Ball and roller load handling in linear guides

2024-04-24

When a ball is under load in a linear guide, it forms an elliptical contact area against the raceway. When there’s no load, the contact area is tiny—but it expands quickly as the load increases.

The ball usually experiences the highest pressure at the center of the contact area, which gradually drops off toward the edges.

Rollers, on the other hand, form a rectangular contact patch when pressing against a flat surface—larger than what you’d get with a ball. The pressure is generally evenly distributed across that surface.

However, if the roller is perfectly cylindrical, pressure tends to spike at the edges, which can lead to material fatigue or even cracking—definitely something you want to avoid.

To solve that, manufacturers use a slightly crowned shape on the roller or apply a logarithmic profile, which evens out the load distribution. This eliminates the harmful edge loads that reduce lifespan.

To ensure maximum load capacity and precision, balls and rollers are sorted to within microns—we’re talking thousandths of a millimeter here.

Roller guides can handle about 50% more static load than equivalent ball guides.

Once again, here's a video on the topic with Carry Lindholm from Bosch Rexroth: