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Ran ballnut off ballscrew on the knee of mill

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  • Ran ballnut off ballscrew on the knee of mill

    I lowered the knee too much on my mill and I think I have somehow done the impossible(according to the factory) and run the ball nut off the screw. I think that because when I turn the crank for the knee nothing happens. I jacked the knee up with a hydraulic bottle jack and it rises and then stops after about 10mm. If I turn the crank when it is tight the knee raises 5mm which is the pitch of the ball screw and then nothing happens. The handle turns but does not raise the knee. My thinking is the lower balls in the nut have come out and only the top balls or some of the top balls are still there so once the nut turns and those balls get circulated the knee stops raising. Not sure really. I am waiting on the plans from the factory to see exactly how the whole thing is assembled before I start tearing it down. I really didn't need this headache right now. I have enough on my plate. SPFD!
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Sorry you’re having problems with your balls. Have you asked the wife for any assistance?

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    • #3
      I just went and asked her if she would help me get my balls off the floor. She gave me a sour face and told me that I know my balls are too heavy for her to lift!
      Location: The Black Forest in Germany

      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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      • #4
        FYI
        Putting the balls back into the nut is not an easy job
        besides being a pain to do, you also need to mike the balls and sort them by size
        There are two sizes , small and larger ( by .025mm ?)
        The smaller ones are really spacers so the larger ones can roll in the same direction without skidding.
        so you alternate the balls during reinstallment
        Rich
        Green Bay, WI

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        • #5
          Originally posted by Rich Carlstedt View Post
          FYI
          Putting the balls back into the nut is not an easy job
          besides being a pain to do, you also need to mike the balls and sort them by size
          There are two sizes , small and larger ( by .025mm ?)
          The smaller ones are really spacers so the larger ones can roll in the same direction without skidding.
          so you alternate the balls during reinstallment
          Rich
          Hey you are right! I just reached down and one seems bigger than the other. Don't blame me. Oxford started it! Truthfully I didn't know a ballnut had two different sizes of the balls. I have put them back together in the past but maybe that is why they didn't seem quite right. Now I have to try and remember which machines they were on. I can't even remember what I had for lunch. SPFD!
          Location: The Black Forest in Germany

          How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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          • #6
            Rich is right it is not an easy job but if you put a little bit of grease on them when inserting them back in they will go back together a lot easier

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            • #7
              Originally posted by Rich Carlstedt View Post
              FYI
              Putting the balls back into the nut is not an easy job
              besides being a pain to do, you also need to mike the balls and sort them by size
              There are two sizes , small and larger ( by .025mm ?)
              The smaller ones are really spacers so the larger ones can roll in the same direction without skidding.
              so you alternate the balls during reinstallment
              Rich
              Aren't the larger balls going to roll against the smaller ones just the same??

              JL......

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              • #8
                I would think the knee would have bottomed out before that happens. must be a different setup than my Bridgeport.

                JL......

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                • #9
                  In memory of a certain motorbike mechanic… “Clumsy Bastard!”

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                  • #10
                    The ballscrew is I think 40mm diameter so at least the balls won't be very small relatively speaking. Shut up Oxford!
                    Location: The Black Forest in Germany

                    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                    • #11
                      Originally posted by Black Forest View Post
                      The ballscrew is I think 40mm diameter so at least the balls won't be very small relatively speaking. Shut up Oxford!
                      We may as well just shut this thread down now. Lol

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                      • #12
                        On a related note, I’ve never had to do it with ball screws but I have played 52 ball pickup with linear bearings a few times.

                        Once on my own doing before I new what was going on with them, a few times on someone else’s doing.

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                        • #13
                          Originally posted by JoeLee View Post
                          Aren't the larger balls going to roll against the smaller ones just the same??......JL.....
                          let me try to verbalize it just have to use the right words as I can't draw a picture at the moment

                          The balls are loaded against each other and the large balls engage both the top and bottom of the groove
                          As the balls roll to the right, they are both turning clockwise (CW) so the contact point between the two balls would see double wear rates because
                          they are both turning CW . the right side of the left ball is moving downward and the right ball has it's left side (contact point) moving upward.
                          This would stop the balls dead, they would not be friction free. Remember now, this is because the balls are tightly loaded in the races .
                          Now if you put a slightly smaller ball between them ( snugly) , that ball will turn Counter Clockwise (CCW) and only places force between the two larger balls.
                          So even though the ball is running backwards , it is not engaged with the top or bottom surfaces as it is smaller than the distance between them.
                          now the ball may touch either of the top and bottom , but because of grease and the lack of force on the top/bottom , it exerts little force (drag )

                          On Ball Bearings, the makers use "cages" to provide spacing between rolling elements.
                          On Needle Bearings there is room ( ie- no load )between the needles so rolling elements are free ( as long as lubed) and spacers/cages not needed IN SOME CASES

                          Back to Ball Nuts . ...The size difference of the two balls is based on the load expected by the maker.
                          We all know that balls will deflect ( get smaller) under a load, so the maker has to figure out how much
                          and then he can determine what clearance he wants for the smaller ball.
                          if you rebuild a ball nut that has some wear, you may want to increase the size of the replacement balls by .0001" or so
                          to compensate for Race wear

                          Hope this helps
                          Rich

                          Green Bay, WI

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                          • #14
                            Thank you for the explanation Rich.
                            Location: The Black Forest in Germany

                            How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                            Comment


                            • #15
                              Hey, i found it
                              Go here and read down at the 'Ball Screw: paragraph.
                              This is a supplier of precision balls to industry
                              Many Home shoppers have no idea that balls can be purchased in ALL sizes ( like .5015 " for example )
                              This not only allows rebuilding any bearing or nut, but it a great resource for " Ball Sizing"
                              when you push a precision ball through a bore and get a super round and Smoooth surface ( then you throw the ball away )
                              Rich

                              https://precisionballs.com/ball_mate...ction.php#A420
                              Green Bay, WI

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