Types of linear rails.

2024-05-22

Generally, linear rails come in two main types. The most common version has through-holes where screws are inserted directly through the rail and into threaded holes in the machine base. The other version has threads on the underside, meaning you insert a screw up through the base and into the rail.

So, what’s the practical difference between these two?

Rails with through-holes are often easier to mount, especially if the machine base is thick or designed in a way that makes it tricky to insert screws from below. If you use a rail with underside threads, the base only needs simple tapped holes.

However, rails with through-holes have one major downside: they create dirt pockets around the screw plugs. Some customers don’t even bother putting the plugs in, which makes the dirt collection worse. For the sealing elements that slide along the rail, it’s nearly impossible to clean out this dirt. Lubrication from the carriage can also attract and hold onto that debris. So, it's important to always install the screw plugs!

On the other hand, rails with bottom threads have completely smooth surfaces, which makes it much easier for the seals to wipe away debris and keep the carriage’s ball bearings protected.

There’s a workaround for through-hole rails: you can install a cover strip. Some versions are glued in place, while others simply snap on. With a properly installed cover strip, the rail surface becomes smooth again, making life much easier for the seals. Snap-on versions often come with clips at the ends of the rail to keep the strip in place.

If you ever need to remove the cover strip, the snap-on ones are reusable and much easier to handle than the glued ones.

Many companies prefer cover strips over plugs because they’re faster to install and create less noise during operation.

Rails also come in standard and wide versions.h3>

In most applications, standard rails are more than enough. They can handle high lateral moments, and if needed, you can simply install two parallel rails with carriages. But for applications that fall somewhere between using one or two rails, there’s the wide rail, which can handle significantly higher lateral forces compared to the standard version.

Here’s another video on this topic with Carry Lindholm from Bosch Rexroth: