Linear bearings are a type of free motion enabling assemblage that operates in a single dimension. They are used in a wide variety of applications. Most linear bearings need to use a precision shafting and a lubrication system to run efficiently. There are both motorized and non-motorized versions of the linear bearings. There are two main sub-categories of linear bearings:

Rolling Element Slide – Rolling element linear bearings are designed with rolling elements to aid in sliding movement. The movement is achieved with a lower friction that the rolling elements, which can be ball bearings or a roller type of bearing, made possible. The bearings are built into the slide construct, which can be built from a variety of materials such as aluminum, hardened cold rolled steel, galvanized steel, or others as the cage containing the bearings.

Plane Slides – Plane slides are usually designed to have mechanical movement parts that perform the action of moving the slide with a variety of movement technologies. The most common options are those of roller tables, dovetail slides, and XY tables, which are operated via a drive machine part. There are also non-motorized variations of the plain slides that can be activated via inertia, gravity, or by manual movement by hand or with another tool. These types of bearings need to make use of lubrication sources to ensure smooth movement with minimal friction.

Construction of a Rolling Element Linear Bearing

Rolling element slides have a sleeve-like design with built in cages containing ball bearings that have contact with the material being slid across. This design allows the machinery to be efficient by exhibiting smooth motion, low friction, high rigidity, and a longer life span than other types of bearings. The low cost to produce makes them simple to replace or maintain, thus making them an economical choice.

Typical construction of a rolling element linear bearing includes:

A hardened steel or stainless steel shafting that is used for the raceways to prevent corrosion and damage from use as well as contact with materials that may get on the raceways.

Sealants designed to protect the steel to ensure that contamination does not occur or the steel can be cleaned or remedied quickly.

Lubrication is necessary for the rolling elements in order to ensure smooth motion on the tracks. High quality lubricants that last longer are used for the rolling elements’ intended purpose. Lubricant efficiency generally depends on a wide range of variables.

Rolling element bearings are necessary to allow better linear bearing motion.

Ball bearing slides – They are spherical bearings that are housed in a way that allows the rolling element to move on the track.

Roller Slides – Rollers are designed to be fixed on the rolling element or the track and are housed in a way that allows the bearings to move in a single direction.

Linear Ball Bearing Slides

Linear ball bearing slides are also known as “Ball Slides” and are the most common option for linear slides. They are designed to offer precision motion on a single axis. The slides are built to use the bearings in a linear base that often employs self lubrication with carbon or another high efficiency lubricant.

These types of linear bearings have a wide range of uses and are used when manufacturing delicate instruments, robots, cabinetry, and high end appliances. Ball bearing slides have several different uses that can easily make them useful for any application.

Construction of Linear Ball Bearing Linear Slides

Ball bearing linear slides are often composed of materials such as aluminum, hardened cold rolled steel, and galvanized steel. The design is normally a linear row of ball bearings that four rods around the base contain, supporting the carriage for a smoother linear movement. A drive mechanism, inertia or movement by hand, can obtain the linear movement.

Ball bearing linear slides of this type are designed to have a lower weight capacity because they are not as resistant to wear and abrasions as other slide designs. They also need to be able to fit into housing and constructed in a way to work with drive systems that also impairs the total weight capacity.

Linear Roller Slides

Roller slides are a type of non-motorized linear slide. The friction is lower in this type of slide due to the crisscrossed roller bearings that provide heavier load capabilities and allow the power to be applied with inertia or a hand. The crossing of these roller bearings also improves the slide’s control and provides options that are well suited for applications in manufacturing, medicine, and telecommunications. They are able to operate in various conditions whether it is a clean room, vacuum, or material handling and automation machinery environments. This means that they are preferably used in environments with low contaminant levels. They can be combined with separate conveyor systems to reduce load weight and have more rigid movement.

Roller slide bearings are similar to ball bearings. Both are housed within a carriage, but the roller bearings are cylindrical rather than spherical. The rollers are designed to cross at a 90 degree angle and will move within rods that rest on the rollers. The valley shaped bearing race grooves are positioned above and below the carriage and base respectively. The carriage is only permitted to travel as far as the track’s end cap. The carriages are typically designed in aluminum, while the rods and rollers are steel based. The end caps are made from stainless steel.

Roller slides tend to be more expensive than other linear bearings because of the high quality of the components and their accuracy in movement. The roller slides’ multi-axis capabilities ensure greater flexibility in their chosen application. The build materials in roller slides erode much slower due to the fact that the roller bearings have a wider contact surface area when compared to ball bearings that have a contact area of a single point. This consistency throughout the rolling process will have less friction, resulting in less damage to the material.

Linear Plain Bearings

The design for plain bearings is basic and can be compared to rolling element bearings. The main difference is that the bearings slide uses no spherical bearings. The raceways that are used with plain bearings can be built from stainless, hardened, or soft steel or aluminum. The polymer or fluoropolymer that is used with the plain bearings mainly governs this so that an appropriate raceway material hardness is used.

The rigidity of plain bearings is lower than rolling element bearings. They are able to handle contamination well. Seals and scrapers are not required in most applications using the plain bearings. Plain bearings are capable of handling larger temperature ranges than other types of bearings. These bearings may also be constructed from lighter materials such as plastics if the application is appropriate. Plastic plain bearings can withstand oil or lubrication in heavy use environments.

Linear Dovetail Slides

Dovetail slides are a type of rigid linear bearing that is designed with a sliding dovetail joint construction that uses a stationary linear base and carriage. The most common materials used in dovetail slide construction are iron, hard coated aluminum, acetal plastic, or stainless steel. The slide’s carriage has a dovetail shape channel that is designed to lock onto the dovetail shaped base. The dovetail shaped base rail fits snugly into the carriage and allows free movement in both linear directions along the axis. If a platform is fastened to the carriage, a larger weight load can be carried with the resulting dovetail table.

A dovetail slide has a larger surface contact area than other types of linear bearings. Therefore, they require much more force to move the carriage on the rail. It is not uncommon to have slow acceleration with these types of slides. The main problem with dovetails is high friction contact when in use. The dovetail’s main benefit is the fact that it can carry very large loads while remaining low cost and being very durable. Dovetail linear bearings travel long distances with the rails and have higher shock resistance under temporarily unstable conditions.

Chemical, dust, and dirt contaminants are not likely to affect the dovetail bearing. To increase the slide’s power, motorization, and mechanics, electromechanical variations are available for industrialized applications. To motorize or mechanically improve a linear dovetail bearing, use a ball screw apparatus, belts and cables, or other ties that are directly attached to the carriage and motors that hand wheels move. Although the dovetail is better designed for higher load applications, it is not high precision and should be avoided for precision sensitive applications.