A hydrostatic bearing, spindle or rotary table floats on a thin, pressurized oil film. The film supports the load and absorbs cutting forces while metal never touches metal. That film is only as stable as the oil that forms it, and oil viscosity changes with temperature. Hold the temperature and you hold the precision; let it drift and the whole machine drifts with it.
What the Oil Actually Controls
The supply unit pushes clean oil at a constant 2–4 MPa through precision restrictors into the bearing pockets. Film thickness sits in the order of a few tens of microns. Stiffness, the amount the film deflects under load, depends directly on oil viscosity. Viscosity is temperature-sensitive: a 10 °C swing can change it by 20–30 % for a typical mineral oil.
How Viscosity Drift Breaks the Geometry
When the oil thins, the film softens. The same load then produces more deflection, so runout and repeatability wander. When the oil thickens, pump work rises, heat rises, and a feedback loop develops that overshoots the setpoint. Either way the axis that held 0.5 µm yesterday holds 1.5 µm today, with no visible fault.
The Standard: Hold ±1 °C
Industrial hydrostatic systems target oil temperature control within about ±1 °C, with some builders specifying ±0.5–1 °C. The components that deliver this are a thermostatic chiller or plate heat exchanger on the return line, a small immersion or band heater for cold-start stabilization, a tank temperature sensor feeding a controller, and enough tank volume to damp short-term swings.
Why the Other Parts Matter
Precise filtration at ≤10 µm keeps the restrictors from clogging, which also protects film stability. An accumulator smooths the pressure pulses from the constant-pressure piston or gear pump, so film pressure stays steady between chiller cycles. Tie all of it together and the bearing sees a near-constant environment.
| Parameter | Typical value |
|---|---|
| Oil supply pressure | 2–4 MPa |
| Oil temperature control | ±0.5–1 °C |
| Filtration | ≤10 µm |
| Pump type | Constant-pressure variable piston / gear pump + accumulator |
Where It Fits
This is the backbone of every hydrostatic spindle, rotary table and linear guide we build. See the oil supply and pump station overview, the hydrostatic vs rolling bearing comparison and the full hydrostatic product range.
If you are specifying a hydrostatic retrofit or a new precision axis, tell us your load, speed and accuracy target and we will size the oil supply and film geometry to match it.
