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Thread: Powermatic planer, knife grinder spindle bearings

  1. #1
    Join Date
    Sep 2016
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    Modesto, CA, USA
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    Powermatic planer, knife grinder spindle bearings

    I bought an older grinder for a powermatic 18" planer older. The motor bearings seem to be okay. Hard to say with a universal motor with brushes. The spindle needs new bearings they feel and sound crunchy. I can not read any bearing numbers due to heavy factory green paint. Since it is belted down from 10,000 rpm at the motor I assume I can use rubber sealed bearings. The rpm is probably under 3000.
    The arbor is odd. I see nothing holding in the bearings, no snap rings, probably just a tight push fit. I also see nothing holding the spindle shaft in the bearings. It looks like a straight shaft just pushed in. Nothing obvious stopping it from coming off the end. There is no axial load to speak of so they. may have let it float a bit? The belt will prevent it from moving far. It does have a cross hole in the shaft for a cotter key?

    I know for a tool post grinder they need high quality bearings with very little runout. How critical should these be. I assume better then the average motor quality stiff sold everywhere?
    Bill D

    I do not know the age but the cord is grounded with a two prong plug and. seperate ground clip. I am guessing early 1960's or older
    Last edited by Bill Dufour; 01-21-2023 at 4:36 PM.

  2. #2
    Join Date
    Dec 2005
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    West Lafayette, IN
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    6,527
    This would probably get more attention over at OWWM. make sure to post some pictures so people know what you’re talking about.

  3. #3
    Join Date
    Sep 2016
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    Modesto, CA, USA
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    For future information seekers the spindle bearings are Fafner 9101 NPP. I found two new ones on ebay for about $12 delivered.
    I took off the grinding wheel and there is a set screw under it. I think this holds in one bearing as a slip fit. Unfortunately all but one of six grinding wheels that came in the deal are much too small a bore. I need to find out the recomended grit for the wheel.
    Bill D

  4. #4
    I think the Fafner 9101 is the same as a 6101 bearing, which cost less than two bucks each.

  5. #5
    Join Date
    Feb 2014
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    Lake Gaston, Henrico, NC
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    The wheel grit is Very coarse, but I don't remember what it is. In the '80's they came with white grinding wheels that worked like a charm.

    edited to add: and matched the racing stripe.

  6. #6
    Join Date
    Mar 2010
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    Somewhere in the Land of Lincoln
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    Bill what is the spindle size and do you know what the maximum diameter can be? You want to know what the spindle RPM is as well. Trust me you DON'T want a grinding wheel to explode especially if there is no containment guarding. You would be shocked at how far the pieces can fly. 10,000 RPM at the motor? That sounds backwards to me. Usually the spindle is stepped up from the motor.

  7. #7
    Join Date
    Sep 2016
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    Modesto, CA, USA
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    Bruce you may be right about the bearings. I bought the exact same ones since I do not really know what bearing class is needed. Of course the ones on the bay may not be higher class. For wood working it may not matter so much. I know lathe tool post grinders often have some very expensive low tolerance bearings.
    It is definitely belted down a lot from the motor speed. I believe the grinding wheel starts off as 4.5 inch diameter.
    Bill D.

  8. #8
    Join Date
    Mar 2013
    Location
    Trenton SC, in the CSRA
    Posts
    509
    A ball park approach for bearing identification is to measure, ID, OD, and width of the old bearing. Determine the bearing type, ball, roller, etc., and the seals required. The numbers stamped on bearings are codes for those measurements and styles. If you can measure, you can find a replacement. YMMV.

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