The Art of Bearing Arrangements: A Guide to Locating-Non-locating and Paired Mounting

The Classic Arrangement: Locating / Non-locating (Fixed / Floating)

This is the most common and reliable arrangement in industrial design. It cleverly solves a fundamental conflict: precise positioning versus thermal expansion.

The Principle

When a shaft heats up during operation, it gets longer. If both ends were locked in place, immense thermal stress would build up and destroy the bearings. The locating-non-locating arrangement solves this perfectly:

• Locating end (Fixed end): This end locates the shaft axially in both directions and also supports the radial load. It acts like an “anchor,” holding the shaft firmly in one position.
• Non-locating end (Floating end): This end only supports the radial load and is “free” to move in the axial direction. It allows the shaft to expand or contract freely, acting like a support on a sliding rail.

Common Combinations for the Locating End

• A single deep groove ball bearing: Can handle moderate axial loads in both directions. Simple and cost-effective.
• A pair of angular contact ball bearings or tapered roller bearings: Mounted back-to-back, they provide very high positioning accuracy and rigidity.

Common Combinations for the Non-locating End

• An N or NU type cylindrical roller bearing: Its inner and outer rings can move axially relative to each other, making it an ideal floating bearing.
• A deep groove ball bearing: By using a sliding fit between its outer ring and the housing bore, it can be allowed to float axially.

High-Rigidity Arrangements: Paired Mounting

For demanding applications like machine tool spindles or high-precision gearboxes, we need more than just shaft location. We need the entire system to have extremely high rigidity (the ability to resist deformation). This requires mounting two angular contact ball bearings or tapered roller bearings as a “pair.”

Back-to-Back (DB, ‘O’ Arrangement)

• Structure: The wide faces of the two bearings are facing away from each other. The lines of pressure form an “O” shape, creating a wide and stable support base.
• Characteristics: This is the most rigid arrangement. It is extremely effective at handling moment loads (forces that try to tilt the shaft). It is the top choice for machine tool spindles.

Face-to-Face (DF, ‘X’ Arrangement)

• Structure: The narrow faces of the two bearings are facing each other. The lines of pressure form an “X” shape, resulting in a narrower support base.
• Characteristics: Rigidity is slightly lower than the DB arrangement, but it is less sensitive to misalignment during assembly, making it easier to install.

Tandem (DT)

• Structure: The two bearings are mounted next to each other, facing the same direction.
• Characteristics: This arrangement cannot provide axial location in both directions. Its sole purpose is to have two bearings share a very heavy axial load coming from a single direction.

Checklist for Choosing an Arrangement

Before deciding which arrangement to use, ask yourself these questions:

1. Will my equipment have significant temperature changes and thermal expansion?

• → If yes, a locating-non-locating arrangement is essential.

2. Does my shaft need to resist strong tilting or moment loads?

• → If yes, the back-to-back (DB) paired mounting is the best choice.

3. Do I have extremely high requirements for system rigidity?

• → If yes, choose a paired mounting arrangement (DB or DF).

4. Is there a very heavy axial load from one direction that a single bearing cannot handle?

• → If yes, consider the tandem (DT) arrangement.

Conclusion

A bearing arrangement is not just a simple assembly of parts; it is an art of balance. A suitable arrangement is the absolute foundation for unlocking the full performance of your bearings and ensuring the long-term stability and precision of your entire mechanical system. Whether you choose a locating-non-locating or a paired mounting setup depends on your combined requirements for precision, rigidity, and cost.