; radial clearance.