When specifying rotary stages, you might find yourself concentrating first on the allowable payload. But for our ServoBelt rotary stages, you shouldn't make payload your primary focus. These stages are built around duplex angular contact bearings that can handle hundreds of pounds both statically and dynamically in the axial and radial directions.

Thanks in no small part to this robust bearing architecture, our ServoBelt rotary stages combine long life and high speeds even when faced with combination loads and tight wobble and run-out requirements.

Let’s take a closer look at the important role duplex angular contact bearings play in our ServoBelt rotary stages.

Duplex Angular Contact Versus X-Type Bearings

Some precision rotary stages incorporate X-Type bearings—a design that functions in a similar way to crossed roller bearings. Although they come in handy when you have a lot of torque to work with, X-Type bearings are speed limited and have trouble with combination axial and rotary loads.

That's not to say they don't have their place. On the plus size, X-Type bearings cost about 50 percent less than a matched set of angular contact bearings. And we recently incorporated X-Type bearings into a large custom rotary stage that did not have stringent speed, precision or load requirements—saving a significant amount of cost for our customer.

While X-Type bearings can always be a low-cost option when needed, all of our standard SBR stages incorporate high-performance full duplex angular contact bearings. This design consists of two angular contact bearings whose faces have been precision ground so that the two bearings can function as one in a matched set. When clamped face to face within the rotary stage, the bearings have a preload that helps improve precision—by reducing backlash.

Unlike X-Type bearings, duplex angular contact bearings won’t hit their speed limit in typical rotary table applications. We commonly run these bearings at 1,200 rpm or even above without shortening their life expectations or introducing excess wobble or run-out. A similar X-contact bearing might have a speed limit of 500 rpm or less.

The arrangement of the two bearings—in particular, their opposing contact angles—also lets them handle combinations of loads, including moments, shear loads and axial loads. For our rotary stages—which have through holes up to 200 millimeters—the resulting bearing capacity is far above the payload masses that we can practically position. In other words, our bearings are operating at a small percentage of their total capacity—translating into virtually limitless bearing life.