Round Shaft Or Profiled Rail? How To Choose

- Apr 21, 2018-

When designing a linear motion system, engineers have two primary choices in recirculating linear guides—round shaft or profiled rail. Choosing the wrong linear motion system can be a costly mistake, resulting in design or structural changes, poor machine performance, or oversized components with higher costs. Although both round shafts and profiled rails may appear to be suitable options for most applications, there are typically a few criteria that dictate which technology is more appropriate.

Round shaft guides were invented in the 1940’s and have been applied successfully in virtually every industry since their inception. But their limitations in rigidity forced manufacturers of precision equipment, such as machine tools, to use machined ways or cross rollers in order to achieve the required load capacities and accuracies. The introduction of profiled rail guides in the 1970’s offered a less-costly and less time-consuming alternative, providing high load capacity and high rigidity in a fairly compact envelope. But for designers, the decision regarding when to use round shafts became less clear, since profiled rail guides were suitable for many of the applications that had been the province of round shafts. As a result, decisions were, and sometimes still are, based on past successes (or failures) with a given technology. Fortunately, there are some key performance criteria that can guide the choice between round shafts and profiled rails and take the guesswork out of the initial selection.