How to Choose the Best Approach for Accurately Installing Parallel Rails
Deciding on the best approach for installing parallel rails often comes down to the precision the job requires. For motion systems that must deliver highly accurate movements in critical applications, it is best to prepare a shoulder as a reference edge on the machine or equipment bed along with the proper tools to prepare, align and secure the rails. When high precision is not essential, installers have more flexibility with the mounting surfaces. And if cost is a concern, alternatives to a machined reference edge are available.
Use a Reference Edge
While not mandatory, a reference edge is a well-established method of ensuring parallelism and straightness when mounting multiple rails, especially when the motion system is intended for high-precision applications. A reference edge can be defined as a precision shoulder feature that is machined into the equipment bed. With this arrangement, the rail butts up against the reference edge with a specially prepared mating surface. Installers can press the rail firmly against the reference surface and secure it with clamps, ensuring the rail remains perfectly straight and precisely in line with the intended axis of motion. From there, it’s simply a matter of fastening the rail by inserting the mounting screws and tightening them to the recommended tightening torque.
Let the System Do the Work for You
Installers do not necessarily need a specially machined fixed shoulder to ensure parallel alignment. For installers without the benefit of having a specialized mating surface, a “temporary installation” can do the trick. By securing the primary rail and then temporarily securing the secondary rail, an installer can adjust the secondary rail and align it with the primary rail, thereby achieving parallelism before the final tightening occurs.
In a temporary installation, the installer clamps the rail to the bed using a straight piece of metal as a temporary shoulder. The assembly goes on top, and the platform can be moved back and forth by hand. This design lets the structure itself center the secondary rail, removing any concern about relying solely on the bolt pattern to clamp it in place without guaranteed perfect alignment. As the equipment slides on both rails, it moves the secondary rail gently into its centered position.
Once you have cycled the carriage and moved it fully to one end, start at that end and tighten the first bolt. Then shift the carriage slightly, tighten the next bolt, and continue the process until all are snug. That’s the benefit of temporary installation; it uses the structure to help make sure your rails are parallel, aligned and will perform at their best. And, once the rails are installed with everything securely fastened, the temporary shoulder can be re-used for another assembly, saving time and costs.
Bolt the Rails Carefully
When installing the rail, tighten the bolts sequentially from one end to the other in a single direction. Tightening them back and forth can introduce slight movement, though this is less likely when working against a reference mounting surface. Because rails can deform under force, tighten them with care. Applying too much torque can introduce internal stresses in the rail or cause the rail to shift out of alignment.
Your bearing manufacturer can recommend the appropriate torque to achieve adequate holding force without overtightening. An ideal manufacturer will also provide secondary recommendations based on expected loads, vibration and overturning moments.
By following these practices, you can mount your rails with accuracy and achieve the smooth operation and long lifespan your linear motion system requires.
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