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Thread: Bearings

  1. #46
    Registered User Little Scrapper's Avatar
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    Re: Bearings

    My reamer was delivered today, it's .4995" so a half thou under.

    Also. Bearings.

    The correct bearing has a different part number than what I received. More on that later. I'm currently working on the nose ribs and a router solution for making parts. The bearing/bracket/aileron situation is coming up fast so trying to be prepared.

    The correct bearing is not a ZZ part number but rather a 2Z. The ZZ bearing calls for a flush inner race and the 2Z designation is for the bearing that has a extended inner race.

    I could use either. Trying to think that through currently.

  2. #47
    Registered User BoKu's Avatar
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    Re: Bearings

    Quote Originally Posted by Dan Thomas View Post
    ...6061T6 would stretch easily. 2024T3 would be tighter and 7075T6 might split because it's so hard and brittle.
    All aluminum alloys have approximately the same Youngs Modulus, so within their elastic range, for a given stress they all stretch the same amount. The difference between 7075-T6 and 6061-T6 is that the 7075 will stretch farther before it transitions from elastic to plastic and becomes permanently deformed. However, for the fractional percent of bore diameter we're talking about here, that's way down in the weeds.

    Having worked with a lot of 7075-T6, I can say that in practice it is not particularly any more brittle than any other aluminum. The big difference between it and 6061 is that it drills a whole bunch nicer. The chips are smooth and feathery, whereas 6061 chips come out jagged and gummy, and tend to grab and lacerate fingers. I'd rather work 7075 any day of the week.

    --Bob K.
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  3. #48
    Registered User BoKu's Avatar
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    Re: Bearings

    Quote Originally Posted by Little Scrapper View Post
    ...The correct bearing is not a ZZ part number but rather a 2Z. The ZZ bearing calls for a flush inner race and the 2Z designation is for the bearing that has a extended inner race...
    I buy rather a lot of bearings, and I don't think that's how it works. Near as I can tell, ZZ and 2Z are slightly different designations for bearings shielded on both sides.

    http://www.engineerstudent.co.uk/bea...explained.html

    [Edit add] I sniffed around the web, and I couldn't find an extended-inner-ring version of the R3. But it could be my Google-Fu is weak today.

    --Bob K.
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  4. #49
    Registered User Little Scrapper's Avatar
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    Re: Bearings

    Bob, I could certainly be wrong. Check out the screen shot of the bearing and read the data. I believe this bearing would make more sense.


    Click image for larger version. 

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  6. #50
    Registered User Little Scrapper's Avatar
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    Re: Bearings

    On the other hand, it's about .015" extension on each side which is basically nothing.

  7. #51
    Registered User BoKu's Avatar
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    Re: Bearings

    Quote Originally Posted by Little Scrapper View Post
    Bob, I could certainly be wrong. Check out the screen shot of the bearing and read the data. I believe this bearing would make more sense.


    Click image for larger version. 

Name:	Screenshot_20190307-172528~2.jpg 
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    Good find; if that bearing matches it's specs, it certainly does have the extended inner ring you're looking for. The spec sheet says that the trade equivalent is R3ZZ, which may or may not be the case, but that's probably a reasonable price for the extended inner ring feature.

    In my shop our standard low-capacity bearing is the 626-2RS, which has 19mm OD and 6mm ID. We use flanged bushings inserted into the ID that adapts them to 0.190" for 10-32 hardware such as AN3 bolts; the flanges on the bushing extend the inner ring. Those bushings cost us about $2 each, so if you can get the extended inner ring built into the bearing you're probably coming out ahead.

    --Bob K.
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