Bearing Arrangements: Types, Back-to-Back vs Face-to-Face, Tandem and Where Each Is Used
Bearings are critical components in many machines, providing rotational or linear motion while reducing friction and handling stress. Super precision bearings are essential for high-performance applications where accuracy, speed, and rigidity are paramount. Understanding the various bearing arrangements and their suitability for specific conditions is key to choosing the right solution with confidence and peace of mind.
It's important to remember that assessing the operating environment of your bearings is essential to understanding the different arrangements that are required for your machinery to work at its best.
Assessing the Operating Environment
Let’s look at how to assess your operating environment and application needs:
- Operating environment: Bearings might be exposed to contaminants such as dust, moisture, or chemicals. To prevent premature wear and failure, selecting a bearing arrangement that incorporates effective seals or lubrication is essential in such conditions.
- Maximum operating speed: Bearings must withstand the rotational speed demanded by the application. High-speed operations require bearings with low friction, precise geometry, and stable materials to maintain performance.
- Operating temperature: Applications involving significant heat or temperature fluctuations demand bearings designed for thermal stability. Improper handling of temperature variations can lead to wear or loss of precision.
- Rigidity requirements: For applications needing enhanced stiffness, such as in machining or robotics, specific bearing arrangements provide increased rigidity to minimise deflection and improve accuracy.
- Load combinations: Understanding the effect the applied load has on the bearing arrangement will help with the selection process and, crucially, will help define which arrangement is required in the correct orientation to the applied load.
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Types of Super Precision Bearing Arrangements
Super precision bearings can be configured in various arrangements to optimise performance for different operating and loading conditions, helping you find the perfect fit for your specific needs. Below are common arrangements and their typical applications:
Universal combination (DU – 2 row)
These bearings are designed to be mounted in pairs and are preloaded for high precision. Universal combinations offer flexibility for:
Back-to-back (DB)
Back-to-back (or DB) arrangements provide high rigidity and resistance to tilting moments and are commonly used in applications requiring stability under heavy radial and axial loads. These arrangements are often found in high-speed turbines and control systems.
Face-to-face (DF)
Face-to-face (or DF) arrangements accommodates slight misalignment better than DB, suitable for applications where space constraints necessitate a more compact design. Scanners and surgical tools often use DF configurations for compact design and alignment flexibility.
Tandem (DT)
Tandem (or DT) arrangements handle higher axial loads in one direction by distributing the load across two bearings. These arrangements are commonly found in aerospace applications such as high-speed turbines and control systems. They are also found in robotics due to the stiffness and load-handling capabilities.
Universal combination (DUD – 3 rows)
DBD
DBD arrangements improve handling of combined loads and moments, often used in live centres of spindles in precision grinding machines and other high-rigidity applications for rigidity and load management.
DFD
DFD arrangements offer better alignment flexibility than DBD while maintaining load capacity, often found in ball screw supports.
DTD
DTD 3 row arrangements provide even greater axial load capacity, particularly in one direction. They are suitable for application like high-speed turbines and axial compressors, they are also common in robotics due to the stiffness and load-handling capabilities.
Universal combination (QU – 4 rows)
DBB
A DBB arrangement ensures maximum rigidity and resistance to angular deflection, this makes it ideal for CNC machining centres where precision and stability are critical. CNC machining centres and grinders also utilise DBB arrangements for rigidity and load management.
DFF
Provide good axial and radial load capacity with some flexibility for misalignment.
DTT
Designed for extremely high axial loads in one direction, DTT arrangements are often found in axial compressors and turbines for their superior load capabilities and thermal stability.
DBT
DBT offer a balance of axial and radial load handling with flexibility for directional force distribution.
DFT
DFT blend alignments tolerance with enhanced axial load capacity and are often found in axial compressors and turbines for their superior load capabilities and thermal stability.
Choosing the Right Bearing Arrangement
Selecting the optimal bearing arrangement involves analysing load requirements, assessing environmental factors, and prioritising application goals. By understanding these factors, you can ensure the chosen super precision bearing arrangement meets the specific demands of your application, providing reliable performance and extending the bearing’s service life.
With the right choice, you’ll achieve lasting performance and peace of mind. Talk to our product experts for help selecting the best options for your machinery or order your arrangements from our website.
Bearing arrangement FAQs
What does DU, DG or "universally matchable" mean?
These codes identify bearings made for universal matching.
SKF uses DG for a universally matchable pair, with TG and QG for sets of three and four. FAG, GMN and IBC use DU, TU and QU, while NSK uses DU, DUD and QU (SKF interchange guide). SKF defines universally matchable bearings as those made so that, mounted in random order immediately adjacent to each other, they reach a given preload or even load distribution without shims.
Can I pair two standard angular contact bearings myself?
Only if both carry the universal matching marker, the G in SKF designations such as 7016 CDGB/P4A. Without it, there is no guarantee the two bearings will share load evenly or reach the intended preload, so buy a matched set or universally matchable bearings from the angular contact ball bearing range instead.
How does shaft heat affect preload in back-to-back and face-to-face arrangements?
In most applications, the shaft runs warmer than the housing. NSK explains that a face-to-face pair then always loses clearance in operation, so its preload rises as it warms.
A back-to-back pair depends on the geometry of its contact cones. If their apexes touch, thermal effects cancel out and clearance stays the same. If they overlap, clearance decreases. If they do not overlap, clearance increases.
Need help specifying a bearing arrangement?
Acorn is the UK's first SKF Super Precision Bearing Partner, with same-day despatch on hundreds of stocked items.
Our Super Precision Bearing Centre supports bearing selection, specification and interchange from standard to super precision designs.
Through our super precision bearing services, we supply anything from a single replacement to a complete matched set configured for your application, and advise on preload selection, bearing arrangements and manufacturer-specific designations when converting between brands.
If you are unsure which arrangement your machine needs, or what an existing designation means, speak to our bearing specialists. Browse our full range of bearings or find your nearest branch.