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Accuracy of D1-4 mounting..spindle bearing.... whatever?

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  • Accuracy of D1-4 mounting..spindle bearing.... whatever?

    Alarm bells began to ring when I found my ER32 collect chuck for mounting MT3 in my lathe was off centre, so I started checking for the error, hoping that it is a bent collet chuck.

    The first check I did was the face of the D1-4 mount which is part of the spindle, it shows nary a flicker on my DTI. So I moved on to the taper and found 0.012mm 'dip' on one side. I cant see any evidence of it having been damaged and the DTI does not show a smooth cyclic motion as I would expect from being 'merely' off centre.

    Next step was to put a morse taper in, after cleaning the spindle tapers, clocking off the protruding part of the taper I can see the same thing, a sort of 'dip' of about the same as measured on the camlock taper, again, it is in just one position.

    So what is likely to be the cause, bad bearing maybe?

  • #2
    Is the dip in the reading always in the same spot relative to the spindle?

    I would stick a DTI into the spindle taper and see how that reads. Maybe clean it out real good with some steel wool and inspect for burrs or chips too.

    Doesn't a D type spindle mount have an external taper for the backplate? I'm asking because if so I'd compare that to the internal taper to see if the low spot is in the same position.

    KEJR

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    • #3
      Originally posted by KEJR
      Is the dip in the reading always in the same spot relative to the spindle?

      I would stick a DTI into the spindle taper and see how that reads. Maybe clean it out real good with some steel wool and inspect for burrs or chips too.

      Doesn't a D type spindle mount have an external taper for the backplate? I'm asking because if so I'd compare that to the internal taper to see if the low spot is in the same position.

      KEJR

      I dont have a finger DTI to reach inside the spindle taper and use the D4-1 camlock has an external taper and that is the first taper I checked against.

      The dip does always seem to be in the same position but maybe I should do that test again then run the spindle for a minute or two and see if the dip 'moves'.

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      • #4
        I do not recommend doing this to everyone, but I have taken a VERY LIGHT grind off all the surfaces on a few new Taiwan lathes that I have had. Not that they were off much,but I am a stickler for accuracy. I even grind the tapered spindle hole. They are usually off a tenth or so,but when I get done with them,they are dead nuts true. I use a Themac grinder for this. I check the mating fits of the short taper on D type spindles with blue against chuck back plates,and of course the spindle hole taper,too.

        Hardinge spindles are finish ground true in situ also.

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        • #5
          Gwilson, thanks for the information but I wont mess with the finish of the spindle until I am sure the bearing is not the culprit.

          It does seem rather odd that the DTI shows a 'dip' rather than a smooth cycle over the entire revolution which I would expect if anything had been ground off centre.

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          • #6
            Another possibility would be a headstock gear with a chip in it or a similar irregularity.
            Don Young

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            • #7
              Thanks Don, something like that would be a possibility. I have never crashed the carriage into the chuck but I have had at least one crash which caused the motor belt to squeal, I checked for chips then and didnt find any.

              However, working on the principal of trying the easy things first I nipped the bearing pre-load a micro-tad or so then ran it high speed for 5 minutes. The DTI then showed 0.018mm runout on the end of a MT adapter, there is not so much of a 'dip' as I was noticing before and checking the factory test sheet showed that is just a little better than they measured!

              Now I am managing to confuse myself not knowing if I am reading things right and also not being experienced enough to know what would be typical for this class of lathe.

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              • #8
                If your indicator has a little ball bearing at the end like mine does, you may want to take a real close look at it. One little spec of dust or a nick can make that needle move.

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                • #9
                  Dti

                  Originally posted by Boostinjdm
                  If your indicator has a little ball bearing at the end like mine does, you may want to take a real close look at it. One little spec of dust or a nick can make that needle move.
                  I have one which has a small nick in the side of the ball which can cause just what you are describing , no idea how it got there as its on one I purchased at a sale .
                  Michael

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