Limitations of Rigid-Body Design Models for Large Hydrostatic Rotary Tables: A Coupled Elasto-Hydraulic Analysis

Hydrostatic rotary tables are widely used in the machine tool industry for high-precision machining applications. The standard design approach relies on two-dimensional (2D) Reynolds finite element models that treat the bearing gap as a rigid, uniform scalar per ring. Nevertheless, at the scale of these machines, elastic deformations become comparable to the oil film thickness. In this study, a monolithic three-dimensional elasto-hydraulic model is compared with the standard 2D benchmark for a 5.5 m diameter cast iron table with two concentric bearing rings, over a load sweep (115–230 t) and six clamping-rectangle configurations. At the nominal load, the 2D model underestimates the inner-ring mean film by 21%, overestimates the minimum outer-ring film by 30%, and underestimates the pumping power by 24%, all percentages growing with load. Independently of load, clamping configuration alone produces an inner-ring film dispersion of up to 88% of the 2D value and a ring load-sharing ratio varying by a factor of 2.8. These effects are invisible to the 2D framework and, in the most compact configuration, sufficient to collapse the oil film. These results indicate that the 2D model, while adequate for preliminary sizing, cannot substitute for the coupled model when verifying guideway safety margins.