When designing a linear motion system, there are two main choices: round linear guide rails or profiled rails. Choosing the wrong linear motion system can be a costly mistake, resulting in design or construction changes, poor machine performance, or oversized parts with higher costs. Although both round shafts and profiled rails appear to be suitable for most applications, there are usually some criteria that dictate which technology is more appropriate.
1. Load Capacity
Recommended: Profiled Linear Guide Rails
Because of the consistency between the balls and the raceways, profiled rail systems have a larger contact area than round shaft systems, resulting in higher load capacity for a given size. Profiled rails are also better suited to moment loads than round shafts, and generally have equal load capacity in all four directions. In contrast, the load capacity of a round shaft depends on the direction of the load, which is the direction of the load toward the ball bushing.
2. Rigidity of Linear Guides
Recommended: Profiled Linear Guides
The larger contact area between the balls and the raceways allows profiled rail systems to deflect less than round shafts. And, while round shaft guides can be lightly preloaded, profiled rail systems are typically given a 2% to 8% preload, which provides greater rigidity to the guide system.
3. Linear Guide Accuracy
Recommended: Profiled Linear Guides
Profiled rails typically achieve travel accuracy orders of magnitude better than round shaft guides with ground raceways and reference edges. Round shafts are valued more in this standard for their ability to handle inaccuracies (self-aligning) than for their travel accuracy.
4. Linear Guide Speed
Recommended: Profiled Linear Guides
Round shaft guides can typically achieve a maximum speed of 2 m/sec, limited by the ability to control the ball as it moves in and out of the load zone. Profiled rail bearings use more advanced recirculation methods and can achieve speeds of 5 m/sec.
5. Linear Guide Mounting
Recommended: Round Linear Guide Rails
Where profiled rails must be fully supported and mounted along their length, round shaft guides can only be supported at their ends, with a maximum length of 20 times the shaft diameter. Round shafts also do not require machined surfaces for mounting, as ball bushings inherently compensate for some misalignment, reducing the cost and time of designing and preparing mounting surfaces.
6. Linear Guide Ruggedness in Harsh Environments
Recommended: Round Linear Guide Rails
Round shafts are generally less sensitive to debris than profiled rails and are available in a variety of materials, coatings, and sealing options to withstand corrosive or abrasive contamination. These range from all steel ball bushings to assemblies consisting of stainless steel shafts with plastic bushings.
7. Maintenance Requirements for Linear Guides
Recommended: Round Linear Guide Rails
Round shafts have lower lubrication requirements due to the smaller contact area between the load-bearing balls and the running tracks.
Summary
For most applications that require linear motion, especially those industrial applications that require high precision and reliability, profiled rails are usually a more appropriate choice. The simplicity, cost-effectiveness and moderate accuracy of round linear guide rail systems make them suitable for a wide range of applications requiring smooth linear motion and moderate load capacity.
If you are interested in linear guide rails or have any questions, please contact us.