How Basic Ball Spline Technologies Affect Performance

Before specifying a rotary ball spline, consider whether the rotary spline nut should ride on angular contact ball bearings or crossed roller bearings. Evaluate application requirements: stroke length, velocity, applied load, mounting space, duty cycle, required life, dimensions, installation direction, environment, and accuracy. Understanding these factors will help determine the pros and cons of each technology.

A rotary ball spline combines linear and rotary motion with sub-millimeter accuracy, ideal for automation applications. Its design features a ball spline shaft, spline nut, and ball bearings. Unlike ball bushings, the spline nut rides on a grooved shaft to prevent rotation, enabling torque transfer between shaft and nut. When the shaft is fixed, radial bearings support rotation, while fixing the nut requires radial bearings on its outer diameter, which can increase assembly bulkiness.

Rotary ball splines improve efficiency by integrating a radial support bearing within the nut, eliminating the need for external bearings and reducing overall size. This compact design streamlines installation and compatibility.

Maximizing Torque 

Torque capacity depends on groove number and ball contact points. 4-groove shafts with 4-point gothic arch grooves (16 total contact points) offer higher ratings than 3-groove circular arch designs (12 points). Gothic arches eliminate clearance, minimizing deflection for precision applications. Load capacity and rigidity also improve with 4-point contact.

The Importance of Preload 

Angular backlash occurs when the spline nut and shaft have clearance, causing rotation delays or slack. Preload tightens ball-to-groove contact, reducing backlash and friction. Higher preload grades enhance rigidity, accuracy, and product life but may increase wear. Manufacturers offer standard preloads or custom options. Preloading also mitigates deformation under load, improving stability.

Shaft Characteristics Affecting Accuracy 

Symmetrical, precision-ground shafts enhance rotational speed and stability. Manufacturers classify shafts by tolerance, perpendicularity, concentricity, and material grade. Ground shafts provide higher accuracy than drawn (non-ground) variants. Accuracy grades typically include Precision (highest), High (standard), and Normal/Commercial (non-ground). Drawn shafts cost less, suit torque transfer applications, and can reach 5-meter lengths, but load capacity is reduced due to non-ground grooves.

Crossed Roller Bearings vs. Angular Contact Bearings 

Rotary spline nuts use either crossed roller or angular contact ball bearings for radial and axial load support. Crossed rollers, arranged at 90°, offer line contact for higher rigidity, load capacity, and accuracy compared to ball bearings' point contact. However, continuous rotation wears rollers faster, making angular contact bearings more suitable for continuous rotating applications (such as grinding spindle or conveyor belt drive).

Dimensions and Compactness 

Crossed roller designs are more compact, integrating rollers directly into the spline nut's outer cylinder. They excel in space-limited, high-load applications. Angular contact designs have larger footprints but support higher rotational speeds (up to 4,000 rpm vs. 1,080 rpm for crossed rollers). Retrofitting crossed roller splines may require redesign due to size differences, while angular contact types often maintain interchangeability.