Linear Bearings.

What are Linear Bearings?

Linear bearings, also known as linear ball bearings, linear ball bushings or linear motion bearings, are rolling-element components built to carry a load smoothly along a shaft rather than rotate around one. Where a rotary bearing turns on a fixed centre, a linear bearing travels the length of a hardened round shaft, converting rolling contact into low-friction sliding motion. 

Physically, linear bearings are compact cylindrical steel sleeves with rows of precision balls held in closed tracks that run along the bore. Those ball tracks let the bushing glide freely in one axis while resisting the play and stiction (a blend of static and friction) that would otherwise creep into a sliding joint. It is this combination of accuracy and low resistance that makes the linear bearing a foundational building block wherever a mechanism has to move in a straight line repeatedly and reliably.

How Linear Bearings Work

A linear bearing works by recirculating its balls through closed loops inside the sleeve. As the bushing moves along the shaft, the loaded balls roll through the contact zone, then lift away and circulate back around to re-enter the track, so the same few balls carry the load in turn as travel continues. Only a small number bear load at any instant, which keeps friction low and motion consistent across the full stroke. The shaft itself does the guiding, so the hardened surface finish and the fit between bore and shaft govern how precise and how quiet the movement is.

Take the X-axis carriage of a desktop CNC router as a working example. Two linear ball bearings ride on each hardened ground shaft, with the cutting head mounted to the carriage between them. As the stepper drives the carriage back and forth, the bushings keep the head travelling straight and true against the sideways cutting forces, so the tool tracks the intended path rather than wandering. Swap in the sealed variant and the same assembly shrugs off the dust and swarf thrown up by machining, protecting the raceways and extending service life. The engineer gets repeatable positioning, low drag on the motor and a linear slide bearing that keeps performing in a dirty working environment.

Materials Linear Bearings Are Made From

Accu’s range of linear bearings is manufactured from proven bearing-grade materials chosen for load capacity, wear resistance and long service life under repeated motion. 

• Steel - (AISI 52100): A high-carbon chromium bearing steel, hardened for a tough, low-wear raceway that keeps the sleeve and balls accurate under constant back-and-forth travel.
• Rubber - Buna (sealed variants): Nitrile rubber wiper seals on the UU variant hold the grease charge and wipe swarf and moisture off the shaft, at a slight cost in drag.

Sizes and Types of Linear Bearings Available

Accu's linear bearings span the LM series from LM4 to LM20, covering ten bore sizes to suit shaft diameters across small and mid-scale mechanisms. 

• Inside diameters: from 4 mm to 20 mm 
• Outside diameters: from 8 mm to 32 mm 
• Overall lengths: from 12 mm to 42 mm

Our linear ball bearings are held to tight tolerances, with bore tolerances as fine as 0 to -0.008 mm on the smallest sizes, tightening the fit between bearing and shaft where positioning accuracy matters most. The parts are supplied in their natural bearing-steel finish, with no additional coating or plating applied.

Four linear bearing closure types cover the majority of engineering applications: 

• Standard bushing: open at both ends for maximum speed and the highest dynamic load rating.
• Double Seal (UU) variant: carries rubber seals at both ends to retain grease and keep contamination out.
• Adjustable type: features a radial slot that lets the internal clearance be tuned to the shaft on fitting, which is useful for dialling out play in a specific installation. 
• Open type: has a longitudinal cut-away so the bushing can run over shaft supports, allowing it to work as a linear rail bearing on a fully supported shaft where the rail is fixed along its whole length rather than only at its ends. 

FAQs

Q: What is the 2:1 rule for linear bearings?

A: The 2:1 rule, sometimes called the 2:1 binding ratio, is a design guideline for avoiding binding in linear motion systems. It holds that the distance between the driving force and the supporting bearing should not exceed roughly twice the bearing's effective bearing length or twice the spacing between two bushings sharing a shaft. 

Push past that ratio and the reaction forces on the bushing climb steeply, so the carriage tends to judder or seize rather than slide freely. Keeping the overhang within the 2:1 limit or spreading the load across two bearings set an adequate distance apart keeps travel smooth. 

Q: Is grease or oil better for linear bearings?

A: It depends on the duty. Grease is the default for most linear ball bearings because it clings to the raceways, needs relubricating far less often and, in the sealed (UU) variants, is held in place by the rubber seals while contamination is kept out.

Oil comes into its own where speeds or temperatures are high enough that heat requires dissipating or where a circulating oil supply is already part of the machine, but it drains more readily and calls for better sealing and more frequent attention. 

For typical shaft-guided applications, grease is usually the more practical choice.

Q: How do you identify a linear bearing?

A: A linear bearing is built to slide along a shaft rather than turn around one, so the giveaway is the internal construction: rows of balls running in closed, axial recirculating tracks along the bore, in contrast to the single circular race of a rotary bearing.

Bespoke Linear Bearings Manufacture.

High precision, bespoke manufacture of Linear Bearings to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.