A locating and floating bearing arrangement uses one bearing position to establish the shaft’s axial reference and another to accommodate relative axial movement. It is often appropriate where a shaft and housing will experience different temperature changes, but it only works if the bearing geometry, fits, shoulders, retainers, and assembly sequence preserve the intended freedom of movement.
Define which bearing position locates the shaft
In a conventional locating–floating arrangement, both bearing positions support radial load. Only the locating position is intended to establish the shaft’s axial position relative to the housing. The locating bearing must therefore react the applicable axial load and hold the shaft-mounted components that require a stable axial datum.
That datum may be important for a gear mesh, pump impeller clearance, mechanical seal position, coupling spacing, rotor position, or another component whose axial movement is limited by the machine design. Start with the assembly drawing rather than selecting the locating side from bearing type alone.
A locating position normally has positive axial retention for the bearing rings that must transmit thrust. Depending on the design, this can include shaft shoulders, locknuts, spacers, housing shoulders, end covers, retaining rings, or clamping plates. The relevant issue is not merely whether a ring is retained; it is whether there is a continuous load path from the shaft-mounted thrust source, through the bearing, into the housing structure for each expected thrust direction.
Fixed–free arrangements are commonly used where axial guidance requirements are moderate and thermal displacement must be accommodated. However, they are not the only arrangement. Preloaded or adjusted bearing pairs, cross-located arrangements, and fully floating arrangements may be more suitable where the machine requires high axial stiffness, controlled endplay, precise rotor position, or bidirectional thrust capacity. NTN’s overview of fixed, floating, and adjusted bearing arrangements is useful background, but the exact arrangement must be checked against the selected bearing manufacturer’s documentation and the machine duty.
Before assigning the locating side, collect these inputs:
- The component that requires an axial reference and its permissible axial movement.
- Radial and axial loads, including load direction, reversals, start-up events, and fault conditions.
- Shaft speed, expected vibration, lubrication method, contamination exposure, and misalignment.
- Bearing-center distance and the shaft and housing temperature profile in service.
- Available shoulders, covers, locknuts, seal locations, and assembly access at each support.
Do not select the floating side simply because that bearing carries the lower radial load. Lower drag can be helpful where a ring must slide, but temperature distribution, thrust path, bearing design, ring creep risk, sealing, and installation constraints can change the appropriate choice.
Calculate the axial movement the floating position must accommodate
The floating position is intended to prevent thermal growth and dimensional variation from creating unintended axial preload or excessive internal stress in the bearing system. The relevant quantity is relative axial displacement between the shaft-bearing system and the housing-bearing system, not shaft expansion considered in isolation.
For a preliminary thermal calculation, axial expansion can be estimated as:
[ \Delta L = \alpha \times L \times \Delta T ]
where:
- (\Delta L) is axial length change;
- (\alpha) is the coefficient of thermal expansion for the actual material;
- (L) is the effective length between the relevant reference points; and
- (\Delta T) is the temperature change from the assembly reference condition.
In a bearing arrangement, calculate the shaft growth and housing growth over their respective effective distances, then consider the difference. A steel shaft and a cast-iron or aluminum housing may expand by different amounts even if their temperatures rise by the same number of degrees. In many machines, their operating temperatures are not the same either. A shaft heated by process fluid, rotor losses, or a hot coupling may run appreciably hotter than a housing exposed to ambient air or cooling flow.
The calculated thermal displacement is only one part of the required float. Add or review the axial tolerance stack-up from shaft shoulders, housing shoulders, covers, bearing widths, spacers, seal carriers, and other locating features. Manufacturing variation can consume available movement even before the machine reaches operating temperature.
The final displacement allowance must also be compatible with connected equipment. For example, a gear mesh, seal face arrangement, coupling, or driven element may impose a limit on acceptable shaft movement. If the permissible movement of one component is smaller than the thermal movement calculated for the bearing span, the solution may require a different shaft layout, different thermal control, an adjusted bearing arrangement, or a review by the equipment designer.
Use credible temperatures. Measured operating temperatures, validated thermal analysis, or documented duty data are preferable to a generic temperature assumption. Do not assign a movement value from a rule of thumb without stating the bearing spacing, material properties, assembly temperature, and expected operating temperature range.
Choose how the non-locating position will float
A non-locating bearing position can accommodate axial displacement in several ways. The correct method depends on the exact bearing design and series, the applied load, speed, lubrication, required fit, and manufacturer mounting instructions.
Internal displacement within the bearing design
Some bearing designs can accommodate relative axial movement internally between the rings while continuing to carry radial load. Certain cylindrical roller bearing configurations are commonly used this way, but this is not a property that should be assumed from the broad bearing family name. The exact ring design, flange arrangement, cage, clearance, and manufacturer’s stated capability matter.
Where internal displacement is used, both bearing rings can generally be held with fits appropriate to their load conditions because the axial movement occurs inside the bearing. Confirm the permissible displacement and any restrictions on axial load, speed, lubrication, or operating clearance in the catalog for the exact bearing designation.
A bearing ring sliding on the shaft
A floating position can also be created by allowing one ring to slide axially on its seat. This approach requires enough axial clearance and a surface condition suitable for controlled movement. It also requires careful consideration of ring creep: a ring subject to rotating load is often more likely to require an interference fit, while a sliding fit may be necessary for the intended axial movement.
This apparent conflict is why fit selection cannot be copied from a generic table without reviewing the actual load direction and rotating-ring condition. If the design expects the inner ring to slide on the shaft, confirm that the manufacturer permits that arrangement and specify the shaft diameter, roundness, cylindricity, surface finish, hardness where applicable, and lubrication or corrosion protection for the interface.
A bearing ring sliding in the housing
Alternatively, the outer ring may slide axially in the housing bore. This is common where the inner ring requires a secure shaft fit but the housing geometry can provide a controlled sliding seat. The bore tolerance, material, surface finish, temperature, and likelihood of corrosion or fretting all affect whether the ring will move as intended.
Do not confuse intentional axial sliding with a loose or poorly controlled housing fit. The ring still needs adequate radial support and must not spin or creep in a manner that damages the housing. Confirm the arrangement in the bearing manufacturer’s mounting documentation for the exact product and duty.
Specify fits and retention without blocking movement
The most frequent arrangement error is to describe one bearing as “floating” while trapping both rings axially with shoulders, end covers, locknuts, spacers, or retaining rings. If the selected bearing does not provide internal axial displacement, that installation has converted the nominal floating support into a second locating support.
Review the floating bearing position on a section drawing. For each ring, ask three questions:
- Is this ring intended to be axially fixed or permitted to move?
- If it is permitted to move, what feature provides the available travel?
- Can any cover, seal carrier, spacer, locknut, or retaining feature contact the ring and remove that travel during assembly or operation?
The locating position needs positive retention in the thrust direction or directions that it must carry. The floating position needs one clearly defined axial freedom unless the bearing itself provides the required internal displacement. A cover that is harmless in one arrangement can become an unintended clamp in another.
Fits must be selected using the bearing manufacturer’s tables for the actual bearing type, size, tolerance class, load magnitude, load direction, rotating-ring condition, temperature, and housing material. Interference may be needed to prevent creep under a rotating load, but excessive interference can reduce internal clearance or create damaging stresses. Clearance fits may permit float, but can be unsuitable where radial load or vibration would cause ring movement and fretting.
Also check geometric and mounting details that are easily missed in a nominal-diameter fit callout:
- Shaft-seat and housing-bore roundness and cylindricity.
- Shoulder height and support face perpendicularity.
- Fillet radii relative to the bearing chamfer.
- Spacer parallelism and burr-free contact faces.
- End-cover flatness and bolt tightening sequence.
- Compatibility of mounting tools with the ring receiving the installation force.
Apply mounting force only to the ring being fitted. Pressing through rolling elements can damage raceways and rolling contacts. For heated mounting, use the bearing manufacturer’s permitted heating method and temperature limit; do not use uncontrolled flame heating.
Check axial load paths and reversed-thrust conditions
A locating bearing arrangement is only valid if it can react all applicable thrust loads. Develop a free-body diagram showing the source, direction, magnitude, and duration of axial loads. Include normal operation, start-up, shutdown, pressure changes, gear forces, helical gear thrust, screw or pump thrust, belt or coupling effects, and credible abnormal events.
A single locating bearing may be suitable when thrust is modest and the chosen bearing is rated and mounted to carry it in the required direction. It may not be sufficient where thrust reverses frequently, where the shaft position must be tightly controlled, or where preload and axial stiffness are functional requirements.
For example, a paired angular-contact or tapered roller bearing arrangement may be selected where bidirectional thrust, controlled endplay, or preload is required. Such arrangements introduce their own requirements for orientation, spacer accuracy, preload setting, thermal behavior, and tightening procedure. They should not be substituted for a locating–floating arrangement without reviewing the whole shaft system.
Likewise, a deep-groove ball bearing can be used as a locating bearing in some machines because it can support combined radial and axial loading within its documented limits. It can also be part of a locating–floating system if the other position provides the required axial freedom. Whether it is suitable depends on the exact bearing’s axial capacity, clearance class, fits, speed, lubrication, and thrust duty—not on the label “deep-groove” alone.
Verify the arrangement during installation and commissioning
Installation verification should demonstrate that the manufactured assembly matches the intended degrees of freedom. Do not rely on a general arrangement description after components are installed.
Before mounting, review the released assembly drawing, bill of materials, bearing orientation details, and manufacturer instructions. Identify the locating side, the floating side, the ring intended to move or the bearing feature that provides internal displacement, and the specified displacement allowance.
A practical inspection sequence is:
- Confirm the bearing part numbers, suffixes, orientation, and applicable clearance or preload specification.
- Measure or verify shaft-seat and housing-bore dimensions against the released fit requirements.
- Inspect shoulders, radii, spacers, covers, and retainers for burrs, damage, or geometry that prevents full ring seating.
- Mount each bearing with the correct tool contact and approved heating or pressing procedure.
- At the locating position, verify that the specified rings are fully seated against their intended reference faces.
- At the floating position, verify the specified travel or residual displacement allowance where the design and manufacturer procedure permit this measurement.
- Check that seals, covers, locknuts, circlips, and fasteners do not introduce an unintended axial clamp.
- Record dimensions, axial-clearance or travel observations, torque values where specified, and any deviations from the assembly procedure.
Do not manually force a bearing to slide after final assembly merely to prove that it floats. Seals, preload devices, locking features, lubrication state, or manufacturer instructions may prohibit that action. Use the approved measurement method for the machine.
During commissioning, follow the machine-specific safety procedure for lockout/tagout, electrical isolation, pressure isolation, guards, and rotating-equipment hazards. Observe only the condition-monitoring limits and acceptance criteria specified for the equipment. Unexpected temperature rise, noise, vibration, or axial movement should trigger an engineering review rather than an assumption that the floating bearing is functioning correctly.
Common questions
Can both bearings locate a shaft?
Yes, but that is not a conventional locating–floating arrangement. Two axially locating supports may be used in adjusted, preloaded, or otherwise application-specific arrangements. The design must account for thermal expansion, preload variation, tolerance stack-up, and axial stiffness. Treating both supports as fixed without that analysis can create unwanted bearing load as temperatures change.
Which bearing ring should be allowed to slide in a floating position?
Either ring may be the moving ring, or the bearing may accommodate movement internally, depending on the bearing design and duty. Choose the method from the exact bearing manufacturer guidance after reviewing rotating-ring load, creep risk, required fit, housing and shaft materials, temperature, and available retention geometry.
How much axial movement should a floating bearing allow?
It should accommodate the calculated relative thermal displacement plus the relevant tolerance stack-up, while remaining within the permitted movement of connected components and the bearing manufacturer’s limits. There is no universal travel value.
Can a deep-groove ball bearing be used in a locating and floating arrangement?
It can be used in some arrangements, provided its load capability and mounting arrangement suit the duty. A deep-groove ball bearing used at the locating position must be able to carry the applicable thrust load. If used at the non-locating position, the installation still needs a deliberate means of allowing axial displacement.
The selection rule is simple but demanding in execution: establish one defined axial reference where the machine needs it, calculate the relative movement that must be absorbed elsewhere, and verify on the completed drawing that no fit or retaining feature defeats that intended freedom. When thrust loading, preload, temperature distribution, or allowable shaft movement is uncertain, the bearing and machine manufacturers should review the arrangement before release.
