Needle roller linear guideways are offered in two highly compact designs: type N/O and type M/V. These types of linear guides are used in high-load applications with limited stroke. They support and guide high loads and high moments with great precision. The non-recirculating bearing design results in ultra-smooth linear motion.
Frictionless linear guideways for limited stroke length are also called precision rail guides or linear bearings. In general, they are equipped with cages which retain the rolling elements. It is possible to mount end pieces at both rail ends to prevent the cage from running out.
Linear guides are fitted with either ball cages (precision ball linear guides), cylindrical rollers in a crossed arrangement, also called crossed-roller cages (or crossed-roller linear guides), or needle rollers cages (also called needle roller linear guides). The stroke length is defined as twice the difference in length between the guideways and the cage.
The different types of linear bearings have different load-carrying characteristics and rigidity. Crossed-roller linear guides offer “next level” performance of ball linear guides, especially in terms of load capacity and rigidity. Equally outstanding are the needle roller linear guideways, which offer the “next level” in performance of cross-roller linear precision guides.
With the stiffness of a linear guide, we mean the amount of linear guideway deformation under load. As the length of needle rollers is at least 2.4 times their diameter, they offer a larger contact area than cylindrical rollers, with have a diameter-to-length ratio of less than 1. The diameter of needle rollers is smaller compared to cylindrical rollers. As a result, more needle rollers fit in a cage is much more.
Since needles require less space, more needle rollers are needed in a cage to distribute the load. Another main difference between cylindrical rollers and needle rollers is the smaller diameter of needle rollers: the number of rows in a cage can be doubled, resulting in a larger contact area.
A smaller diameter of a rolling element also increases the stiffness of a linear bearing. Less load per needle roller means less deformation and therefore, higher rigidity -potentially- about 50% higher than cross-roller guides RSDE with an equal cage length.
Compared to other linear guides for limited stroke length, the needle roller linear guides provide the following advantages:
Compact size - High load-carry capacity: Since the rolling elements are compact they need less space. Needle rollers have a long contact length with the guideway. Furthermore, a cage holds more needle rollers. As a result, needle roller linear guides can carry higher loads as ball and cross-roller guides with similar dimensions.
High Stiffness - High rigidity: Because needle rollers are smaller in diameter, linear guides contain more of them. Also, the linear guides enable longer contact length between the needle roller and guideway. As a result, they offer higher stiffness and rigidity than ball and cross roller cage linear bearings.
Smooth and accurate movement: All the elements are of the highest quality grade and boast extreme accuracy. The needle roller cage helps to reduce the friction resistance, which is a bit higher than ball and crossed-roller linear bearings.
Interchangeable: Some of the needle roller linear guideways are interchangeable in size with the ball and cross-roller linear guides type RSD and RSDE. This makes them a good alternative in existing applications, where higher load ratings or higher stiffness is required without changing the available space requirements.
Linear bearings for limited stroke lengths are equipped with cages that retain the rolling elements.
The main purposes of a cage are:
Needle roller cages are available in two types: aluminium cages type HW and plastic cages type FF-ZW type.
Cage type HW is made from aluminium, whereas steel and brass are optional. These types of cages are designed for use in extreme conditions. They are also well-equipped for high accelerations. We offer cage type HW with a flat double row cage, bent in a 90° angle. The permissible operating temperature is -30 to +120 °C.
Plastic cage type FF-ZW is a single element cage with a double row of needle rollers, suitable for easy to normal operating conditions. The material of the cage is durable plastic. Greater lengths can easily be created to connect individual elements, using a "snap in" technique with dovetail grooves on both ends of the cage. The permissible operating temperature of the cage is -30 to +80 °C.
One set of needle roller linear guides includes 2 pairs of guides. One set consists of four guideways, two cages and eight end pieces. In this video, all parts are mentioned, and it is visually explained how they operate.
PM delivers the linear guides with a corrosion protective oil film that has to be removed before installation. After installation and during service intervals, the linear guides need to be lubricated. This is vital to create and maintain an oil film between the needle rollers and guideways. This film will reduce friction, protect from corrosion, and extend the operational life. The lubrication can be applied between the pair of guideways, and a tiny amount of oil or grease is sufficient.
It is important to realise that there is less space available for the lubricant, due to the smaller diameter of the needle rollers compared to balls or cylindrical rollers. We recommend regular inspection of the lubrication condition to prevent dry running operation.
At a glance, the needle roller guideways type N/O and M/V look similar. However, if you look more closely, you will see a number of differences. This is because of the origin of the guides. Size N/O-62015 and N/O-92025 are interchangeable with the cross-roller guide sizes 6 and 9 mm.
Type M/V guides are not interchangeable, since their dimensions are not identical. Type N/O has countersunk holes with thread for mounting, while type M/V offers countersunk holes without thread. Optional type M/V guides are provided with an adjusting gib (guideway type ML) to apply an evenly preload force on the guides, instead of using laterally placed set screws.
Needle roller linear bearings offer higher stiffness and higher load-carry capacity than crossed roller linear bearings. As a result, they are commonly used in machine tools, such as grinding machines, EDM machines, measurement machines and medical applications, such as patient beds.