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Mounting bearings with a tapered bore by measuring radial clearance prior to mounting

If obtaining an exact radial internal clearance or preload is not critical or if SKF gauges are not available, it is possible to determine the required axial drive-up distance. To do this, locate the assembled bearing at a reference point on the shaft and measure the radial internal clearance with a dial indicator positioned on the outside surface of the outer ring. This method does not take into account that the outer ring is compressed when mounted with an interference fit in the housing. To compensate for this, it can be assumed that the outer ring raceway diameter will decrease by 80% of the diametric interference fit. The procedure comprises the following steps:
  1. Mounting the inner ring (trial)
    • Coat the tapered shaft seat with a thin layer of light oil and push the assembled bearing in place until the bearing bore makes good contact with its seat.
    • There should still be clearance between the outer ring and rollers.
    • Keep in mind that small bearings may have only 15 μm internal clearance prior to mounting and that an axial drive-up of 0,1 mm causes a clearance reduction of ~ 8 μm.
  2. Measuring the internal clearance prior to mounting
    • Place a spacer ring onto the shaft and position it between the bearing inner ring side face and drive-up device. The spacer, which must be parallel to the bearing inner ring side face, is there to guide the outer ring side face when measuring clearance (fig. 1).
    • To measure the radial clearance, place a dial indicator on the outer ring circumference and set the indicator to zero.
    • Holding the outer ring firmly against the spacer, move the outer ring up or down, and measure the total displacement. This measured distance is the radial clearance in the bearing, prior to mounting.
    • Do not apply excessive force to the outer ring. Elastic deformation may cause measurement errors. 
  3. Determine the required axial drive-up distance Ba (→ Adjusting for clearance or preload) remembering to include the allowance for outer ring interference fit, if one exists.
  4. Determining the spacer ring width
    • Measure the distance L between the bearing side face and the shaft abutment (fig. 1). Take measurements at different diametrical positions to check accuracy and misalignment. The difference between the single measurements should not exceed 3 to 4 μm.
    • Calculate the required width of the spacer ring using

    B = L - Ba


    required width of the spacer ring
    mean measured distance from the bearing inner ring to the abutment

    the required axial drive-up distance to achieve the desired clearance reduction or preload (→ Adjusting for clearance or preload)
  5. Mounting the bearing (final)
    • Grind the pre-machined spacer ring to the required width.
    • Remove the assembled bearing, mount the spacer ring, and drive up the inner ring roller and cage assembly again until it firmly abuts the spacer ring.
    • Locate the inner ring using a suitable locking device.
    • Heat the housing to the required temperature and mount the outer ring.
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