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  1. #1
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    Default Chrome Steel Ball Measure with Digital Micrometer

    I currently have a thread running that describes issues with the X-axis ball screw off my CNC turrett mill:
    - https://metalworkforums.com/f308/t20...rew-nut-re-fit.
    My focus at the moment is the purchase of new balls, slightly larger than the existing.
    But what size are the existing balls ?

    I have fairly typical hobby machinist gear, mix of new Chinese and ex-industrial.
    There are calibration and operational issues with all of it.

    As part of my investigation I purchased 1/4" balls from the local CBC dealer.
    CBC cannot quote a batch number or quote a size for these balls.
    I measure them at 6/10 thou " undersize.

    New balls are available from the US, at a price, about $200 for 110 balls.
    But, my measurement of the existing balls, 3/10 thou " oversize, is based on the use of my measuring equipment.

    So, I am considering the purchase of a new 0 - 25 mm digital micrometer, 0.002 mm accuracy, typically available from Ausee for $83.

    Need some help:
    - comments on the accuracy of the Ausee micrometer,
    - volunteer to measure my balls with known calibrated equipment (I am in Kingswood).

    Thanks in advance for any comments,
    John.

  2. #2
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    Apr 2012
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    Healesville
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    Default

    Hi John, this is a differant chinese mic but should be much the same as the ausee one, i measured an old (could have been owned by Noah) 1/4" gauge block with 3 differant mic's.

    cheers, shed20190925_104728.jpg

    Sent from my SM-G900I using Tapatalk

  3. #3
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    Default

    If you want to size balls, gauge block set, granite plate and very accurate parallel.

    Make a bridge and balls undersize will roll under it. Go from there.

    I did not think of that, Phil mentioned it to me.
    Gold, the colour of choice for the discerning person.

  4. #4
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    Default

    Hi Guys,

    I guess like some of you I have several micrometers in the 1" inch (25 mm) and 2" inch (50 mm) ranges, all come with a setting piece ! Non of those measure the same on any of the micrometers or callipers, both digital and dial types. So I only trust the Moore & Wright ones that I know and assume are to be right. I also have a single 1" gauge block that I know is within 5 micron at room temperature, only the M&W 1" and 2" inch mics give me the same reading using this block.

    So you need to calibrate one of your mics and use only that one as a reference, buying a new expensive one will only serve to show you a difference from the ones you currently have and still may not be accurate. Also accuracy and repeatability are not the same thing.

    JMTPW.
    Best Regards:
    Baron J.

  5. #5
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    Default

    Happy to measure them at work for you, all our mics are tested annually (+/- 1 micron at that size). If I ask really nicely, I might even be able to use our high precision mic which reads to 0.1 micron.

  6. #6
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    Default

    The surface plate approach has appeal.
    I tried a set-up, but couldn't convince myself of its repeatability/accuracy.
    I don't need a quality Go-Nogo gauge, I want an absolute measure to a few microns.

    My granite plate is many years out of certification, but all tests to date show it to be good,

    I do have access to a recently purchased gauge block set.
    Calibration of a new micrometer at the target size should not be a problem.

    My precision inspection test stand with a lever-operated Mercer 1/10 thou "DTI is very usable, but its base plate shows wear and I assume the probe tip is also worn.
    Calibrating with gauge blocks could be quite different to measuring balls.
    Ex-factory, balls are supplied to size and tolerances of a small fraction of a micron.
    I just need a known good ball to set up the DTI.

    Options are:
    - I acquire the necessary equipment and measure/use one of my balls,
    - an external party measures one or more of my balls,
    - a certified ball is purchased,
    - someone lends me a known good ball.

    John.

    John

  7. #7
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    elanjacobs,
    You posted while I was writing !

    That is a very kind offer.
    Lets give it a few days, then I will PM you if I need to take you up on it.

    John

  8. #8
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    Default

    I am sure some years ago there was a seller on eBay selling ball bearings in the 1 micron range and where cheap, nowhere near thAt price you where quoted.

    Have you considered double nuts to preload them?
    I have my set of ballscrews for my mill, but ordered double nuts with them all to preload. That was years ago and I now see the coupled double nuts are cheap, I would have went that way these days.
    Using Tapatalk

  9. #9
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    Default

    Dave,
    Thanks for the comments.

    Some progress:
    1. A good mate has a Mitutoyo 3 or 4 digit metric digital micrometer, with a nice stand.
    As soon as practicable, I will visit with my balls and we will do some measurements.

    2. Made up some gauge blocks and test rolled the balls through the gap.
    The CBC 1/4" balls just touch at 6.345 mm, roll free at 6.35 mm.
    The old balls refuse to pass through the 6.35 mm, either roll or touch at 6.355 mm.
    So my measurements are not too far off.

    3. After discussing with a couple of knowledgeable machinists, I will purchase the Ausee micrometer.

    4. Considering suggestion that I contact the ball supplier in the US and ask if they would accept a sample lot of my balls, then supply balls 5 micron larger.

    5. For completeness, should repeat (4) above with CBC, or other suggested local supplier.

    Just starting to get confidence that we can resolve this.
    John.

  10. #10
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    It is a bit hard measuring balls with a mic as the anvils are spherical, you really want flat anvils and something that repeats more accurately, something like a mitutoyo 523 snap micrometer.
    I have a new one somewhere?

  11. #11
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    Quote Originally Posted by shedhappens View Post
    It is a bit hard measuring balls with a mic as the anvils are spherical
    Unless you've bought one specifically made that way, mic anvils are lapped very flat (to the point of being wringable)

  12. #12
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    Default

    Yes elan, you are correct, getting confused in my old age and probably thinking about internal mics

  13. #13
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    Quote Originally Posted by electrosteam View Post
    As soon as practicable, I will visit with my balls and we will do some measurements.
    It will be good if your friend can help you measure your balls accurately...

    A good example of how precision is not easy.

  14. #14
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    Also a good example of how ball measurement is a team activity.

  15. #15
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    Metrology is hard !
    Miniscule variations in procedures, environment and temperatures give significant variations.

    My mate arrived with his Mitutoyo 4 digit metric digital micrometer (with mirror finish anvils).
    We confirmed the sizes I was measuring with my DTI test stand, as calibrated off the slip gauges.
    The slip gauges are metric Grade 2, 0.45 - 1 micron.

    We went through the original balls using the test stand, zeroed with the slip gauges.
    Tried a pair of slip gauges, 5 + 1.35 mm, but found the results not repeatable.
    Used a single 6.5 mm slip gauge, and checked the zero many times during the test sequence.
    The nominal ball size is taken to be 1/4" = 6.35 mm, so nominal DTI reading should be - 0.15 mm = -59/10 thou".

    As balls measured, stored them in 6 containers each labelled with their size:
    - 55/10 thou" 1,
    - 56/10 thou" 1,
    - 56.5/10 thou" 3,
    - 57/10 thou" 84,
    - 57.5/10 thou" 12,
    - 60.5/10 thou" 1.
    Re-checked several times, quite repeatable to 0.5/10 thou".

    The single value that best characterizes the size is -57/10 thou".
    This is 2/10 thou" bigger than the nominal 6.35 mm, or actual size 6.355 mm.

    Note that in an earlier post, I reported these balls as roll/touch when rolled through slip gauges set to 6.355 mm.
    But the tolerance would be more than +/- 1 micron.

    Had lunch a couple of days ago with a small group of skillfull and experienced machinists.
    One had a Mitutoyo 0-10 mm micrometer with graduations at 0.002 mm, on a barrel that was about 3x normal diameter.
    It was arranged as a heavy-duty bench mount and read some sample 57/10 thou" balls at 6.357 mm.

    I reviewed the construction of typical digital micrometers.
    They are not a linear graticule with a reader, they simply count revolutions, and provide a software derived value.
    Hence subject to the same short-range pitch errors as ordinary micrometers.
    A Mitutoyo one I discovered uses a much coarser thread, and a larger diameter counting wheel.
    The coarser thread provides a more accurate progressive pitch, the larger diameter better precision on the counting wheel.
    Until I can afford a quality digital micrometer, I cannot see the benefit of an economical one.

    With the ball diameter and spread determined, this thread can be closed.
    Refer to the thread linked in the OP for further developments on the CNC ballscrew nut refit.

    Thanks to all the contributors and those that viewed.
    John.

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