Bearing Questions for DC Brushless Motor

Discussion in 'General Electronics Chat' started by slor, Sep 22, 2013.

  1. slor

    Thread Starter New Member

    Sep 22, 2013
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    I'm rebuilding the 70s-vintage Pioneer M-502E DC motor on a Roland tape delay. Since the last one of these, my source for the bronze bottom bearings has disappeared (the top bearing is a sealed ball bearing and still somewhat available).

    With some arduous searching, I've found a similar bronze bearing (8mm height vs. 10mm on the original, I'm guessing this won't make a tremendous amount of difference?).

    However, I've come across ball bearings that should fit in the bottom position. My question is: Is there any benefit in using one type of bearing over another? Noise, reliability, longevity, etc.

    Many thanks, in advance!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Ball bearing are a bit more expensive, this is one reason Oilite bronze was used, but they tend to dry up if not kept lubed.
    If you can fit a ball bearing, that may be the way to go.
    Max.
     
  3. slor

    Thread Starter New Member

    Sep 22, 2013
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    Thanks, that was my gut instinct too but I have little experience with these things!
     
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
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    McMaster Carr sells Oilite bearings. Once one of these bearings dry up their useful life is over. Re-oiling them just buys you time.

    If you can fit a sealed bearing in that space you'd be much better off, it'll only be a few dollars more depending upon where you buy it.
     
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  5. ian field

    Distinguished Member

    Oct 27, 2012
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    There's a tendency for bronze bearings to be fairly compact - you may have to consider needle-roller bearings rather than ball types. You can usually order them with the outer race and if you're lucky you might find one that fits both the shaft & the housing.

    Otherwise; order to fit the existing shaft with the biggest outer that's too small for the housing and have a small engineering company turn a packing sleeve to fit.
     
  6. Metalmann

    Active Member

    Dec 8, 2012
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    "My question is: Is there any benefit in using one type of bearing over another? Noise, reliability, longevity, etc."



    The general answer when you are designing machinery is--ball bearings for shafts with lighter weight, higher RPMs.
    Oilite bearings were first designed for large, heavy, low RPM, shafts.

    That varies a lot nowadays.

    Both are being used in different applications.

    For your use, I'd use ball bearings for both, if handy.
     
  7. #12

    Expert

    Nov 30, 2010
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    If you're going to buy machine shop time, it's cheaper to cut down the extra 2mm (mentioned in the first post) than to cut a round shim with both inside and outside surfaces, and both ends needing to be cut.

    If you do want to make a sleeve, I use a drop of Loc-tite to keep the sleeve from spinning in the (degreased) hole. Of course, Loc-tite won't stick to oilite, so try to make it an interference fit. If the machinist isn't good enough to do an interference fit, I make lots of little dots with a prick punch to damage the surface, kind of like knurling. If that doesn't work, take it back and complain at the machinist.:mad:

    and, yes, there is a reason for different types of bearings. Ball bearings are a bit noisy, but they last longer than sleeve bearings. For instance, the outside fan motor for an air conditioner should be ball bearings, but the inside fan should be bushings. The crankshaft in your car uses sleeve bearings, not because they are less noisy, because they are a lot cheaper than ball bearings. Needle bearings have a lot more bearing surface than ball bearings, so they go in places that must remain tight and smooth running for a longer time, like universal joints in your drive shaft.
     
    Last edited: Sep 23, 2013
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The bottom bearing doesn't get any radial forces like the top bearing, so is much less critical (and less likely to need replacing).

    Provided it is not so worn that it is flopping around loose I would just use a good medium weight oil on it and leave the bottom bronze bearing in place.
     
  9. PackratKing

    Well-Known Member

    Jul 13, 2008
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    The major trouble with oillite bushings, is once the load-bearing surface glazes, they no longer pass oil to where the rubber meets the road, and fail quickly.

    In these applications, avoid "3-in-one" like a plague, because it is one !!!
    3/1 will dry up and turn to something resembling foul smelling scorched snot in a bearing / bushing that gets even warm in normal use !!

    More DIY " mechanics " as well as so-called " professional " HVAC contractors ruined more very expensive Bell & Gossett, Taco, etc., hot water circulating pumps using 3/1 in the impeller shaft oil wicks, than Carter has Peanuts... :p

    I got to rebuild hundreds of them... from the 1/12 hp household, to up to 50 hp industrials, where the brass / bronze impeller can cost over a thousand bux by itself, nevermind the castings and shafts, when the impeller gyrates on worn bushings in tight tolerances found in waterpumps...
    20 Wt. non-detergent is your best bet...
     
    Last edited: Sep 23, 2013
  10. Metalmann

    Active Member

    Dec 8, 2012
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    "Ball bearings are a bit noisy, but they last longer than sleeve bearings."


    Not necessarily true.

    Before "Oilite" brand bearings/bushings, machines used poured Babbitt bearings, poured right onto the shafts in place. Bearings on some of those old machines lasted for 100 years.
    All depends on the application.

    I've seen balls go bad in just a few hours. Usually due to misalignment.;)

    Or, a frigid wife.
     
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  11. PackratKing

    Well-Known Member

    Jul 13, 2008
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    I'll vouch for this, lock, stock, and barrel !!! :eek:
    Bearings of ANY stripe never cease to amaze me for the pounding they can and do endure...
     
    Last edited: Sep 23, 2013
  12. #12

    Expert

    Nov 30, 2010
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    Right. It depends on how massively over sized the bearings are. If sleeve bearings always lasted 100 years, I wouldn't be replacing a dozen evaporator fan motors a year.
     
  13. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Wow !!... Only a dozen??... How do you rate... :D
     
  14. ian field

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    Oct 27, 2012
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    A car crankshaft uses shell bearings because its quite tricky stretching a ball-race over all the lumpy bits on a crankshaft.

    Ball (and sometimes roller) are fairly common on single cylinder motorcycle engines.
     
  15. MaxHeadRoom

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    Jul 18, 2013
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    Automotive shell bearings are generally Babbit Metal.
    Max.
     
  16. #12

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    Shell bearings, sleeve bearings, bushings, all of them don't have moving parts, so I mix up the names pretty much all the time.:rolleyes:
     
  17. ian field

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    I've heard them described as "lead-indium" on one occasion - I never bothered looking it up at the time.
     
  18. #12

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    A little googling comes up with lead-indium being a harder alloy than lead-tin. Used for a (better) surface on the rod bearings in a car engine.
     
  19. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    In Australia we call them "white metal" bearings.
     
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  20. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The best engine bearings are Clevite 77. There made with a steel base layer, copper/lead layer, then a electroplated babbitt layer that goes against the shaft. But any shell type bearing needs a constant oil pressure, because the shaft actually rotates on the oil film, not the bearing. No oil is what makes a shell bearing wear out.
     
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