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Thermal Insulators on Micrometers...

Discussion in 'METROLOGY - MEASURE, SETUP & FIT' started by Splat, Jul 2, 2017.

  1. Splat

    Splat Active User H-M Supporter-Premium

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    If the operator is only handling a micrometer for a few seconds at a time, as a home machinist possibly might.... how important are thermal insulators on a micrometer? Are they a definite must-have on micrometers for you?
     
  2. markba633csi

    markba633csi United States Active Member Active Member

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    Apparently they do make a difference, maybe a tenth?
    Mark
     
  3. mikey

    mikey Active User H-M Supporter-Premium

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    I don't worry about it. My Mit and Etalon mics have them and my Helios and B&S don't - haven't noticed a difference in use. When boring, I use a mic stand that eliminates this variable.
     
  4. kd4gij

    kd4gij United States Active User Active Member

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    Unless you are working in a temperature controlled environment, and working in tenths you wont se a difference.
     
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  5. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    When your shop is at 98.6 degrees F. there's nothing to worry about.
     
  6. chips&more

    chips&more United States Active User Active Member

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    Is somebody on this site working for NASA?
     
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  7. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    An interesting question. Steel has a linear expansion coefficient of around .000012"/" - ºC. For a six inch micrometer, if you were able to raise the frame temperature by 5ºC (9ºF), the expansion would be .00036". In practice, I expect that the temperature change caused by holding the micrometer would be no more than a degree or so, if that.

    My micrometer set has the insulated grips but I measured my 5" standard and then gripped the micrometer by the uninsulated parts of the frame for about a minute. I could detect no significant change in the reading. (within .0001")
     
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  8. grzdomagala

    grzdomagala Austria Iron Registered Member

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    Tesa micrometer with 25mm range and 0.002mm resolution moved visibly after a few seconds in hand. Don't know why so much - maybe the frame distorted due to nonuniform temperature.
    It wasn't nasa - just a prototype of small high speed spindle.
     
  9. Nogoingback

    Nogoingback United States Active Member Active Member

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    You could see it move .002 mm? You have good eyes! :)
     
  10. ch2co

    ch2co United States Grumpy Old Man H-M Supporter-Premium

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    Just tried this with my 2" Starrett micrometer and starting from a shop temp of 65F I inserted a 1" reference rod and zeroed it then warmed
    the thing (just the frame) up as much as I could in my hands which are considerably below internal body temp, which I measured to be 86.7F.
    The difference was less than a ten thousandth". There must be an expansion of the metal frame going on, and no doubt can be measured, but...
    I think this is a moot point for any home machinist. Yes there will be a tiny difference, but there are a LOT of other variables to worry about that
    have much greater consequences for the finished part.
     
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  11. higgite

    higgite General Manger - Proofreading Dept. Active Member

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    Seems to me that for hobby machining, one could drive oneself wacko chasing thermal expansion from just handling stuff. Not only will the mic in one hand expand, but how about the work piece or gauge block being held in the other hand?

    I work a lot on the ignorance is bliss principle. ;) ymmv

    Tom
     
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  12. mikey

    mikey Active User H-M Supporter-Premium

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    Yeah, we can measure it but cutting it is another thing! Then again, we're hobby guys and have all the time in the world to split microns. In a job shop ... I suspect not so much.
     
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  13. ch2co

    ch2co United States Grumpy Old Man H-M Supporter-Premium

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    How about when we are turning something on the lathe, for example, we stop the lathe and measure the diameter etc. of our part and, at least me,
    never even think of the expansion of the part even though it's quite often too hot to touch? Those of you that have coolant flowing over the part
    are, of course, not included in this thought experiment. The expansion of the part is far greater than the expansion of the measuring device warmed
    by our hand, and yet I have never found a part that measured correctly while in the hot state that changed after it cooled. This of course is actually
    false, but for any of our needs, is a moot point.
     
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  14. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    The bottom line is that, as hobbyists, we make parts to fit together in assemblies. The only surfaces that are anything close to critical are mating surfaces and very few of them require measurements to tenths of thousandths.
     
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  15. grzdomagala

    grzdomagala Austria Iron Registered Member

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    Skf catalogue calls js5 tolerance for standard bearing sit. On a 15mm shaft it's +- 0.004mm. If you want "machine tool" quality (for example for small high speed spindle) its js4 +-0.0025mm - almost exactly +-tenth.
    Maybe holding this tolerance is not necessary (maybe even futile if all you have is a minilathe) but im not a pro - i don't have experience to tell where it's safe to skimp.

    Wysłane z mojego GT-N7100 przy użyciu Tapatalka
     
  16. higgite

    higgite General Manger - Proofreading Dept. Active Member

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    Not futile, if you have enough time on your hands. I have been known to sneak up on a critical OD of a round matching part by using a strip of emery cloth to buff off the last few nanomillimicrons while spinning it in a mini or bench lathe. Can get a spectacular finish like that, too.

    Tom

    P.S. I didn’t measure the final OD though. It was trial and error fit. I don’t have a measuring tool with that fine of resolution.
     
  17. mikey

    mikey Active User H-M Supporter-Premium

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    Many a good workman has brought a part in on size with a lathe file and sand paper. You're in good company, Tom.
     
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  18. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    My luck usually is. It mic's .001" over, put some emery to the surface, get it looking pretty. Measure again and it's .0005" under! Hello Loctite. And I keep three different flavors of it, too!
     
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  19. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    Been there, done that....more times than I care to think about. It is amazing how high those tiny little ridges can be.

    I'm a little smarter now. When I have a critical diameter, I will cut slightly oversized and do my polishing to get a sense of how much material will be removed. Then I will make any correction and make my final cut.
     
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