When using measuring tools, how much force is used to press against the part?
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    Default When using measuring tools, how much force is used to press against the part?

    I have been trying to get into the machining. When using calipers or other similar measuring tools, when do I stop pressing together to get the correct measurement?

    When you press harder, it will measure smaller amounts, but I am sure at some point it is bending the tool or something.

    Seems like I can get a wide variety of readings and when I purchase new tools, I would like to make sure I dont mess them up by using them improperly, and keep them calibrated.

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    Quote Originally Posted by MetalArtistCandy View Post
    I have been trying to get into the machining. When using calipers or other similar measuring tools, when do I stop pressing together to get the correct measurement?

    When you press harder, it will measure smaller amounts, but I am sure at some point it is bending the tool or something.

    Seems like I can get a wide variety of readings and when I purchase new tools, I would like to make sure I dont mess them up by using them improperly, and keep them calibrated.
    Some time take a look at the back end of a micrometer. They have either a friction or ratchet thimble to prevent excess force. In the case of a micrometer it's probably as much to protect the delicate precision screw but if you apply enough force to calipers they can flex enough to alter readings.

    The faces of the measuring instrument (and the work) should be clean and then presented squarely to the work with just enough pressure to be sure they are in contact.

    There are special pressure sensing calipers. A PM poster sells some, but for day to day use cleanliness and some experience will see most machinists through. Calipers are semi precision tools. Micrometers are more accurate.

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    Use gauge blocks and ring gauges to "calibrate" your feel.

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    Cheap sloppy calipers will make it difficult to get an accurate measurement. Buy the good stuff.

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    If you have set the gap on a spark plug you would get a feel for what a fit is. You are not trying to clamp the mic jaws to your measurement piece, barely sliding contact.

    Another good thing is to get a piece of paper, envelope, business card and squeeze the jaws on gently, then pull out. Look up close with a lens on the jaws and you may see a lot particles. I use a small tooth brush for the big clean.

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    I've seen people make mics read .001 off to "hit" a dimension on the print.
    Caliper....measuring force....
    Gordon...Gordon...Gordon....
    Bueller Bueller Bueller - YouTube

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    I recall many years ago(~40) Starrett had a high precision c-frame mike that would set to a calibrated force. The thimble was huge. I don't know what the part number was and have not seen one since. Perhaps some of OF's will recall this.

    Tom

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    If you can't get a one or two tenth(thousandth) feel in a week of measuring Jo block then the machine trade likely is not for you..

    The friction and/or click device should give the same good results..

    Also need to get used to feel the part with locking the lock and feel how the part feels through at different places..

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    If you press on the jaws of a caliper, directly in line with the workpiece, no bending is possible and the results will be very repeatable. The zero should be set the same way.

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    Quote Originally Posted by greif1 View Post
    If you press on the jaws of a caliper, directly in line with the workpiece, no bending is possible and the results will be very repeatable. The zero should be set the same way.
    I've seen how caliper manufacturers and calibration labs calibrate calipers. Neither do as you write.

    "Bending" is always possible depending on how much force is used and where the calibration item is with regard to the caliper beam.

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    Measure a jo block with not looking .. then look at the numbers to see they match the JoBlock... Set the numbers two tenth loose..a half thousandth tight , then a half loose (yes don'r force and damage you measuring device..)set one thosandths loose and look at the space with a lop or just a good light. Then set .003, .005 .010 and look (and feel) at the space. Check round and flat parts..Measure a step or a shoulder length with using a loop and being off the part..then check the same with a JoBlock and an indicator..

    Yes this would/could be good practice for an apprentice..perhaps an apprentice test.

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    Measuring is not really rocket science until a person gets into tenths. I always tell people that the human eye under the right situation can likely see a thousands; I know I can see one of my .003" thick/thin hairs laying on a sheet of paper so not unreasonable to imagine .001"? I worked with a fellow that used to get stuck re-single pointing precision aircraft threads that were rejected by inspection, all he had to go by when setting it up was looking at the light coming through on both sides of the tool. Some of those parts were for fighter jet landing gear and extremely expensive and there wasn't much excess material so no room for error.
    If .001" is the type of tolerance your shooting for simply practice with a set of feeler gages, what is important is getting s feel for the work that is repeatable every time.
    Dan

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    Quote Originally Posted by Gordon B. Clarke View Post
    I've seen how caliper manufacturers and calibration labs calibrate calipers. Neither do as you write.
    I too press directly on the jaws to eliminate error.

    Cal labs certainly do use this technique. That's where I learned it.

    A caliper must have clearance to permit free movement of the beam. If pressure is placed on the jaws using the beam, that clearance creates an undefined error.

    You can quantify that error either by observation or mathematically.

    -Leigh

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    Quote Originally Posted by The real Leigh View Post
    I too press directly on the jaws to eliminate error.

    Cal labs certainly do use this technique. That's where I learned it.

    A caliper must have clearance to permit free movement of the beam. If pressure is placed on the jaws using the beam, that clearance creates an undefined error.

    You can quantify that error either by observation or mathematically.

    -Leigh
    I also press directly on jaws if I am working with calipers of guestinable quality.
    But in dimension cal lab where I worked ages ago all the calipers that needed tricks like that went to scrap bin..

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    Quote Originally Posted by MattiJ View Post
    I also press directly on jaws if I am working with calipers of guestinable quality.
    But in dimension cal lab where I worked ages ago all the calipers that needed tricks like that went to scrap bin..
    It appears they don't teach laws of physics and mechanical design in Finland.

    - Leigh

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    Quote Originally Posted by The real Leigh View Post
    It appears they don't teach laws of physics and mechanical design in Finland.

    - Leigh
    Manufacturers like Mitutoyo suggest measuring as deep as possible in the jaws as possible (same physical principle as noted above). That said, the ID jaws and the knife edge OD jaws are often needed. Makes good sense for a calibration lab to take those out of service rather than have shop floor folks perform their interpretation of QC tricks and techniques.

    Meanwhile, seems it's the US that isn't teaching math and science, at least compared to Finland: Rankings Of Countries In Math And Science - Business Insider

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    Quote Originally Posted by The real Leigh View Post
    It appears they don't teach laws of physics and mechanical design in Finland.

    - Leigh
    This is because based off of your posting history, you are in fact a skilled craftsman...Gordon Clarke, based off his history...not at all.

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    I think Gordon lives in Denmark

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    As a practical note with respect to the OP, note that a good pair of calipers (with a certified calibration report) repeatability and resolution are 0.0005" each, or +/-.001 accuracy, and Chinese Specials, who knows. So don't really expect any better Cheepos will (likely) have error in the mechanical parts and the jaws not parallel or stable resulting in more variation, especially under varied use of the caliper.

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    Quote Originally Posted by The real Leigh View Post
    I too press directly on the jaws to eliminate error.

    Cal labs certainly do use this technique. That's where I learned it.

    A caliper must have clearance to permit free movement of the beam. If pressure is placed on the jaws using the beam, that clearance creates an undefined error.

    You can quantify that error either by observation or mathematically.

    -Leigh
    I stand by by my many personal observations.


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