How to Choose a Locating and Floating Bearing Arrangement

A locating and floating bearing arrangement places the shaft axially at one support while allowing controlled axial movement at the other. Use it when temperature change, manufacturing tolerance, or housing-to-shaft expansion could change the distance between two bearing seats. The essential design check is not simply whether one bearing is called “floating,” but whether the complete shaft, bearing, seat, housing, and retention system leaves exactly one intended axial movement path.

Define which support locates the shaft

In a locating/non-locating arrangement, the locating support establishes the shaft’s axial position relative to the housing. It normally carries radial load and the applicable axial load. The non-locating support primarily carries radial load while accommodating the axial displacement needed as the distance between the supports changes.

SKF describes this arrangement as one in which the locating support provides axial shaft location and the non-locating support compensates for thermal expansion and accumulated component tolerances between bearings. SKF’s arrangement guidance also makes an important point for selection: the arrangement is a support-system function, not a label that can be assigned to two bearing catalog numbers without reviewing the surrounding parts.

For the locating bearing, both the inner ring and outer ring require defined axial retention. A shaft shoulder and locknut, spacer, clamping sleeve, or end plate may restrain the inner ring. A housing shoulder and end cover may restrain the outer ring. The actual retention method must suit the bearing type, fit, speed, load, and assembly method.

At the non-locating support, one axial movement path must remain available. Depending on the bearing design, this movement occurs either internally between bearing components or by one ring moving axially on its seat. The support is not necessarily free in every direction, and it is not safe to assume it can accept all axial load conditions merely because it is designated non-locating.

This arrangement differs from an adjusted bearing arrangement. In an adjusted arrangement, two bearings are commonly set with clearance, endplay, or preload and jointly guide the shaft axially. That can be appropriate where accurate axial guidance or stiffness is required, but it requires controlled adjustment and is not a substitute for allowing thermal expansion in a long or thermally uneven shaft system.

Calculate the axial movement the floating support must accommodate

Before choosing bearing types or fits, calculate the possible change in distance between the bearing seats. The starting estimate for uniform thermal growth is:

[ \Delta L = \alpha \times L \times \Delta T ]

Where:

• (\Delta L) is the change in length.
• (\alpha) is the coefficient of linear thermal expansion for the material.
• (L) is the relevant distance between support reference points.
• (\Delta T) is the temperature change from the assembly or reference condition.

The calculation is only a starting point. In a real machine, the shaft and housing may use different materials, operate at different temperatures, and have temperature gradients along their length. A steel shaft inside an aluminium housing, for example, requires a different assessment from a steel shaft in a cast-iron housing. The relevant movement is the relative change in bearing-seat spacing, not simply the shaft’s absolute growth.

Schaeffler notes that manufacturing tolerances and operating temperature increases can change the relationship between shaft and housing bearing-seat distances, with the non-locating bearing compensating for those differences. Its technical principles guide distinguishes locating/non-locating arrangements from other shaft-support concepts for this reason.

Collect these inputs before specifying available travel:

• Bearing centre distance and the axial reference faces used on the drawing.
• Shaft, housing, and carrier materials.
• Assembly temperature and expected operating temperatures at both supports.
• Expected temperature gradients, start-stop cycles, and transient heating.
• Tolerances on shaft shoulders, housing shoulders, spacers, end covers, and bearing widths.
• Axial displacement already consumed by assembly clearances or adjustment features.
• Manufacturer limits for the proposed bearing design and mounting arrangement.

The permitted travel should exceed the calculated relative movement after considering tolerance stack-up. Do not publish or apply a universal travel allowance. The required margin depends on the machine’s thermal duty, measurement uncertainty, assembly variation, and consequences if the floating ring reaches an end stop.

A drawing review should identify both extreme conditions: the condition in which the shaft is shortest relative to the housing and the condition in which it is longest. In each case, the intended movable ring or internal bearing displacement must remain within its permitted range. If the movement runs out in either direction, the arrangement can develop unintended axial preload or thrust load.

Choose the locating support from axial load direction

Select the locating support according to the shaft-position requirement and the source, direction, and reversibility of axial load. The locating bearing may need to react thrust from helical gears, bevel gears, impellers, screws, couplings, process pressure, gravity on a vertical shaft, or externally applied actuator loads.

Start by documenting the following on the assembly drawing or load case sheet:

• Which component creates axial force.
• The expected thrust direction for normal operation.
• Whether thrust reverses during reversing, coast-down, startup, upset, or maintenance modes.
• The magnitude of radial and axial load in each operating case.
• The required shaft position relative to gears, seals, impellers, encoders, or other components.
• Whether the locating support is accessible for retention, inspection, and service.

The locating support does not have to be at the drive end or non-drive end by rule. It should be placed where it best controls the required functional position and provides a practical load path into the housing. Thermal gradients, seal location, gearbox geometry, assembly sequence, and maintenance access can all change the decision.

Radial bearings capable of carrying combined radial and axial loading may be used at a locating support, but the exact choice depends on direction and magnitude of thrust, speed, misalignment, lubrication, stiffness, and desired clearance or preload. SKF lists deep groove ball bearings, matched angular contact ball bearing pairs, double-row angular contact bearings, tapered roller bearings, and certain other designs among bearings that may serve a locating function, subject to the application. That list is not a universal interchangeability statement.

For example, a deep groove ball bearing may be suitable where catalog-rated axial capacity, speed, clearance, and operating conditions align with the load case. A matched angular contact pair may be selected where controlled bidirectional axial guidance and stiffness are required. A tapered roller arrangement may be appropriate for substantial combined loading but requires careful adjustment, mounting, lubrication, and thermal review. Use the exact catalog and mounting documentation for the selected series rather than transferring capability from another bearing family.

NSK similarly states that the locating bearing absorbs radial and axial forces and that its rings must be axially secured on the shaft and in the housing. See its bearing arrangement guide for the general arrangement principle.

Select how the non-locating support will float

There are two common ways to create the required axial displacement at the non-locating support.

Internal displacement within the bearing

Some bearing designs can accommodate axial displacement internally. N and NU cylindrical roller bearing designs are common examples when configured according to the manufacturer’s instructions. Their ring and flange geometry permits one ring to move axially relative to the roller-and-ring assembly while both rings can remain axially secured in their respective seats.

This is often useful where a sliding outer or inner ring fit would create an unacceptable risk of ring creep or fretting. It does not mean every cylindrical roller bearing can be used this way. The exact design, cage, internal geometry, permitted displacement, load direction, and mounting arrangement must be checked in the manufacturer’s documentation.

Sliding displacement of one bearing ring on its seat

For an inseparable bearing used in the non-locating position, axial displacement can be created by allowing one ring to slide on its seat with an appropriate close sliding fit. The other ring, often the ring requiring interference fit because of rotating load conditions, remains axially retained.

The fit cannot be selected from the need to float alone. Review the rotating load zone, risk of ring creep, shaft or housing material, seat surface finish, temperature, corrosion environment, vibration, and expected axial motion. A ring that must move axially should not become unintentionally clamped by an end cover, shoulder, seal carrier, spacer, retaining ring, or distorted housing bore.

SKF’s axial location guidance explains the general distinction: in a non-locating position with a movable ring, the interference-fitted ring is secured while the other ring remains free to move. It identifies cylindrical roller bearings used for internal displacement as an exception in which both rings are axially secured.

Prevent unintended axial over-constraint

Over-constraint is a frequent arrangement error because each individual part can appear reasonable in isolation. A bearing may be identified as floating in a parts list, while an end cover, spacer stack, or shoulder quietly blocks the intended movement after assembly.

Trace the axial restraint path for each ring in both directions. The review should include:

Interference fit alone is generally not a sufficient means of axial location on a cylindrical seat because a loaded ring can creep. For locating supports, ring retention should be designed explicitly. Conversely, adding positive retention to both rings of a non-locating inseparable bearing can eliminate its required movement path.

The general design risk is well illustrated in MIT’s FUNdaMENTALS of Design material, which warns against over-constraining bearings during mounting. The correct acceptance criterion remains application-specific: the assembled arrangement must not create axial loading or preload beyond the bearing and machine design limits as parts are tightened or temperatures change.

Verify the arrangement before release and during assembly

A bearing arrangement should be reviewed as a documented load path, not approved from a schematic alone. Before release, identify the locating support directly on the drawing and show the intended axial movement path at the non-locating support.

Use a pre-release checklist:

1. Define all radial and axial load cases, including reverse thrust and abnormal conditions.
2. Identify which bearing support fixes shaft position and why that location is required.
3. Calculate relative shaft-to-housing movement across the specified temperature and tolerance range.
4. Specify the bearing series, internal clearance or preload condition, ring fits, and axial retention features from the selected manufacturer’s guidance.
5. Confirm the non-locating support has sufficient available movement in both axial directions.
6. Review every shoulder, cover, spacer, nut, snap ring, and seal carrier for accidental restraint.
7. Confirm the housing construction maintains bore geometry and does not pinch the movable ring after bolting.
8. Define assembly inspection points, including ring seating, end-cover clearance, orientation, lubrication, and shaft rotation checks.

During assembly, isolate electrical energy, depressurize connected systems, prevent shaft rotation, and follow the machine and bearing manufacturer’s instructions. Apply mounting force only through the ring being fitted; forcing load through rolling elements can damage raceways before operation. Heating methods, maximum temperatures, cleanliness requirements, lubricant quantity, clearance measurement, and preload procedures must come from the specific bearing and machine documentation.

After assembly, inspect the evidence that the floating function remains available. Depending on the design, this may include measured end clearance at an end cover, confirmation of the intended ring’s seating and fit, shaft-position measurement, or an approved functional check during controlled run-up. Do not interpret free manual rotation alone as proof that thermal movement is adequate.

A sound locating and floating bearing arrangement has one clear axial reference point, one verified accommodation path for relative movement, and retention features that match the selected bearing design. If thrust direction, thermal profile, fits, or bearing geometry are uncertain, stop at the design-review stage and obtain the bearing manufacturer’s application guidance before releasing the housing and shaft details.