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  • Press fit for bearing

    Could someone please tell me what would be a slight press fit for a bearing that has an .875 outside diameter. I need to bore a hole in a piece of 12L14 for this bearing and Im not sure how much to undersize this hole. If you cant tell Im new to all of this, so any help or sarcasm would be greatly appreciated.

  • #2
    .8741 to .8745 is the chart recommended sizing.

    ------------------
    Barry Milton
    Barry Milton

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    • #3
      How are you measuring the bored hole? I only ask this because I had a bit of fun to start with when measuring a hole and expecting a good fit- to my horror the hole came out larger than I wanted despite me taking much care in boring it. That's when I learned that the dial indicator I used would read three thou small, with the hole therefore being three thou larger than indicated.

      I don't know if this is a standard, but this slight overlap of the inside jaws prevents the thing jamming when you try to open it from fully closed. If this small overlap wasn't there, the inside jaws could 'pass' each other, preventing the caliper from opening.

      If your final passes are to test fit something, you can take a few passes to remove small amounts of material each time, then test fit. Easy enough. But if the hole has to be a fixed size smaller than the thing that fits it, such as when needing a shrink fit of parts, or a press fit, then you'll have to be able to know exactly how large your bored hole is strictly by measurement. Do some experimenting on scrap to find out this difference in your indicator's reading between inside and outside measurements, and only then can you rely on it to tell you the true diameter of a bored hole.

      Just thought I'd bring this up again for those who didn't know, or who have forgotten to factor this in.

      [This message has been edited by darryl (edited 06-13-2005).]
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        For that sort of work I will make a plug guage from brass. I cut it with a taper of .001 over one inch. This allows easy measurement to .0001 based on how far the guage fits in the hole. Be careful not to jam it in the hole.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          Darryl, is this bore measurement task a good job for inside mikes and a calibrated 0-1" outside mike? Or even a simple GO-NOGO gauge?



          [This message has been edited by Last Old Dog (edited 06-13-2005).]

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          • #6
            The dial caliper has it's limitations in measuring inside diameter.

            Depending on the size of the hole, small hole gages or telescoping gages are your best bet. Get good ones, Starrett, B&S, Mitutoyo or Lufkin. Avoid the low priced imports.

            They take a little practice to get the technique, but once mastered, very accurate readings can be made.
            Jim H.

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            • #7
              I think Evan brings out a good point here. Sure it’s nice to have just the “rightâ€‌ measuring instrument but - if not - one can make something very easily to do the job just as well – if not better!

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              • #8
                I have a set of the hole gages but theyre imports, the few times Ive tried them I didnt trust them. Im going to try the go-no-go gage and see if I can get it that way. This is a mount for a bearing for my little 7x14 cross-slide, in case any of you have tried it. Thanks for the help.

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                • #9
                  Loc-Tite products are the great equalizer in applications such as this. Especially in a lightly stressed installation as this, they can make life much easier.

                  A go-no go gage will only tell you if the hole is too large or too small, it will not tell you how much material to remove.

                  The tapered plug gage, if you can make one, will only tell you the diameter of the top of the hole, not if it is straight or tapered. It is also of little use in a shallow hole.

                  Get good tools and become proficient in their use. It is all part of the process.
                  Jim H.

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                  • #10
                    It works for me JC. I have built a lot of projects using ball bearings that are a light press fit. After a while you end up with a handy set of plug gauges. If you do the boring right the top of the hole should be the same size as the middle. If it isn't then you have more basic problems to deal with first. For my designs through holes are the rule. It is pretty easy to come up with ways to retain the bearings. Stepped shafts and collars come to mind.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      No arguement here, the proper measurement device is what should be used. Having no such inside measurement tools myself, I've learned to manipulate the dial indicator to the point where I can trust the readings to within a half thou or so. This certainly takes some learning and practise, but it can be done. I like to repeat the readings a few times, just to see if they are consistent, and if they are, then I have passed the test of taking a reading properly, and the indicator has passed the test of giving a consistent reading. While doing the multiple readings, I check to see that the indicator shows .000 when closed each time.
                      I always have a few bits of precision rod around, and I use these to check the indicator and the bored hole. I keep old ball bearing races around for the same reason. I have thought to do a slight 'taper grind' on the outside of an old race just to use it as a hole gauge when boring for that size bearing, but I haven't yet done that. I think that would be handy for whatever common sizes of bearing a person would normally use.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        And this from the peanut gallery.

                        I have a cheap chinese digital calliper.

                        why couldn't you shapen the outside jaws to a V shape, slip indicater inside hole, zero meter, bring it out and close jaws to get minus reading of hole.? Is that possible?
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                        • #13
                          A lathe mandrel (tapered) works as a nice gauge, and you can use it in the lathe as well.

                          Kap

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                          • #14
                            I would make it .001" undersize. If the bearing is on a shaft I would subtract the
                            amount the shaft is oversized and subtract the .001" undersize of the housing from the bearing ball or roller bearing original clearances.
                            example: If a bearing has an original roller clearance of .005" and is on a shaft that is .001" oversize and is pressed into a housing that is .001" undersized.
                            Then subtract .002" from the original .005"
                            roller clearance of .005",this leaves .003"
                            roller clearance. It is possible to take up
                            the entire roller clearance if these things are not considered. This would cause the bearing to run hot.

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                            • #15
                              0.001 undersize is far too much even for a tight press fit. Bearing manufacturer specs for a light press fit for that size of bearing in an ABEC 5 spec (+0 -.0002") call for -.0002 to -.0004 at the most for the outer race housing.
                              Free software for calculating bolt circles and similar: Click Here

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