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Thread: Two Micrometers Don't Agree

  1. #41
    Boolit Master jmorris's Avatar
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    A man with one clock always knows what time it is, a man with two is never sure.

    Maybe you need three and ditch the one that doesn’t agree. Or you can do like most machine shops and have them calibrated by an outside source.

    https://www.transcat.com/calibration...libration-labs

    Decent micrometers come with standards so you can test them yourself at either end of their range and you can use gauge blocks somewhere else if you like.



    A precision instrument that’s not precise isn’t worth much around here, about as much as a Chinese C clamp.
    Last edited by jmorris; 05-08-2019 at 09:31 AM.

  2. #42
    Boolit Master
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    You can have a lot of sayings and rules but standards, Jo-blocks and calibration all cost money. If you have a mike that you got at a good price having it calibrated by an specialty house will cost more than the mike is worth. It is better if you learn enough to set zero on your 0-1 mike yourself. You are not likely to have to set it at all but if you do and take care of the mike you will never need to set it again.
    For the most part mikes larger than 0-1 never get used because much of the work can be measured with calipers. Few reloaders have the slightest use for gage blocks nor would they know how to use them nor would they have a surface plate, height gage or a sine bar. Common sense is a lot more economical than spending money like water just because you think you can make the results perfect. You can't and it will cost you a lot of money to find that out.

    If you only have one clock you only THINK you know what time it is. You cannot prove anything for sure.

    Quote Originally Posted by jmorris View Post
    A man with one clock always knows what time it is, a man with two is never sure.

    Maybe you need three and ditch the one that doesnít agree. Or you can do like most machine shops and have them calibrated by an outside source.

    https://www.transcat.com/calibration...libration-labs

    Decent micrometers come with standards so you can test them yourself at either end of their range and you can use gauge blocks somewhere else if you like.



    A precision instrument thatís not precise isnít worth much around here, about as much as a Chinese C clamp.
    Last edited by EDG; 05-08-2019 at 12:35 PM.
    EDG

  3. #43
    Boolit Master jmorris's Avatar
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    I can prove that one of the OP’s micrometers is reading incorrectly because he claims they don’t read the same.

    You can say it doesn’t matter and it might not, you can say a caliper (not a precision instrument in many circles) is “good enough”, that too may be correct but one of his micrometers, if not both are not telling the truth. Some folks like to know what is right and wrong, others can build things with no measuring tools at all.

    I only have one clock the shop, it receives the amplitude-modulated time signals the .gov sends out therefore can only be expected to determine the beginning of a second with a practical accuracy uncertainty of Ī 0.1 second.

    Doesn’t matter much because it doesn’t have resolution that precise and I wouldn’t need it, if it did.

    Likely like the OP’s different measurements won’t hurt him but if he wants to know what one is correct, there are methods that can eliminate his uncertainty.
    Last edited by jmorris; 05-08-2019 at 05:56 PM.

  4. #44
    Boolit Master
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    You might want to re-read what I said. I said nothing of what you claim.
    Now you want to try again?
    Where exactly did I say it was it does not matter? Where did I say it was good enough?

    This is what it really says

    It is better if you learn enough to set zero on your 0-1 mike yourself.

    What I really said is your suggestion to have micrometers calibrated by an outside calibration house is a waste of money if you know how to set the zero of your 0-1 micrometer yourself.

    Second it matters little how accurate you THINK your clock is you have no way to prove it.
    I have set my time pieces to NIST time also. That does not mean they hold that accuracy for more than a second. It is humorous that you admitted that perfect accuracy of your clock is not necessary. So it does appear that less than perfect can be good enough for you.

    You might want to re-read what I said because it is not what you are claiming.



    Quote Originally Posted by jmorris View Post
    I can prove that one of the OP’s micrometers is reading incorrectly because he claims they don’t read the same.

    You can say it doesn’t matter and it might not, you can say a caliper (not a precision instrument in many circles) is “good enough”, that too may be correct but one of his micrometers, if not both are not telling the truth. Some folks like to know what is right and wrong, others can build things with no measuring tools at all.

    I only have one clock the shop, it receives the amplitude-modulated time signals the .gov sends out therefore can only be expected to determine the beginning of a second with a practical accuracy uncertainty of Ī 0.1 second.

    Doesn’t matter much because it doesn’t have resolution that precise and I wouldn’t need it, if it did.

    Likely like the OP’s different measurements won’t hurt him but if he wants to know what one is correct, there are methods that can eliminate his uncertainty.
    EDG

  5. #45
    Boolit Master jmorris's Avatar
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    So it does appear that less than perfect can be good enough for you.
    Sadly it is, no matter what resolution you are able to measure it’s still not perfect.

    You can have calipers that will get you close to 3 decimal places. Other indicators can get you much closer to perfect, yet so far away.



    Perfect is a never ending number of zeros though. Why we work in tolerances. Some things need to be close, some don’t matter much at all and some need to be “really” close. “Really” to a guy on a backhoe might be a number of feet, a carpenter it could be inches, a machinist, tens of thousandths of an inch. Kind of like how long a minute is depends on what side of the bathroom door your on.

    I should have said “one” vs “you” in my statements but the reply was across the board of things posted in this thread (vs quoting each and every post or context).

    This “you” falls into the “might not matter” category, in my book.

    I've been reloading since '65 and have never seen anything that needed absolute accuracy to a tenth.
    If you can load and not tell the difference between a .100 and .001, you don’t need calipers, micrometers or anything more accurate.
    Last edited by jmorris; 05-08-2019 at 10:20 PM.

  6. #46
    Boolit Master uscra112's Avatar
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    Being a guy who has written not one but TWO MIL-I-45208 manuals for my various employers, I'm enjoying all this.
    flectere si nequeo superos, acheronta movebo

  7. #47
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    I have to say this thread is turning into a P*****g contest.

    Zeroing a mic and calibrating a mic are not the same thing. When you zero a mic you are setting it to your feel against a standard of a known size. Calibration is a different animal. It ensures that the tool is within the industrial and Mil Spec standards for the type/class of measuring or gaging tool. The current standard is https://www.quality-control-plan.com...with-iso-9001/ Very few high end new measuring tools will fully meet these standards when new and they don't get better with usage.

    Most new tools come back from the initial calibration with limitations and some are flat out rejected. For indictors Brown & Sharpe tend to be the best. I prefer Intrepid however out of apx 30 purchased for the shop none ever made it through initial cal. without needing a limited Cal sticker. For Brown and Sharpe about 1/2 would fully pass calibration. For mics and dial calipers B&S and Etalon tended to have the fewest limitations.

    For gage blocks three sets of new SPI were rejected on initial cal. The replacement Starrett sets all fully passed the initial cal.

    My shop was required to follow DLA Aviation standards.

    My most accurate and expensive measuring tool is my Mahr 20 Millionth 0 - 1 pressure mic. I also have several free plastic dial calipers and yes they are good enough for measuring group size at the range or is that a 6mm bolt or 1/4" . I have about 10K worth to measuring tools that are in-between the two extremes that are selected depending on requirements.
    Last edited by M-Tecs; 05-08-2019 at 10:49 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  8. #48
    Boolit Master
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    The usual preference for precision measurement is to have an instrument with 10X the resolution of the measurement needed. When that is not available the default is an instrument with 4X the resolution needed.
    Not only are the parts we make NOT perfect due to manufacturing tolerances but the tools we use to measure them are not perfect either. Sooner or later you have to accept less than perfect because nothing is ever perfect. However there is not one thing to be sad about. The entire world runs fine on everything being less than perfect
    If you confuse .100 and .001 no tool is going to be much use to you unless you are framing a house or something of similar precision.

    Quote Originally Posted by jmorris View Post
    Sadly it is, no matter what resolution you are able to measure it’s still not perfect.

    You can have calipers that will get you close to 3 decimal places. Other indicators can get you much closer to perfect, yet so far away.



    Perfect is a never ending number of zeros though. Why we work in tolerances. Some things need to be close, some don’t matter much at all and some need to be “really” close. “Really” to a guy on a backhoe might be a number of feet, a carpenter it could be inches, a machinist, tens of thousandths of an inch. Kind of like how long a minute is depends on what side of the bathroom door your on.

    I should have said “one” vs “you” in my statements but the reply was across the board of things posted in this thread (vs quoting each and every post or context).

    This “you” falls into the “might not matter” category, in my book.



    If you can load and not tell the difference between a .100 and .001, you don’t need calipers, micrometers or anything more accurate.
    EDG

  9. #49
    Boolit Master
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    Zeroing an 0-1 mike is setting it to a known standard and that standard is ZERO length.
    That is perfectly adequate for a handloader with a decent mike that shows no apparent error end to end.
    The usual handloader with one ordinary 0-1 mike does not need to know 9858, 45208, ISO 9001 or any of that stuff. He does not need gage blocks to set his 0-1 mike either. We do not need to drag in dial indicators when the subject is an ordinary 0-1 micrometer.

    You may feel your 10K worth of measuring instruments was a big deal for your shop. I have bought Renishaw CMM probes that cost 3X that. I have bought 50 inch optical comparators and CMMS even more expensive. No matter how much you spend there is always some shop somewhere that has bigger or better equipment. But none of that equipment is needed to set a simple mike to zero so it can be used by a handloader.


    Quote Originally Posted by M-Tecs View Post
    I have to say this thread is turning into a P*****g contest.

    Zeroing a mic and calibrating a mic are not the same thing. When you zero a mic you are setting it to your feel against a standard of a known size. Calibration is a different animal. It ensures that the tool is within the industrial and Mil Spec standards for the type/class of measuring or gaging tool. The current standard is https://www.quality-control-plan.com...with-iso-9001/ Very few high end new measuring tools will fully meet these standards when new and they don't get better with usage.

    Most new tools come back from the initial calibration with limitations and some are flat out rejected. For indictors Brown & Sharpe tend to be the best. I prefer Intrepid however out of apx 30 purchased for the shop none ever made it through initial cal. without needing a limited Cal sticker. For Brown and Sharpe about 1/2 would fully pass calibration. For mics and dial calipers B&S and Etalon tended to have the fewest limitations.

    For gage blocks three sets of new SPI were rejected on initial cal. The replacement Starrett sets all fully passed the initial cal.

    My shop was required to follow DLA Aviation standards.

    My most accurate and expensive measuring tool is my Mahr 20 Millionth 0 - 1 pressure mic. I also have several free plastic dial calipers and yes they are good enough for measuring group size at the range or is that a 6mm bolt or 1/4" . I have about 10K worth to measuring tools that are in-between the two extremes that are selected depending on requirements.
    EDG

  10. #50
    Boolit Master
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    I know what 45208 means to a handloader at home with an ordinary 0-1 mike - exactly nothing.

    Quote Originally Posted by uscra112 View Post
    Being a guy who has written not one but TWO MIL-I-45208 manuals for my various employers, I'm enjoying all this.
    EDG

  11. #51
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    Quote Originally Posted by EDG View Post
    You may feel your 10K worth of measuring instruments was a big deal for your shop..
    No those are personal tools that I paid for out of my own pocket for my civilian position before I worked for the government. They are now utilized in my home shop. What I purchased for the government shop was more like 1.5 million in inspections tools.

    Knowledge is free and I am more than a little surprised that you seem to have a problem with sharing how industry deals with this issue.

    For a very large percentage of reloaders a plastic dial caliper is adequate. Same for the very low cost mics. Some of those are actually very good.

    We could have a much larger discussion on what is realistic accuracy of various tools in novices hands and what accounts for inaccuracies in both novice and experienced hands but you argue that setting at zero for a 0-1 is all that is need yet you also state there is no reason to tolerate error .0004" in a mic. Those two positions don't go together very well.

    This covers basic calibration of a mic

    https://www.qualitymag.com/articles/...ng-micrometers

    These results mirror my experiences on how the average mics track. Not sure I agree with the cause. While not always the case the more you pay the more precision you tend to get. In the late 80's and early 90's the Polish mic imports were junk. They are much better today so I think the price verse precision is less than it used to be. None of the B&S or Elton mics ever failed or had limited cal. for the initial cal. SPI always came back with limitation and a couple failed initial cal.

    With gage pins or blocks the class or grade spells out the level of precision. That is not the case with mics. Just because a mic reads in tenths doesn't mean its accurate.

    https://rick.sparber.org/am.pdf

    Gage block also have different grades depending on intended usage.

    https://www.prattandwhitney.com/Cont...Tolerances.asp

    For those interested in the history of gage blocks

    https://www.nist.gov/sites/default/f...ns/mono180.pdf
    Last edited by M-Tecs; 05-09-2019 at 11:07 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  12. #52
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    Quote Originally Posted by EDG View Post
    If you confuse .100 and .001 no tool is going to be much use to you unless you are framing a house or something of similar precision.
    Who's confused?

    Come on man, you're defense of your expertise is getting funny! Surely you know that neither .100" nor .001" are "tenths" of anything to a machinist. Every machinist I've ever known understands that a tenth means .0001", exactly a tenth of a thou. (And everyone knows .001" is a thou. At least I think I know that but you may have different definitions! )

  13. #53
    Boolit Master uscra112's Avatar
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    Quote Originally Posted by M-Tecs View Post
    I have to say this thread is turning into a P*****g contest.


    For gage blocks three sets of new SPI were rejected on initial cal. The replacement Starrett sets all fully passed the initial cal.
    Forgive me please, but what instrumentation did your shop have that was precise enough to "calibrate" gage blocks? What was your reference standard? Serious question, not snark.
    flectere si nequeo superos, acheronta movebo

  14. #54
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    Quote Originally Posted by M-Tecs View Post
    I have to say this thread is turning into a P*****g contest.
    See my post #39
    John
    W.TN

  15. #55
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    Quote Originally Posted by uscra112 View Post
    Forgive me please, but what instrumentation did your shop have that was precise enough to "calibrate" gage blocks? What was your reference standard? Serious question, not snark.
    Definitely a fair question. We didn't have any calibration capabilities. Everything had to be sent of to Airforce PMEL labs for initial calibration and all subsequent scheduled calibrations. Items too large to be sent out PMEL technicians would come inhouse with the necessary equipment.

    https://www.matsolutions.com/Blog/ta...libration.aspx

    What Is a Precision Measurement Equipment Laboratory (PMEL)?
    A Precision Measurement Equipment Laboratory (PMEL) is a United States Air Force (USAF) facility that calibrates and repairs test and measurement equipment. There are PMEL labs throughout the Air Force, overseen by AFMETCAL (Air Force METrology and CALibration) Program Office, located in Heath, Ohio.
    PMEL technicians are responsible for the calibration and preventative and corrective maintenance of all the avionic, navigational, radar, test and intelligence equipment used by the USAF. They maintain, calibrate and certify the equipment in coordination with AF Primary Standards Laboratory, and to the National Institute of Standards and Technology (NIST) and other AFMETCAL-approved standards.
    Last edited by M-Tecs; 05-16-2019 at 04:34 AM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  16. #56
    Boolit Master
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    We fired an apprentice once,he knew he was getting the boot,and systematically altered the setting on all the length rods for the big inside micrometers......he was smart enough not to alter shorty ones used all the time,and just did the long ones.....the first stuff up cost thousands of dollars.......unfortunately ,even a meter rule could detect the difference in the finished work.Everything had to be recalibrated.

  17. #57
    Boolit Master uscra112's Avatar
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    @M-Tecs: And that's the only answer, unless you worked at NIST or a gage block mfgr. (Or PTB in Germany.)

    For the benefit of them as might be interested: https://www.usna.edu/Users/oceano/ra...e%20blocks.pdf

    145 pages about nothing but gage blocks. Obviously well off the original topic, but interesting. Foundational tech for almost everything we do.
    Last edited by uscra112; 05-16-2019 at 06:11 AM.
    flectere si nequeo superos, acheronta movebo

  18. #58
    Boolit Master uscra112's Avatar
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    Quote Originally Posted by john.k View Post
    We fired an apprentice once,he knew he was getting the boot,and systematically altered the setting on all the length rods for the big inside micrometers......he was smart enough not to alter shorty ones used all the time,and just did the long ones.....the first stuff up cost thousands of dollars.......unfortunately ,even a meter rule could detect the difference in the finished work.Everything had to be recalibrated.
    There is a story, perhaps apocryphal, perhaps not, that alteration of standards that way was a sabotage trick used by forced laborers in Nazi arms factories.
    flectere si nequeo superos, acheronta movebo

  19. #59
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    Quote Originally Posted by uscra112 View Post
    @M-Tecs: And that's the only answer, unless you worked at NIST or a gage block mfgr. (Or PTB in Germany.)

    For the benefit of them as might be interested: https://www.usna.edu/Users/oceano/ra...e%20blocks.pdf

    145 pages about nothing but gage blocks. Obviously well off the original topic, but interesting. Foundational tech for almost everything we do.

    Before anything could be put into service it had to pass the initial calibration. I never kept track of what percent of the new unused items came back from initial cal. with limitations or outright failed but it was a surprisingly high percentage.

    Quote Originally Posted by M-Tecs View Post
    For those interested in the history of gage blocks

    https://www.nist.gov/sites/default/f...ns/mono180.pdf

    Different link but same source document as I posted above.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

  20. #60
    Boolit Master uscra112's Avatar
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    The cynic would of course say that the vendors, having won with the lowest bid, sent the Grade B stuff.

    Metrology was a large part of my engineering career. My old Dad, who was wiser than I ever gave him credit for, once said: "It's a fascinating profession, but you'll never have cocktail party conversation." (Except with other engineers, I hasten to add.)
    Last edited by uscra112; 05-16-2019 at 04:16 PM.
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