Three Types of Rolling Elements
Linear guides differ primarily in the type of rolling or sliding element used:
- Ball guide – point contact, high precision, low starting torque, speeds up to 5 m/s; more sensitive to shocks.
- Roller guide—linear contact, significantly higher load ratings for the same size, typically 2–3 m/s; higher friction, larger design.
- Slide guides—no rolling elements at all; sliding elements made of plastic, bronze, or composite materials; maintenance-free, high damping, corrosion-resistant, but with lower accuracy and typically operating at speeds below 1 m/s.
Three designs
Regardless of the rolling element, the design architecture of the rail and carriage also differs:
| Characteristic | Profile rail | Cage/Flat Guide | Round shaft |
|---|---|---|---|
| Hub | unbegrenzt | limited (≈ 2× cage length) | unbegrenzt |
| Snapshot | All 3 moments | limited | Low (2 shafts required) |
| Smoothness of Operation/Straightness | Very good | highest | gut |
In a profile rail guide, balls or rollers run in ground raceways and are continuously returned to the carriage via return channels (roller recirculation)—the stroke is theoretically unlimited, and the carriage absorbs forces and moments from all directions.
Cage-type and crossed-roller guides operate without recirculation: The rolling elements are housed in a cage between two prismatic raceways and move along with the carriage over half its travel distance. As a result, the stroke is limited to approximately twice the cage length (typically less than 500 mm)—in return, these guides run extremely smoothly, can be preloaded without play, and achieve the highest straightness and repeatability. For long service life, cage offset must be taken into account; high-quality designs address this with cage positive guidance (usually a rack and pinion), which keeps the cage moving at half the carriage speed.
The round shaft guide allows a linear ball bearing to run on a hardened round shaft—either cantilevered (cost-effective, but with limited deflection) or supported (stiffer, for long strokes). It accommodates larger alignment errors but has lower moment stiffness than the profiled rail.
Mnemonic
Briefly applied
A CNC gantry axis with a travel range of several meters requires a profiled rail guide with roller recirculation—only the recirculation of the rolling elements enables this stroke. A coordinate measuring machine with a short travel range that demands the highest straightness, on the other hand, is a classic application for a caged or crossed-roller guide. And a packaging machine in a humid environment that requires minimal maintenance is best served by a slideway guide.
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