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Shaft and Housing Fits for Bearings

written by: kkaarthic • edited by: Lamar Stonecypher • updated: 11/29/2008

This article deals with the importance to be given for the fits for the mounting of the bearings on the shafts and housings. The basic criteria’s to be considered for the fits are also explained in detail.

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    Bearings are important members in a mechanical system and proper care must be ensured for supporting and mounting of the bearings in their working atmosphere. A major area that contributes for this is the fitment of the bearing in the shaft and the housing on which it is mounted on.

    Hence many factors are to be considered to decide upon an idealized fit which has no interference or looseness. The major criterion that influence a fit for a bearing are as follows:

    · The operating condition of the bearings which involve load, speed, temperature, etc.

    · The requirements by the application for the rigidity and rotational accuracy of the bearing

    · The machining tolerances applicable on the mounting areas of the bearing.

    Fit on Shaft and Housing:

    An interference fit is normally applied in areas of bearing mounting on the shaft. But all conditions may not be required for an interference fit. The circumstances which require an interference fit for a bearing on a shaft are

    · When the total mass center shifts are to be avoided ( Like preventing the shaft from moving away from the bearing, leaving it in its place)

    · When the bearing is subjected to heavy radial loading

    · When there is any possibility of occurrence of any external vibration that can cause fretting and wear

    · When there is a real need for heat transfer, the heat generated in the shaft is made to flow through the bearing and then to the housing via the bearing.

    · When chances of no axial clamping is possible on the bearing to prevent it from moving axially.

    The use of interference fit should be cautiously made since there is every possibility of distortion of the raceway of the bearing and reduction in radial internal clearance of the bearing.

    A loose fit can also be used for mounting the bearings. They are really advisable on the following conditions

    · The bearing is subjected to axial clamping forces which prevent the bearing to move axially in any way.

    · The ease of assembly of the bearing is very much required and important.

    · Any axial movement of the bearing is required for thermal expansions and in some cases to accommodate spring loading of the bearings.

    Ensuring these points during design will enable the trouble free operation of the bearing for its lifetime.