Choosing a rotary table bearing looks simple on a spec sheet: pick a bore size, check a load rating, place the order. In practice, the YRT family — together with its YRTS and YRTM variants — behaves very differently from ordinary crossed roller or ball bearings, and the most expensive mistakes are made before the purchase order is ever signed. A bearing that is undersized for tilting moments, mounted against an insufficiently flat face, or paired with the wrong drive concept will shorten the life of an otherwise excellent machine. This guide walks through the selection process step by step, the same way our engineers approach it when a customer asks us to size a bearing for a new rotary table.

What Is a Rotary Table Bearing?

A rotary table bearing of the YRT type is a combined axial-and-radial roller bearing in which axial loads, radial loads, and tilting moments are carried by separate, precisely matched roller rows inside a very compact section height. Unlike a standard thrust bearing, it is delivered pre-adjusted and preloaded: the running accuracy is built in at the factory, and no on-site clearance adjustment is required during mounting.

This is what makes the YRT design attractive for machine tool rotary tables, vertical grinding heads, indexing stations, turret heads and precision turntables: the bearing supports the table directly, keeps axial and radial runout to a few microns, and remains extremely rigid even under combined loading. For an overview of how these bearings compare with large slewing rings, see our guide to slewing bearing applications.

Step 1: Know the Three Variants — YRT, YRTS and YRTM

The first selection decision is not size — it is which of the three variants matches your drive and control concept:

• YRT (standard series). The general-purpose rotary table bearing. It carries axial loads, radial loads, and tilting moments in a rigid, factory-preloaded arrangement and suits gear-driven or worm-driven tables where rotation is moderate and smooth. Typical uses include machining center rotary tables, milling heads and welding positioners. Standard bores run from 50 mm (YRT50, 50 × 126 × 30 mm) up to 1030 mm (YRT1030); popular mid-range sizes include the YRT80 (80 × 146 × 35 mm) and YRT100 (100 × 185 × 38 mm).
• YRTS (high-rigidity series). Externally similar, but with a modified axial roller arrangement that gives noticeably higher axial stiffness and lower, more uniform friction. This variant is intended for tables driven directly by torque motors, where high acceleration, fast reversals, and precisely limited drive torque are the norm — a common choice for five-axis machining centers and rotary indexing with short cycle times.
• YRTM (measuring series). A YRT bearing with an integrated angular measuring system. The scale is built into the bearing itself, so the rotary axis receives a true position signal without a separate angle encoder mounted around the table. Select this variant whenever the control loop requires direct, high-resolution measurement of table angle — typical in precision machining and metrology equipment.

Choosing the wrong variant here cannot be fixed later: a torque-motor table built on a standard YRT will feel sluggish and may overheat the drive, while paying for an integrated measuring system that the controller never reads is wasted budget.

Step 2: Define the Load Case Honestly

YRT bearings are selected primarily on three load components, and the relative proportions matter more than the absolute numbers:

• Axial load is usually dominant — the weight of the table, the workpiece and any fixtures, plus cutting forces pressing down.
• Radial load is typically smaller: peripheral cutting forces, belt or gear pretension, and imbalance from off-center workpieces.
• Tilting moment arises whenever the center of gravity of the load sits away from the rotation axis, or when cutting forces act at the table edge. This is the parameter most often underestimated in selection.

Also be honest about the duty cycle. Most rotary tables rotate slowly, index frequently, or oscillate rather than spin continuously — which means the static load ratings and the rigidity of the bearing are usually decisive, not fatigue life. If your application genuinely runs continuously at speed, say so early; it pushes the selection toward YRTS and changes the lubrication question.

A practical tip: write down the maximum workpiece mass and its maximum offset from the table center, not just a single “table load” figure. Those two numbers let any bearing supplier calculate the real tilting moment in minutes, and they eliminate most sizing disputes before they start.

Step 3: Get the Size, and the Envelope

Bearing size is driven by the table diameter, but the logic is not “bigger is safer.” The YRT series steps through defined bore sizes, and each step up brings:

• higher axial and radial load capacity and greater tilting-moment reserve,
• higher stiffness and better damping,
• but also a larger section height, more friction torque, and higher cost.

Check three things before committing: the available axial space in your housing design, the bolt circle you can actually machine on the table, and the drive torque your motor can deliver after friction. An oversized bearing squeezed into an undersized housing creates more problems than a correctly sized one with a sensible load reserve of 20–30 percent. Within the standard program, the small and mid sizes (YRT50 to YRT260) cover most machine tool tables, while the large sizes serve vertical lathes, radar mounts, and heavy indexing fixtures.

Step 4: Match Accuracy to What the Machine Really Needs

YRT-type bearings are precision components, and their accuracy is specified by radial and axial runout limits. It is tempting to order the highest grade available, but the sensible approach is to let the machine requirement decide:

• General indexing and positioning tables work well with standard grades; runout in the range of a few microns is already far better than most table structures can hold.
• Machining applications with tight contouring tolerances — five-axis cutting, precision grinding — justify higher accuracy grades and, frequently, the YRTM measuring variant for closed-loop control.
• Metrology and inspection equipment should combine a high accuracy grade with a stiff drive and a thermally stable environment, because at this level the structure, not the bearing, becomes the limiting factor.

Remember that achieved runout at the table edge also depends on the flatness of the mating faces. A perfect bearing bolted to an unflat table will inherit that error permanently.

Step 5: Plan Mounting, Sealing and Lubrication Upfront

YRT bearings are delivered ready-to-fit and pre-greased, but the surrounding design still decides whether they reach their rated life:

• Mating faces. Specify flatness and surface finish for the table and housing faces, and provide a locating face or pilot so the bearing rings sit concentric before bolting.
• Bolting. Follow the recommended screw size, grade and tightening sequence. Uneven clamping distorts the rings and consumes the factory-set preload unevenly.
• Sealing. The bearings ship with integral seals that handle normal machine shop exposure. For heavy chip loads, aggressive coolant or wash-down environments, add labyrinth seals or air purging at the design stage rather than as a retrofit.
• Lubrication. Confirm the relubrication interval for your duty cycle and orientation. A table that mostly sits still under load needs different grease management than one indexing thousands of cycles per shift.

Quick Selection Checklist

Common Selection Mistakes to Avoid

• Sizing by bore diameter alone. Two bearings with the same bore can differ substantially in tilting-moment capacity. Always verify the moment.

• Ignoring workpiece offset. A 200 kg fixture mounted 150 mm off-center changes the load picture completely compared with a centered mass.
• Pairing a standard YRT with a torque motor and then blaming the drive for poor dynamic response — the correct variant is YRTS.
• Forgetting position measurement until the machine is assembled, at which point retrofitting an encoder around the table is costly. YRTM exists precisely for this.
• Treating mounting as a mechanic’s afterthought. Most premature failures trace back to unflat faces or uneven bolt torque, not to the bearing itself.

Final Thoughts

A rotary table is only as good as its bearing, and a proper YRT selection takes less effort than most people expect: three load numbers, a drive concept, and a clear accuracy target. If you are planning a new table or upgrading an existing one, send us the workpiece mass, its offset, and your accuracy requirement; our engineers will return a concrete recommendation, and the standard cross roller and YRT series cover most requirements from stock or with short production lead times.