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Thread: Two Micrometers Don't Agree

  1. #1
    Boolit Master

    alamogunr's Avatar
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    Two Micrometers Don't Agree

    I hope there are several machinists here that might know what I can do about the problem in the title. I have two 0-1" micrometers, a Brown & Sharpe and a Schure-Tumico(sp?) that differ when checking against a .310 plug guage. Both zero out when closed on the anvil but differ by .0004 when I measure the plug guage. The B&S measures exactly .3100. The Schure-Tumico measures .3096. Both have a vernier for the 4th place. I have cleaned both measuring surfaces but don't know what else to do.

    1. Is there any adjustment that would make both measure the same?

    2. Is that difference meaningful in reloading/casting?
    John
    W.TN

  2. #2
    Boolit Grand Master



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    Two separate issues.

    First what is the tolerance of your plug gage? If it is .3100" gage pin it will be a specific class with a plus or minus tolerance. If it's a ZZ class the tolerance is .0002".

    While it is correct that a plus .3100" could be anywhere for .3100" to .3102" the actual size will be very close to 3102". On a minus gage (which is the most commonly purchased) the actual size will be very close to the .3098" . Ring gauges will be just the opposite. This does hold true for quality name brand gages. Not sure about the cheaper imports. I have to say though, I have never measured a pin that wasn't .0002" under nominal for a minus pin or .0002" over for a plus pin.

    Second when both zero at close but read different at .3100" one or both have wear or a manufacturing error. Using an actual standard or gage block you can zero it for a specific size but it will be off at other sizes.

    https://www.threadcheck.com/technica...sheet-pg28.pdf
    Last edited by M-Tecs; 05-03-2019 at 10:06 PM. Reason: corrected info.
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  3. #3
    Boolit Grand Master
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    Two Micrometers Don't Agree

    One of them is wrong

  4. #4
    Boolit Buddy Jedman's Avatar
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    For any reloading or casting situation I can't even think of anywhere that .0004 would be meaningful.

    Jedman

  5. #5
    Boolit Buddy
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    Quote Originally Posted by alamogunr View Post
    I hope there are several machinists here that might know what I can do about the problem in the title. I have two 0-1" micrometers, a Brown & Sharpe and a Schure-Tumico(sp?) that differ when checking against a .310 plug guage. Both zero out when closed on the anvil but differ by .0004 when I measure the plug guage. The B&S measures exactly .3100. The Schure-Tumico measures .3096. Both have a vernier for the 4th place. I have cleaned both measuring surfaces but don't know what else to do.

    1. Is there any adjustment that would make both measure the same?

    2. Is that difference meaningful in reloading/casting?
    Yes, remove the spindle, there's a tapered/threaded nut over slots in the shaft.
    Tightening it removes any play/excessive clearance in the threads.
    good luck,
    I will never accuse anyone of providing TOO MUCH information

  6. #6
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    "Two Micrometers Don't Agree
    I hope there are several machinists here that might know what I can do about the problem in the title. "

    from the headline and first line I was thinking they are both female. Solution no man knows
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  7. #7
    Boolit Grand Master

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    What I suspect is an out of square anvil on the second set. wear or otherwise. If you have pin gages check them at every 1/4 turn of the spindle. ( A mic makes .025 per revolution so every .006) This will show the out of square in the anvil. Another issue I've seen in production tooling that gets used a lot in one spot or range is localized wear. We had mics used in production that 24/5 measured dias of the same size. after a few years wear would affect accuracy at that range and they would be moved to a different line and size range. The localized wear couldn't be adjusted out with the adjustment collet since it would make it to tight on either side of the wear. By moving them from line to line and keeping wear more even they could be lapped and readjusted. Another quick test is to use 2 pieces of shim stock the same thickness and close mics to feel and check size then try and slide each piece seeing if one side is looser repeat 90*. When checking for square use pins .xx0, .xx6, .x12, .x18. we also checked thru the full range of travel

    Mics can wear from use grinding and some processes are harder on the faces than others. Can have frames sprung from heavy handed use or being dropped. Wear in the threads from much use in the same range. Another effect is heat temp and frame materials some materials don't expand as much others more some mics have plastic shields to limit body temps from frames.

    On 0-1" close the anvils lightly on a cigarette paper and slide out this cleans the anvils do this a couple times then check zero. The paper will show any dirt or crud removed. Last is to disassemble and clean with fresh new solvent flushing and very gently swabbing with soft utensils. blow dry with low pressure air lightly oil with a good insterment oil and reassemble carefully. After this they will need to be re zeroed and set.

  8. #8
    Boolit Grand Master
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    Quote Originally Posted by Smoke4320 View Post
    "Two Micrometers Don't Agree
    I hope there are several machinists here that might know what I can do about the problem in the title. "

    from the headline and first line I was thinking they are both female. Solution no man knows

  9. #9
    Boolit Master

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    Quote Originally Posted by M-Tecs View Post
    Two separate issues.

    First what is the tolerance of your plug gage? If it is .3100" gage pin it will be a specific class with a plus or minus tolerance. If it's a ZZ class the tolerance is .0002".

    While it is correct that a plus .3100" could be anywhere for .3100" to .3102" the actual size will be very close to 3102". On a minus gage (which is the most commonly purchased) the actual size will be very close to the .3100" to allow for wear and still be in size. Ring gauges will be just the opposite. This does hold true for quality name brand gages. Not sure about the cheaper imports.

    Second when both zero at close but read different at .3100" one or both have wear or a manufacturing error. Using an actual standard or gage block you can zero it for a specific size but it will than be off at other sizes.

    https://www.threadcheck.com/technica...sheet-pg28.pdf
    I bought the set of pin guages on Ebay. It is a Meyer minus set and I have to assume that it is ZZ tolerance since there isn't any indication on the box. I think I got it cheap because it was listed as having several pins missing. When I got it, the missing pins were not ones that I was likely to need.

    I will measure several pin sizes in the range(.250-.750) of the micrometer and see how the different measurements compare. If the measurements are within the range of the first comparison, I think I will just accept whatever the reading is. As Jedman said, I don't think that difference would be meaningful.
    John
    W.TN

  10. #10
    Boolit Master
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    If you have gage blocks, gage pins, or other items you can uses as standards, check them at different sizes. See if the difference is .0004" at any size or if it changes.
    If .0004" is constant at any size it probably won't ever be much of a problem.
    If it doubles at .620 and triples at .930, at least it' a linear error; it's predictable.
    If it's all over the place as you measure different sizes the mic is probably damaged or dirty inside.
    Warning: I know Judo. If you force me to prove it I'll shoot you.

  11. #11
    DOR RED BEAR's Avatar
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    I would have to say wear or manufacture error as stated above could also be from someone that didn't know how to use a mic and tried to use it as a c clamp. I got to the point where i refused to allow anyone to use my tools. Just got tired of replacing them.

  12. #12
    AKA: GRMPS Conditor22's Avatar
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    Some brands you can take apart and clean the contact area. Not familiar with those 2 brands

  13. #13
    Boolit Master

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    One of the two is a democrat micrometer, that one is lying to you.
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    I am a sovereign individual, accountable
    only to God and my own conscience.

  14. #14
    Boolit Master

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    As pointed out by CG, face wear on the anvil is not unusual, especially with steel faces, carbide less so. Probably just need cleaned and re-calibrated. A standard or gage block will be much more precise than a plus/minus plug gage.
    Before you embark on a journey of revenge, dig two graves.

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  15. #15
    Boolit Master
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    It seems that possibly both micrometers are having problems.
    A .310 minus pin should be about .3098 meaning one of your mikes is over and one is under.

    Rather than compare the 2 mikes I would pick one and remove the spindle, clean out both male and female threads and lubricate and re-assemble. Check again then adjust the clearance in the female thread and check again. You might be able to improve the reading by adjustment. If not pick where you want the error to be minimized and adjust your zero to put the mike error on the other end of the measurement range.

    I collect mostly high end mikes and at one time supervised 2 different calibration labs.
    I have both B&S as well as STI mikes and have never bought a mike off of Ebay with more than about .0001 error end to end. Most read exactly right end to end. I will add that most mikes I buy are based on higher quality brands that appear to be in excellent condition so I expect them to be right. I have bought a number of clunkers and was surprised to find they are still accurate even when beat up and ugly.
    I have no idea why you mikes would be off considering the following.
    I bought 3 mikes in a lot on Ebay $9 expecting junk.
    1. Well used Slocomb 1-2 inch mike missing half the paint. The mike is probably 60 or 70 years old.
    It still had the anti-backlash device though it was not installed correctly. This mike was cleaned up and works perfectly.
    2. A Reed Small Tool Works 0-1 mike - the worst rust pitted mike I have ever worked on. Looks horrible. Works perfect and reads correctly end to end. This mike might be 70 years old and is one of the predecessor brands that is now Scherr Tumico.
    3. Starrett #238 This mike was the reason for buying the lot. This is a super heavy duty boat anchor of a mike that is about 75 or 80 years old. It has seen very heavy use over many decades and has no original finish left. It needed a little cleaning and it reads as close as any mike I have ever used.

    If your mikes appear to be in good condition I could not guess why they would be off. There is just not much chance for error in the spindle threads.
    My most used mikes were about 20 to 30 years old when I bought them more than 50 years ago. In spite of constant use they check out perfectly end to end every time I check them out. Though I worked with calibration personnel a good bit I never let them touch my personal tools.



    Quote Originally Posted by alamogunr View Post
    I bought the set of pin guages on Ebay. It is a Meyer minus set and I have to assume that it is ZZ tolerance since there isn't any indication on the box. I think I got it cheap because it was listed as having several pins missing. When I got it, the missing pins were not ones that I was likely to need.

    I will measure several pin sizes in the range(.250-.750) of the micrometer and see how the different measurements compare. If the measurements are within the range of the first comparison, I think I will just accept whatever the reading is. As Jedman said, I don't think that difference would be meaningful.
    Last edited by EDG; 05-03-2019 at 09:00 PM.
    EDG

  16. #16
    DOR RED BEAR's Avatar
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    I will say in my opinion there is not a better mic than brown and sharpe. Starret makes a good mic but brown and sharpe always had a better feel.to me.

  17. #17
    Boolit Grand Master



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    Quote Originally Posted by EDG View Post
    A .310 minus pin should be about .3098 meaning one of your mikes is over and one is under.

    I collect mostly high end mikes and at one time supervised 2 different calibration labs.
    Per my experience I have never measured a pin that wasn't .0002" under nominal for a minus pin or .0002" over for a plus for a ZZ class pin. That is what I always believed based on my experience and that is what I have always posted.

    I did post this on another forum awhile back and a gentlemen claiming to run a Metrology lab ripped me a new one claiming that with a minus gage pin the actual size will be very close to nominal to allow for wear and still be in size. With his claim a .3100" that would allow for .0002" pin wear and still be intolerance. Sounded logical enough that he convinced me that I was wrong. After your post and a little research I can not find any support for his claims. From 1982 to 1994 I worked for a company that had 4 full time Metrologists for inhouse calibration. From 1994 till 2016 I sent everything out for calibration so have I am far from an subject matter expert on Metrology.

    Based on your comment, my experience and what I can find on the web I edited my above post. When you supervised calibration labs did you ever see anything to support his claim that minus pins would be closest to nominal to allow for pin wear?
    Last edited by M-Tecs; 05-03-2019 at 10:03 PM.
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  18. #18
    Boolit Master
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    I agree with your experience. The centerless grinders use almost none of the tolerance. The .0002 undersize pins are always exactly .0002 under in my experience. The undersize is intended to permit the pin to be a slip fit in an exactly nominal hole.
    The only time I have seen minus pins vary from that is when a tool maker polished one further undersize for some specific reason or when the shop people just wore out certain pins. The pins do wear when heavily used but when replacements are only $3 each it is easy enough to keep full set of good pins. The shops I worked in built a lot of military equipment held together with #4, #6 and #8 fasteners. The pins that were used to gauge the common tap drill diameters got used up pretty fast and had to be replaced regularly. So the guys inspecting the parts had a separate set of pins. Instead of the pins being used to check the mikes. the mikes were always checked to zero and with gage blocks. The mikes were used to verify the pins were what they said they were.

    Quote Originally Posted by M-Tecs View Post
    Per my experience I have never measured a pin that wasn't .0002" under nominal for a minus pin or .0002" over for a plus for a ZZ class pin. That is what I always believed based on my experience and that is what I have always posted.

    I did post this on another forum awhile back and a gentlemen claiming to run a Metrology lab ripped me a new one claiming that with a minus gage pin the actual size will be very close to nominal to allow for wear and still be in size. With his claim a .3100" that would allow for .0002" pin wear and still be intolerance. Sounded logical enough that he convinced me that I was wrong. After your post and a little research I can not find any support for his claims. From 1982 to 1994 I worked for a company that had 4 full time Metrologists for inhouse calibration. From 1994 till 2016 I sent everything out for calibration so have I am far from an subject matter expert on Metrology.

    Based on your comment, my experience and what I can find on the web I edited my above post. When you supervised calibration labs did you ever see anything to support his claim that minus pins would be closest to nominal to allow for pin wear?
    EDG

  19. #19
    Boolit Master
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    Could be how you use your mike.
    Some clickers on the end are harder set and some people tend to jack hammer a mike to get what reading they want to.

    Only thing I could add to the excellent posts above is to pick one and just use that for the job at hand.
    Changing measuring tools while working adds in more tolerance errors.

    Different if you need to order something to the half a hair on a knats knacker I guess thou.

    Then again you may need a set of mikes like mine.

    Click image for larger version. 

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    Can only be found in classy machine shops.

    Since we are talking about such things.
    Last edited by barrabruce; 05-04-2019 at 12:56 AM.

  20. #20
    Boolit Master
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    There are a number of very good to excellent brands.
    Using many different brands taught me an important lesson.
    Most decent brand name mikes will measure your work accurately.
    The real difference that really become noticeable is the ease of seeing and reading the mike.
    The satin chrome finished Brown & Sharpe mikes with black ink filled lines and numerals are among the easiest to see and read.
    If you are in a location where the light source is behind your back it can be very difficult to see the lines on the barrel and thimble on some mikes. Natural steel with a smooth bright reflective surface is a terrible finish for the thimble and barrel. In good light you get a bright reflection back into your eyes.



    Quote Originally Posted by RED BEAR View Post
    I will say in my opinion there is not a better mic than brown and sharpe. Starret makes a good mic but brown and sharpe always had a better feel.to me.
    EDG

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