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Thread: Bearing housing tolerance on a CNC lathe

  1. #1

    Default Bearing housing tolerance on a CNC lathe

    Hi guys,

    I am a little bit confused, I will ask a machine shop to make me some housings on a CNC lathe.

    The bearing construction outside tolerance is -6 to -17 microns. I want a housing that would be like a tight enough to hold it in place but that could be pushed in and out by hand.

    What tolerance grade should I use? I JS4 ? This is a +3 -3 tolerance. Do you always have to use this ISO tolerances or you can just make up ure own, like.. I dunno 0 to -6 microns...

    Can a regular CNC lathe turn parts in a micron tolerance?

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  2. #2
    Join Date
    Dec 2006


    If you have the make and model of the bearings used you can checkup the housing diameter tolerances specified by the maker.

    I seriously doubt that the housing tolerances specs be in microns.

    Best regards


  3. #3


    A push fit as you describe has practically zero tolerance. It must be .008mm clearance. Any larger will seem loose and smaller will be difficult to assemble without a press or very careful tap tap tapping with deadblow hammers.

    We've done fits like this for many years with electric motor endbell bearings. There are some batches of bearings that come small enough to spoil the feel of the fit. We hand fit each bearing to each housing if the customer is willing to pay for it.

    It would be a practical impossibility to guarantee such a fit on any batches of parts being assembled in random order. While the cnc lathe could potentially hold a tolerance of .01mm, asking them to hold half of that is a tall request. I'd go for opening up the housing a bit on the plus side, and perhaps using loctite compound to fill the gap whenever the bearing is permanent fit.

    First you get good, then you get fast. Then grouchiness sets in.

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  4. #4



    Thanks all for the answers.

    A 0.01mm tolerance you mean + or - 0.01 making it 0.02 error or + or - 0.05 so you would have a 0.01 possible error?

  5. #5


    I would recommend using the tolerances determined by the bearing manufacturer. Sometimes these are not the slip fit you would like. Often, they require an interference fit.

    When a slight interference is specified, warming the housing and/or cooling the bearing will permit a "slip" fit at assembly. When the housing and bearing normalize to ambient temperature, the specified interference will be there.

    This is important in machine spindles, especially in high speed or heavily loaded units.

    Too bad we lost NC Cams, he would have given us a great sermon on the subject.

    Dick Z


  6. #6


    the part wont be that precise, its just a aluminium housing. I will just ask the guys to machine and see when its good and after that run the cnc to repeat, it probably can repeat a part within 0.005 microns ( oops edited ) consider mm

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