Cross roller guides, needle roller guides, or recirculating ball guides? There are different types and there is a suitable linear guide for every application. In this article, we will take a closer look at cross roller linear guides. We discuss their design, features, advantages, and disadvantages. It also explores three modern cross roller linear guide designs for today's mechanical engineering applications.
Crossed roller guides are designed for limited strokes and consist of two hardened rails with a crossed roller cage for bearing support in between. The use of rolling bearings allows for a low friction coefficient of <0.003. The rollers which are 90 degrees angled to each other, are held in place by a cage. These linear guides are suitable for applications with the highest precision requirements.
The basic structure of a cross roller guide comprises two pairs of linear guides. Each cross roller guide pair consists of:
2 pieces guide rails
1 piece cross roller cage assembly
4 pieces end stops
The end stops need to be inserted at both rail ends. The roller cage assembly includes freely rotating cylindrical rollers arranged in a cross-shaped pattern at 90-degree angles to each other. These rollers make contact with the raceways of the guide rails.
Due to this roller arrangement, the cross roller guide supports loads from all directions including high overturning moments. Furthermore, unlike certain linear bearings that include linear rails and recirculating units, all the rollers in this arrangement are constantly bearing the load, except in cases of pure radial loads where only half of the rollers are engaged at any given time due to the cross-shaped arrangement.
Compared to ball-caged guides with a 4-point contact in the linear guide, crossed roller guides provide a line contact surface, enabling them to support higher loads and offer higher stiffness. Because of this, cross roller linear guides provide higher precision.
As cross roller guide offer high stiffness they are more sensitive to assembly imperfections compared to ball linear bearings. The mounting surface needs to be rigid and prepared at high precision. The assembly is a careful process. This link provides clear step-by-step instructions on how to assemble cross roller guides.
The crossed roller guides or slide ways are designed to support loads and transfer objects in a machine at high precision. Slide ways are commonly used in applications such as pick-and-place machines, microscopy and medical scanning devices, and precision machines such as semiconductor lithography and metrology.
On this page, you will find some videos showing applications of cross roller guides.
Compared to other mechanical linear bearings or guides, crossed roller guides offer the highest precision (nano-micrometer level) and repeatability while maintaining the lowest friction rate.
Cross roller linear guides are made from carbon chromium steel (100Cr6). The steel used by PM is extremely clean providing an optimum balance to achieve repeatable tight manufacturing tolerances and ensure consistently high product quality. After machining the material is through-hardened at 58-66 Hrc. The main goal of the heat treatment is to increase the strength of the material and enhance wear resistance, high load capacity, and long service life.
This link provides more information about the materials we use for the linear guides we manufacture.
Cross roller guides offer many advantages. The most important advantages are listed below.
High rigidity and precision: The cross-shaped roller arrangement in combination with the line contact on the raceway allows for high rigidity and precision. Due to the adjustable preload, the cross roller guides can be adjusted without play and thus offer high precision at the sub-micrometer level with great repeatability.
High load capacity: Due to the cross-shaped roller arrangement cross roller linear guides can handle high radial and axial loads, making them suitable for high-dynamic applications.
Almost maintenance-free: no readjustment of preload is needed, and the bearings need a minimum of lubrication. Often, 2-3 x service lubrication during the entire lifetime is needed.
Compact design: The compact design of the linear guides allows for minimal space usage. It meets the tight space design requirements of today’s industry as with benchtop devices.
Durable: Cross roller bearings are designed to be durable, withstanding high loads and extreme use 24/7.
Smooth and quiet operation: As the raceways and cylindrical rollers are precision finished they operate almost friction and noise-free. This results in an excellent smooth and uniform operation.
Even though cross-roller guides offer many advantages, there are also some disadvantages to consider.
Cost: Cross roller linear guides can be more expensive than other types of linear guides, due to their precision manufacturing, high level of straightness, and flatness of movement. Also, the mounting parts on which the bearings are mounted need to be accurately machined.
Careful assembly: As the linear guide consists of separated components (1 set = 4 guide rails + 2 roller cage assemblies + 8 end stops) the assembly needs more attention and time compared to other guides. The assembly procedure is well-documented which makes it more easier.
Limited travel: as these linear guides did not use recirculating blocks as profile rail guides do, but a flat cage that floats between a pair of rails, the travel is limited by the rail length and the cage length. In some cases, there are solutions for longer travels possible with running out of cages.
Cage creep resulting in stroke shortage: In vertical mounting orientation or high dynamic applications the cage may drift from its original position. This is due to the force of gravity. In case of misalignment of poor machine assembly structures the cage also may drift from its center position and can hit the end stops. PM offers a well-proven solution preventing cage drift, available for all types of applications. Click on this link for information about Cage Creep and the robust and reliable solution PM offers.
To meet the demands of various industries and different applications PM offers 3 types of modern cross roller bearing designs. We have written an article about the differences between them. Follow this link to gain more information about this topic.
Below, we would like to briefly give a few sentences to the different types.
Cross roller guide type RSD is the most widely used linear guide and is particularly versatile. It offers low friction and it can accommodate load and moments from all directions. This linear guide offers the most sizes and lengths of linear guides and a broad range of different cage types and materials. Type RSD linear guide can be supplied either with ball cages or cross roller cages. It can handle light up to medium loads.
Click on this link to visit the product page of the cross roller guide type RSD.
Cross roller linear guide type RSDE is designed when higher load carrying capacity is needed, of higher stiffness and precision due to higher speeds. Only available with cross roller cages and actually in 3 sizes (3, 4, and 6 mm). Interchangeable with type RSD cross roller guide. The design features a deeper V-groove combined with a high density of rollers in the cage. Offering 3 times higher load ratings than RSD type and double the stiffness.
Optional available with anti-cage creep (ACC) mechanism.
Click on this link to visit the product page of the high-load cross rolller guide type RSDE.
Cross roller linear guide type RNG combines the advantages of the linear guide type RSDE with a compact design. Available in sizes 4 and 6 mm. Optional available with anti-cage creep (ACC) mechanism.
Click on this link to visit the product page of the compact cross roller guide type RNG.
Click on this link for the article to read more about the differences in cross roller guides, taking a deep dive into the characteristics of cross roller type precision linear guides.
Cross roller guides are the product of choice when precision is required in a machine. The wide range of designs ensures that there is a suitable guide for every application, ranging from light to heavy loads. Mounting the guides requires some knowledge and experience, which is to be expected given the increasing requirements.
The compact mounting dimensions, the addition of modern designs, and the increasing precision of these linear guides ensure that the next generation of machines can be equipped with them. The further development of cross roller linear guides allows machines to become more compact and further increase output.