tip 111 - determine shaft and housing fits.pdf

7/29/2019 Tip 111 - Determine Shaft And Housing Fits.pdf

1/3

Bearing Shaft Housings and Fits

To determine the shaft and housing fits required for a particular application, one must consider such variables as

load, ambient temperature, the type of bearing and the type of shaft and housing. The fit, or amount of

interference that exists between mating components, can be devised into three resultant categories: press fit,transition fit and loose fit.

An improper fit selection may allow the bearing to creep on the shaft or in the housing. Creep is defined as the

inner ring slipping on the shaft or the outer ring slipping in the housing. This occurs when the interference fit is

not sufficient for the operating conditions. As a result, creep can cause wear, ring fracture and excessive

vibration.

On the other hand, an excessive interference fit will eliminate the bearing internal clearance and cause a rise in

operating temperature. A shaft interference fit expands the inner ring; similarly, a housing interference fit

compresses the outer ring. It will also make the installation of the bearing more difficult and more susceptible to

damage during installation.

Typically, an inner ring rotating application will use a tight or interference fit on the shaft, and the housing willuse a loose or clearance fit. Likewise, with an outer ring rotating application, the opposite is true.

Bearing fits are selected by reviewing the application details, general guidelines and with experience. When

reviewing the application, the following questions should be answered:

What is the bearing size and type?

Is the application inner or outer ring rotating?

What is the load direction and condition?

What kind of shaft and housing are being used?

i.e. -Is the shaft solid or hollow?

-Are the shaft and housing of steel or aluminum

construction?

For more information on shaft and housing fit selection, consult your local NTN Technical Support Team.

To make a proper fit selection, one must consider the type of load, the operating environment (i.e., ambient

temperature), the type of shaft or housing, and the type of bearing. The two tables on the overleaf give some

general recommendations for the selection of fits for radial bearings.


2/3

Interference:

"Press fit" or "loose fit" are terms used to distinguish the amount of interference that exists between two mating

components.

Load Conditions Fits

Rotating inner ring load

Inner ring : stationary

Outer ring : rotating

Direction of load : constant

Inner ring :

interference fit

Outer ring : loose fit

Stationary inner ring load


Outer ring : rotating

Direction of load : constant

Inner ring : loose fit

Outer ring :

interference fit

Stationary inner ring load

Inner ring : rotatingOuter ring : stationary

Direction of load : rotating with

outer ring

Inner ring :

interference fit

Outer ring :

interference fit

Rotating inner ring load


outer ring : rotating

Direction of load : rotating with

outer ring

Inner ring :

interference fit

Outer ring : loose fit

Proper fit selection ensures that the

inner and outer rings do not slip

with respect to the shaft or housing.

"Creep" occurs when the

interference is not sufficient for the

operating conditions.

Creep causes abrasive wear, shaft

vibration, and excessive

temperature rise. On the other

hand, an excessive interference fit

will eliminate the bearing operating

clearance and also lead to atemperature rise. Excessive

interference fits also increase the

difficulty of assembly and the risk of

bearing damage during assembly

(i.e.,Brinelling). Both of the above

conditions can ultimately lead to

poor bearing performance.

Table 1 gives the general criteria for

selection of interference with respect

to the basic load conditions. 1) Interference fit is preferred for separable bearing.

Table 1

ISO Nomenclature

Standard metric dimension tolerances for bearing shaft diameters and

housing bore diameters are governed by the lnternational Standards

Organization (ISO). Fits are designated by a letter followed by a

number. Letters in lower case (e.g., j6) refer to fitting onto a shaft

while letters in upper case (e.g., H7) refer to fitting into a housing.

Figure 1 summarizes the common shaft and housing fits. The actual

shaft and housing tolerance for various fit designations depend on the

respective diameter and are listed in ISO shaft and housing fit tables

which are available from NTN. Contact your local NTN representative.


3/3

Fit With Shaft

Ball

bearings

Cylindrical

and

tapered

ball

bearings

Spherical

roller

bearingsBearing type Load conditions

Shaft diameter

mm

Shaftfits

- 18 - - h5

18 - 100 - 40 - js6

100 -

20040 - 140 - k6

Light or

fluctuating

variable load

- 140 - 200 - m6

- 18 - - js5

18 - 100 - 40 - 40 k5

100 -

14040 - 100 40 - 65 m5

140 -

200100 - 140 65 - 100 m6

200 -

280140 - 200 100 - 140 n6

- 200 - 400 140 - 280 p6

Normal to

heavy load

- - 280 - 500 r6

- 50 - 140 50 - 100 n6

- 140 - 200 100 - 140 p6

Rotating

inner ring

or

indeterminate

direction

load

Very heavy

or

shock load- 200 - 140 - r6

Inner ringaxial

displacement

required

All shaft diameters g6

Cylindrical

bore bearings

Static

inner ring

load

Easy axial

displacement

of

inner ring

not

required

All shaft diameters h6

Tapered bore

bearings

(with sleeve)

All load All shaft diameters h9/IT5

Courtesy NTN BEARING CORPORATION OF AMERICA

tip 111 - determine shaft and housing fits.pdf

Documents