Centring a rotary table horizontally on a mill table.

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Centring a rotary table horizontally on a mill table.

Home Forums Beginners questions Centring a rotary table horizontally on a mill table.

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  • #54229
    ZigFire
    Participant
      @zigfire
      Hello Everyone,
      I performed my first setup of a rotary table horizontally on a mill table last night, using a dial test indicator in the central hole to centre the table to the vertical mill axis.
      I achieved this within 0.01mm runout which was very much adequate using the X and Y feeds. I then proceeded to tighten the X and Y axis and off course lost centre to a certain degree.
      My question is how do you centre the table then avoid losing centre after tightening up the gibbs for machining?
       
      Any tricks or tips greatly appreciated.
      Cheers
      Michael
       
       
       
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      #5139
      ZigFire
      Participant
        @zigfire
        #54230
        Bogstandard
        Participant
          @bogstandard
          Michael,
           
          It sounds as though you have a little trouble with your axis lead screws. I don’t know the layout of your mill, but many mills have adjustment in the nuts to take out the free play.
           
          Also, if you tighten up your gibs a tiny amount, that might prevent the table moving as much as you tighten up the locks. Or actually put your locks on, but not too tight, as you come to final setting. Then when you do the final lock tweak, it shouldn’t move so much.
           
          If when you tighten up as it is now, anything under 0.05mm (0.002″) should be acceptable. That is a normal sort of tolerance figure, and isn’t usually noticeable on final assembly of parts made.
           
          You can sometimes take getting perfection a little too far, and all you end up with is frustration, attempting to reach the impossible.
           
          Bogs 
          #54231
          ZigFire
          Participant
            @zigfire
            Hi Bogs,
            Interesting reply, thanks. 
             
            After tightening up I lost concentricity by around 0.1mm, so double your 0.05mm.
            If I continue to have issues perhaps I could loosen slightly the hold down bolts on the rotary table, centre the table  X and Y, tighten the axis then lightly tap the table back to centre and tighten the holdown bolts.
             
            PS fully agree with the “perfection too far” comment by the way. Man’s gotta know his limitations..and his machines as well. (please forgive the Clint Eastwood quote)
             
            Cheers
            Michael
            #54232
            ZigFire
            Participant
              @zigfire
              Hi Bogs,
              Interesting reply, thanks. 
               
              After tightening up I lost concentricity by around 0.1mm, so double your 0.05mm.
              If I continue to have issues perhaps I could loosen slightly the hold down bolts on the rotary table, centre the table  X and Y, tighten the axis then lightly tap the table back to centre and tighten the holdown bolts.
               
              PS fully agree with the “perfection too far” comment by the way. Man’s gotta know his limitations..and his machines as well. (please forgive the Clint Eastwood quote)
               
              Cheers
              Michael
              #54233
              Dusty
              Participant
                @dusty
                Michael
                           I agree in some part with Bogs assesment of your problem. I think the problem is with your gibs, I believe that your gibs are set too slack. You can check the play in the table by locking everything up lashing up a clock on the end of the table and giving the opposite end of the table a bit of a push and shove having slackened the lock. This should show how much slack is in your gibs. Theoretically if you removed the leadscrew and pushed the table up and down you should feel resistance, it should feel quite stiff. When applying the locks you do not need to torque wrench them up, just a nip should suffice. This will also help with your ordinary milling.  Locking everything up and then tapping the rotary table into position is making hard work of a simple task.
                #54237
                Alexander13
                Participant
                  @alexander13
                  I am not sure if this will help but here goes.
                  I have recently completed a machining course at a local college and we used a simple but effective method for centring a rotary table on a vertical mill.  We measured the diameter of the centre hole and turned a piece of material down to fit it with a slight chamfer on the leading edge to aid fitment into the center centre hole, at the other end we turned it down to fit a collet.  We then fitted the alignment tool we had made into the appropriate collet in the mill head and adjusted the the rotary table until the tool fitted the centre hole of the table, then just to check, we rotated the table 360 degrees while the alignment tool was still in the centre hole of the table and the mill head rotated with it.  We then checked the set up and it proved to accurately aligned within the tolerances of the mill, so in future the set up can be repeated quite quickly and easily. Also the axis that are to be locked up can be done so while the alignment  toot is holding the table in location.
                   
                  #54240
                  WALLACE
                  Participant
                    @wallace
                    Sounds like your gib strips are moving around  – the cure is to pin them (silver steel + reamer) so they can’t move ! (or at least not along their length ).
                     
                    W.
                     
                    #54247
                    ZigFire
                    Participant
                      @zigfire
                      Thanks for the tips guys, I’ll check the gibs and any table slackness and reduce the elbow grease when tightening.
                       
                      Cheers
                       Michael
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