Why the rotary table type decides your machining result
On a 5-axis machining center or a turn-mill system, the rotary table positions the workpiece on the fourth and fifth axes. Its accuracy, rigidity, and thermal behaviour set the surface finish, dimensional stability, and how long those specs hold up. Two technologies dominate the market: the conventional rolling-bearing rotary table and the hydrostatic rotary table. They look alike from the outside but behave very differently under load.
How a rolling-bearing rotary table works
A rolling rotary table supports the rotating platen on preloaded cross-roller or angular-contact ball bearings that run on hardened, ground raceways. The contact between rolling elements and raceways is finite and elastic, which brings friction, a small amount of heat, and gradual wear. Rigidity comes from the preload and the bearing diameter, and it drops once the preload relaxes or the raceways show fatigue.
How a hydrostatic rotary table works
A hydrostatic rotary table replaces metal-to-metal contact with a thin oil film a few micrometres thick. A constant-pressure pump feeds oil through restrictors into the bearing pockets; the film carries the load, separates the surfaces completely, and supplies the stiffness. With no sliding or rolling contact there is almost no friction and no wear, so accuracy does not degrade with operating hours. Heat generation stays low and the table remains thermally stable during long runs.
See the MRDY hydrostatic rotary table series for a complete product overview.
Side-by-side comparison
| Criterion | Rolling-bearing rotary table | Hydrostatic rotary table |
|---|---|---|
| Rotation accuracy (runout) | Typically several micrometres to tens of micrometres, depending on preload and size | Sub-micron class, e.g. +/-0.001 mm (1 micron) at mid size |
| Load capacity per platen diameter | Good for light to medium loads | Higher under the precision-kept oil-pressure window |
| Stiffness | Preload-dependent, relaxes over time | Oil-film stiffness, stable and predictable |
| Friction and heat | Present, causes thermal drift | Near zero, thermally stable |
| Wear and service life | Bearings wear, accuracy declines | No contact wear, accuracy retained |
| Initial cost | Lower | Higher |
| Lifecycle cost for precision work | Rises with re-preload and bearing changes | Lower over long precision use |
Reference parameters: MRDY-630
| Parameter | Value |
|---|---|
| Platen diameter | phi 630 mm |
| Rated load | 1000 kg at 3.5 to 4 MPa oil pressure |
| Rotation accuracy | +/-0.001 mm (1 micron) |
| Drive | Direct-drive torque motor, 1350/2400 N·m, 90 r/min |
| Feedback | Closed-loop rotary encoder, air-curtain sealed |
For the three metrics that actually decide a buying mistake, read hydrostatic rotary table selection: accuracy, load, torque.
Which one should you choose?
Choose a rolling-bearing rotary table when the load is light to medium, accuracy requirements are moderate, and the budget is tight. It is a sound choice for general milling and drilling where a few micrometres of runout are acceptable.
Choose a hydrostatic rotary table when the job combines heavy clamping load with tight accuracy: hard turning, fine finishing, optics, aerospace, medical, and semiconductor components. The oil film holds stiffness under load, stays thermally stable through long cycles, and keeps its accuracy for years. For environments where surface quality and positional repeatability are the real acceptance criteria, the hydrostatic design pays back through scrap reduction and stable first-pass yield. See where high-precision hydrostatic rotary tables are used.
Why Marusaku Seiko
Marusaku Seiko (MRDY) brings over 30 years of gear-manufacturing know-how to its hydrostatic rotary tables. Each unit is built to order from customer drawings, tested for rotation accuracy and oil-film stability, and supported with application engineering for turn-mill and 5-axis integration.
Request a quotation
Tell us your platen size, load, required rotation accuracy, and drive preference. We will propose a hydrostatic rotary table configuration and a delivery plan. Browse the hydrostatic product range or contact our engineering team for a tailored offer.
