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IndustryArena Forum > Mechanical Engineering > Linear and Rotary Motion > Ball screw bearings, finding preload
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  1. #1
    Join Date
    Jan 2007
    Posts
    17

    Ball screw bearings, finding preload

    I bought new bearings for the ball screws on my mill, SKF 7204 BECBP.
    http://www.skf.com/skf/productcatalo...did=1230020204

    I have read conflicting information on how to install them.
    It appears the best way would be installing them back to back, but I have read the inner rings should be clamped tight and also read the outer rings should be clamped tight when there back to back.

    I am not sure I understand the proload either and can't decipher what it is form the SKF website.

    This is what I think I need to do, find what the preload is (weight) and measure the defection of the outer race when this weight is placed on the bearing.

    Take this measurement X 2 and shim between the races of the two bearings and clamp tight the inner rings and I will have the correct preload.

    Do I have this right.
    How do I find the preload

    Your help is greatly appreciated,
    Bruce

  2. #2
    Join Date
    Mar 2006
    Posts
    2712
    The specified preload is ground into the pair of bearings. When you clamp the inner races together in a back to back (DB) pair, they are preloaded.

    Clamping the outer races to a fixed shoulder in a housing prevents axial motion of the ball screw.

    No shimming is required.

    Dick Z

    ADD: The SKF bearing numbers listed above do not indicate preload or accuracy class. 7204 BECBP indicates a 7200 series 20mm bore, 40 deg. contact angle, paired bearings with a glass fiber cage. Missing are grade such as P4 and preload letter such as A = light preload; B = preload greater than A; C = preload greater than B; CA = small axial internal clearance. This info is from an SKF General Catalog.
    DZASTR

  3. #3
    Join Date
    Jan 2007
    Posts
    17
    I bought these because they said thery were ABEC 5
    It also says on the bearing 0770 and explorer, I found this on the SKF website.


    SKF Explorer angular contact ball bearings are manufactured only as bearings for universal matching with P6 dimensional accuracy and P5 running accuracy.

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