There are two main types of a recirculating THK ball guide: one that rides on round shafts and one that rides on profiled rails. Because both types are based on recirculating balls, the terminology used to refer to them is very similar and often overlaps. Here’s a breakdown of the most common terms that are used for each one.
Round Shaft Recirculating Ball Guides
Also referred to as linear bushings, ball bushings, bushes, or the generic “ball bearing.”
While “ball bearing” is the least descriptive, it is one of the most commonly used terms, and when used in the context of linear guides, it is probably referring to a round shaft bearing. Round shaft versions are the original linear recirculating ball guides and are still widely used in applications with lower loads and forces or where the environment is extremely harsh.
Profiled Rail Recirculating Ball Guides
Also referred to as guide rails, linear guides, LM guides, or profiled rails.
In these systems, the guideway has a generally square shape and is specially machined so that the load-bearing elements (either balls or rollers) run in tracks on the rail. Profiled rail recirculating guides have higher load capacities and greater rigidity than round shaft versions and are used in all types of applications, from simple pick-and-place to semiconductor equipment and machine tools.
This is the most basic specification of any linear guide. Recirculating linear guides can withstand both pure forces and moment (overhung) loads. But they are rated for two different types of load capacity: static and dynamic.
Static Load Capacity
Static load capacity (denoted C0) is the load or moment at which permanent deformation of the raceway equals 0.0001 times (0.01 percent) of the ball or roller diameter.
Dynamic Load Capacity
Dynamic load capacity (C) is the constant load, oriented normal to the load-bearing surface, at which 90 percent of a sample will operate for a defined travel distance. Dynamic load capacity is used to calculate theoretical bearing life.
Applications that use linear bearings or ball screws often require precise positioning, which means that the motion components must be rigid. And while recirculating ball guides and screws are able to carry large loads, they inherently have clearance, or backlash, due to the size and fit of the balls between the raceways. To eliminate this backlash and increase rigidity, preload must be applied.
When researching or ordering THK ball guide, be sure to contact the experts at Technico for guidance and support. Give us a call at 330-847-7000 or contact us online for more information!