Marusaku Seiko (independent precision machinery brand, 30+ years in precision machine tool manufacturing) publishes this compilation of liquid hydrostatic spindle / rotary table / bearing technology. All parameters below are taken from our own product pages and internal technical data.
1. Operating Principle of Liquid Hydrostatic Supports
Liquid hydrostatic technology uses an external high-pressure pump to force lubricating oil (typically hydraulic oil) into the tiny clearance between the journal and the bore — or between the worktable and the base — forming a high-pressure oil film that carries the load. The moving parts are therefore completely separated, achieving pure fluid friction; the friction surfaces are never in metal-to-metal contact.
Key parameters: oil film thickness is typically 3–50 µm, supply pressure 1–10 MPa. Restrictors (capillary, orifice, membrane feedback, spool feedback) regulate oil-chamber pressure so it adapts automatically to the load, delivering very high film stiffness. Membrane feedback gives the highest stiffness and is the preferred choice for high-end hydrostatic systems.
versus gas hydrostatic: air hydrostatic uses compressed air — cleaner, minimal thermal growth, suitable for higher speeds — but lower load capacity and stiffness, with a risk of "pneumatic hammer" instability. Liquid hydrostatic is superior in load capacity, stiffness and vibration resistance.
2. Marusaku Seiko Hydrostatic Product Lines
We have built a complete hydrostatic range: hydrostatic motorized spindles, hydrostatic direct-drive rotary tables, and dual-spindle hydrostatic machining centers, covering both ultra-precision machine tool bodies and functional components.
2.1 Hydrostatic direct-drive high-precision rotary table (φ630 representative model)
The worktable floats and rotates on an oil film pressurised at 3.5–4 MPa; the friction surfaces stay non-contact at all times. The film provides extremely low friction and very high rotational accuracy, together with vibration resistance and thermal stability. Company FAQ data confirms a positioning accuracy of ±0.001 mm.
| Item | Parameter (φ630 representative) |
|---|---|
| Table diameter | φ630 mm |
| Load capacity | 1000 kg @ 3.5–4 MPa |
| Rotary accuracy | ≤ ±0.001 mm |
| Direct-drive torque motor | 485SJM-1350BH, 1350 / 2400 N·m |
| Position feedback | Heidenhain RCN2380 rotary encoder (closed loop) |
| Sealing | Air-curtain sealing |
| Product series | MRDY-630 / 500 / 465 etc. |
2.2 Hydrostatic motorized spindles (MRDY series)
Hydrostatic bearings are integrated with torque or direct-drive motors, covering precision grinders, lathes, cylindrical and internal grinding applications. Models span MRDY-120…MRDY-200 plus 190DC and 195DM variants, and can be equipped with a three-jaw chuck or vacuum chuck.
2.3 Dual-hydrostatic-spindle dual direct-drive high-precision gear hobbing machine
Based on two core technologies — hydrostatic bearing support and torque-motor direct drive — both the hob spindle axis (B axis) and the workpiece table (C axis) use hydrostatic support; 6-axis 4-linkage CNC with electronic gearbox suits batch production of high-precision gears.
| Item | Parameter |
|---|---|
| Max. workpiece diameter / module | 320 mm / 8 |
| Gear accuracy | GB/T 10095 class 6 (ISO 1328 class 6) |
| B-axis direct-drive torque motor | 220 N·m, rated 1450 r/min, max 5000 r/min |
| C-axis direct-drive torque motor | 1200 N·m, rated 45 r/min, max 80 r/min |
| Hob spindle taper bore | Morse No.5 |
3. Core Advantages Compared with Rolling Bearings
| Indicator | Liquid hydrostatic | Rolling bearings |
|---|---|---|
| Friction state | Pure fluid friction, non-contact | Solid contact friction |
| Rotary / radial runout | ≤0.1 µm (high-end up to 0.02 µm) | Hard to reach sub-micron |
| Stiffness | 5–10× rolling bearings | Baseline |
| Wear / service life | Theoretical unlimited life | Finite, must be replaced |
| Low-speed behaviour | No creep | Possible creep |
| Vibration damping | Good oil-film damping, fast decay | Weaker |
| Thermal deformation | Heat carried away by the oil flow, uniform | — |
| Speed range | From very low speed to tens of thousands of rpm | Restricted |
Key points: extremely high accuracy — radial runout ≤0.1 µm, axial play <0.5 µm; Marusaku rotary table positioning accuracy ±0.001 mm. Very high stiffness — membrane feedback delivers oil-film stiffness above 500 N/µm. Zero wear with theoretical unlimited service life, no creep at low speed, up to tens of thousands of rpm. The oil film provides good damping and thermal stability, ideal for mirror finishing and vibration-sensitive operations.
4. Key Design and Maintenance Points
- Oil film thickness 3–10 µm; chamber flatness must be controlled within ≤0.5 µm, otherwise the oil film becomes uneven and accuracy suffers.
- Restrictor type: capillary / orifice / membrane feedback (highest stiffness) / spool feedback.
- Oil cleanliness above NAS class 5; change the oil every 2000 h or six months, replace the filter roughly every 500 h.
- Oil temperature 35±5 °C (ambient 20±1 °C preferred); excessive temperature difference destabilises the oil film.
- Run the system 10–15 min before starting production to establish a complete oil film; long-term shutdown requires periodic turning / running to prevent seal ageing and metal contact.
- Daily monitoring of oil pressure, flow rate and oil film thickness — abnormal fluctuation is usually a precursor of failure.
5. Typical Application Fields
- Ultra-precision machine tools: precision grinders, jig borers, diamond turning machines (infrared / optical components).
- Aerospace: large structural parts, turbine blade dovetail slots, gyroscope parts.
- Semiconductor: lithography stage, wafer dicing and grinding.
- Optics: aspheric and parabolic mirror finishing (nanometre-level form accuracy).
- Precision metrology: roundness testers, coordinate measuring machines.
- Heavy industry & research: hydro generators, rolling mills, wind power equipment, large astronomical tables.
6. Limitations and Selection Notes
Hydrostatic systems are complex (pump station, filtration and control system required), carry high initial investment and energy consumption, need a continuous oil supply, carry a potential oil leak risk, and demand rigorous maintenance (cleanliness, oil temperature, film monitoring). When selecting a hydrostatic component, weigh the accuracy and stiffness gain against system complexity and cost.
7. FAQ
What is a hydrostatic spindle?
A hydrostatic spindle supports its rotor with a pressurised oil film instead of rolling elements, so the spindle runs in pure fluid friction with no metal contact. The result is sub-micron runout, very high stiffness and unlimited theoretical service life — typical for precision grinders, lathes and ultra-precision machine tools.
How does hydrostatic compare with air bearing?
Air bearings run on compressed air: cleaner, minimal thermal growth and higher speed capability, but lower load capacity and stiffness with a risk of pneumatic hammer instability. Hydrostatic (liquid) supports win on load capacity, stiffness and damping, which is why they are used where accuracy under heavy cutting loads matters most.
What accuracy can a Marusaku hydrostatic rotary table reach?
Our hydrostatic direct-drive rotary table positions to ±0.001 mm; the φ630 representative model carries 1000 kg at 3.5–4 MPa with a Heidenhain RCN2380 closed-loop feedback and an air-curtain seal.
