1. Structure of Linear Bearings
An LM linear bearing is built from a small number of parts, each with a specific job:
| Component | Function |
|---|---|
| Bearing block / outer sleeve | Houses the ball circuits and carries the mounting interface |
| Ball retainer & recirculating balls | Convert sliding friction into rolling friction as the bearing travels |
| Shaft / rod | Precision-ground steel or stainless steel rod that the bearing rides on |
| Flange (optional) | Provides the mounting interface - square, round, or oval |
| Seals / dust wipers | Keep contaminants out and retain lubricant |
| Lubrication ports / felt oilers | Allow grease or oil replenishment without disassembly |
Typical material options:
- Chrome bearing steel (GCr15 / SUJ2) - standard, cost-effective, good wear resistance
- Stainless steel (440C) - for washdown, food-grade, or corrosive environments
- Engineering plastic raceways (POM/Delrin) - for quieter, lubrication-free operation at lighter loads
2. Working Principle of Linear Bearings
Inside the bearing block, rows of balls recirculate in a closed loop. As the block moves, balls on the load-bearing side roll between the shaft and the raceway; at the end of travel they recirculate back through a return channel inside the retainer. This rolling action - rather than direct metal-to-metal sliding - is what gives linear bearings their low friction and long service life.
- Rolling vs. sliding friction: Ball recirculation reduces resistance dramatically compared to a plain sliding bushing, which improves both speed capability and positioning accuracy.
- Load distribution: Multiple ball rows around the shaft circumference distribute radial load evenly. Most LM bearings are designed primarily for radial loads, with only light tolerance for axial (thrust) load.
- Clearance / preload: Closed-type bearings ship with fixed internal clearance. Open-type bearings let you adjust clearance after installation - useful when compensating for shaft tolerance or wear over time.
- Precision grades: Backlash and running accuracy depend on the bearing's tolerance grade - typically offered in standard and high-precision classes by most manufacturers.
3. Types of LM Series Linear Bearings
By mounting style (flanged vs. non-flanged)
| Type | Mounting Method | Relative Load Capacity | Best For |
|---|---|---|---|
| Square Flange | Bolted from the side, 4 corner holes | Medium–High | General-purpose horizontal/vertical mounting; most widely stocked |
| Round Flange | Bolted from the front face, circular pattern | Medium | Compact housings; easy concentric alignment |
| Oval Flange | Bolted from the top, 2 elongated holes | Medium–High | Applications needing a larger bearing contact area |
| Non-Flange (cylindrical) | Press-fit into a custom housing bore | Light–Medium | Space-constrained or custom-housed designs |
| Open Type | Slotted housing, adjustable clearance | Medium | Applications needing preload tuning or easy field maintenance |
By length
- Standard Type: shorter overall length, suited to light-to-medium loads and moderate stroke.
- Long Type: extended length increases the moment-load capacity and rigidity - useful when the load is offset from the shaft centerline.
including square flange, round flange, oval flange and open type
for different mounting requirements.
Need help picking a type? Send us your shaft diameter, load, and mounting space, and we'll recommend the right configuration within 1 business day.
4. How to Choose the Right Linear Bearing
Work through these factors in order:
- Load direction and magnitude - Is the load purely radial, or is there a meaningful axial component? Heavy or combined loads may call for a linear guideway instead (see next section).
- Speed and duty cycle - Continuous high-speed operation needs better sealing and a defined re-lubrication interval; intermittent light use has more flexibility.
- Environment - Dusty, wet, or high-temperature environments favor stainless steel, sealed, or waterproof variants over standard steel/open designs.
- Mounting space and orientation - This usually decides flange shape: square flange for accessible bolt-down surfaces, round flange for tight cylindrical housings, oval flange when you need extra bearing area without going to a larger bore.
- Precision requirement - Tight positioning accuracy (e.g., CNC, optical, metrology equipment) calls for a high-precision grade bearing and a ground/hardened shaft.
- Maintenance access - If preload will need periodic adjustment, an open-type bearing saves significant downtime versus a closed type.
- Shaft support method - Fully supported shafts (supported on their full length) allow longer unsupported spans than shaft ends only; this affects how many bearings and supports you need per axis.
5. Linear Bearing vs. Linear Guideway: What's the Difference?
A common question from engineers new to linear motion: should I use a round-shaft linear bearing or a profile linear guideway?
| Feature | Linear Bearing (on round shaft) | Linear Guideway (profile rail) |
|---|---|---|
| Load capacity | Lower, mainly radial | Higher, multi-directional (radial + lateral + moment) |
| Rigidity | Lower | Significantly higher |
| Achievable precision | Good | Excellent |
| Cost | Lower | Higher |
| Installation complexity | Simple - round shaft + supports | More demanding - rail flatness/parallelism critical |
| Typical use case | 3D printers, light automation, packaging, fitness equipment | CNC machine axes, heavy or high-precision positioning systems |
Rule of thumb: if your application is light-to-medium load with moderate precision needs, a linear bearing is usually the more economical choice. If you need high rigidity, multi-directional load capacity, or top-tier repeatability - e.g., on a CNC milling axis - a linear guideway is generally the better fit.
6. Applications of Linear Bearings
- CNC machines and milling equipment - guiding tool heads or workpiece tables for accurate, repeatable machining.
- 3D printers - supporting print heads or beds along X/Y/Z axes to reduce layer shift and print error.
- Aluminum extrusion rail systems - a standard linear-guidance solution in modular automation frames and conveyors.
- Fitness equipment - e.g., Smith machines, where precision bearings provide smooth, low-friction resistance travel.
- Automation and robotics - pick-and-place units, inspection systems, and positioning tables that need low-friction, repeatable linear motion.
7. Frequently Asked Questions
Is a "linear bearing" the same thing as a "ball bushing"?
Yes - these terms are generally used interchangeably for the round-shaft, ball-recirculating bearing type covered in this guide.
What is the typical service life of a linear bearing?
Service life depends primarily on load, speed, contamination, and lubrication interval. With correct sealing and a regular re-lubrication schedule, LM bearings can run reliably for years in industrial duty cycles; harsh or unlubricated conditions will shorten that significantly.
Can a linear bearing handle axial (thrust) loads?
LM bearings are designed mainly for radial load and can tolerate only light, incidental axial load. For applications with significant axial loading, pair the bearing with a separate thrust element, or consider a linear guideway/ball screw combination instead.
Open type vs. closed type - which should I choose?
Choose open type if you anticipate needing to adjust preload or inspect/clean the bearing in the field without removing the shaft. Choose closed type for simpler, maintenance-light installations where factory-set clearance is sufficient.
How important is shaft alignment when using multiple linear bearings on one axis?
Very important. Misaligned or non-parallel shafts cause uneven load distribution, premature wear, and increased running friction - always check shaft straightness and parallelism (especially on multi-bearing, multi-shaft axes) during installation.
Linear bearing or linear guideway for my CNC project?
For light-duty or hobby CNC, a linear bearing on a supported round shaft is usually sufficient and more cost-effective. For production CNC machines needing high rigidity and long-term accuracy under cutting loads, a linear guideway is the standard choice.
8. Conclusion
LM Series Linear Bearings remain the go-to solution for light- to medium-load linear motion on round shafts. Choosing the right configuration comes down to four decisions: flange type (square, round, oval, or non-flange), clearance type (closed or open), material (steel, stainless, or plastic-lined), and length (standard or long).
Key takeaways:
- Linear bearings convert sliding friction into rolling friction via recirculating balls, enabling smooth, low-friction, repeatable motion.
- Four main flange configurations cover most mounting scenarios - match flange shape to your available mounting space and required load capacity.
- For loads or precision beyond what a round-shaft bearing can deliver, a linear guideway is the better choice.
- Proper shaft alignment and lubrication interval are the two biggest factors in long-term bearing life.
Not sure which configuration fits your project? Contact our engineering team → - send your shaft diameter, load, speed, and environment, and we'll recommend a configuration with pricing.
