Crossed roller bearings offer a line of contact versus a ball bearing’s points of contact, thereby creating a broader contact surface that can carry a heavier load. This provides more rigidity, less deformation and thus more accuracy compared to the point contact of balls. Because of this, crossed-roller bearings are the most accurate form of mechanical motion component.


Crossed roller bearing supported rotary ball splines are ideal when compactness and high load capacity are essential.

As rotary support bearings, both angular contact bearings, which ride on balls, and crossed roller bearings can support both axial load and radial load as both types of loading or combined loading can be expected depending on ball spline applications. An angular contact bearing achieves this with two rows of balls whereas a crossed roller bearing can do this in a single row, but with some disadvantages such as speed and wear issue as described below. 

When comparing dimensions, one is immediately struck by the difference in size between a rotary ball spline (RBS) whose rotary support bearing rides on crossed roller bearings as opposed to an RBS whose rotary support bearing rides on ball bearings, i.e. an angular contact bearing. On the spline shaft, the spline nuts are basically the same.

Crossed roller bearing supported rotary ball spline oriented vertically in SCARA robot type ‘Pick and Place’ application. Gripper is at the end of an extended arm so the spline shaft can rotate the gripper in a large circular motion. The ball screw moves the spline shaft up and down.

In each case, they ride on ball bearings. The RBS whose rotary support bearing rides on crossed roller bearings is much more compact. The reason the crossed roller bearing supported rotary ball spline takes up so much less space is that the rotary nut and spline nut is one unit. The crossed rollers are directly attached to the spline nut’s outer cylinder. In addition, the crossed roller rotary support bearing is thinner. 

Crossed rollers provide a larger contact area than ball bearings, reducing elastic deformation. Because of this greater stiffness, crossed rollers provide consistently precise movement. There is a direct correlation between the contact area of the crossed rollers and load capacity. Load capacity can be increased greatly by roller-to-raceway contact. Balls, typically, make contact at two to four points.

However, for applications that continuously rotate, crossed rollers wear out more quickly than ball bearings because more of their contact area is in use. For example, an angular contact type is a better choice for driving the spindle drive shaft of a grinding machine, a conveyor belt or a wire winder. Whereas, crossed rollers are highly desirable when the attached gripper rotates back and forth, such as moving a half or quarter rotation when changing the angle of an item.In a rotational speed comparison, the angular contact type is more advantageous than the crossed roller type. 

Comparing the two types at a standard 16 mm (the diameter of the spline) size, the crossed roller type nut is capable of 1080 rpm versus the maximum rotational speed for an angular contact type nut, which is 4000 rpm. 

Since crossed roller rotary nut technology is newer, most existing applications already use the angular contact bearing supported ball spline. That makes changing to the newer technology expensive since it’s not the same size – it’s more compact. However, most angular contact bearing supported ball splines are interchangeable, size-wise. Though outer dimensions of interchangeable rotary ball splines may be the same, there are design advantages to consider such as the number of grooves on the spline, the points of ball contact within the grooves and shaft rigidity.

Now, the choice is up to you.

Naoki Yamaguchi is Assistant Technical Manager at NB Corporation of America This e-mail address is being protected from spambots. You need JavaScript enabled to view it . In Canada, please go to www.rotoprecision.ca/.

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