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  1. #21
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    Quote Originally Posted by Gordon B. Clarke View Post
    To all. To me there are 4 types of measurement caliper. Vernier, dial and digital. The 4th ("leg") is the type that requires another measuring instrument to "calibrate" the result.

    Might be good if what type is meant when "caliper" is mentioned.
    I call the three you enumerated first as beam type. I have too much respect for the tool to say “they look like a stillson or monkey wrench”.

    The leg type may actually be the value if that’s the only instrument you can get to something with. I’ve actually had to use a beam trammel before & then “it” was the basic reference used. Everything doesn’t always fit in a small box.

    Merry Christmas to you also,
    Matt
    Attached Thumbnails Attached Thumbnails beam_trammel.jpg  

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    Calipers have their application but i wouldn't bet my shirt on guaranteeing anything better than a couple of thou.
    Diatest sets are dirt cheap now because everyone has gone to CMMs. These are awesome for checking bores as you can "feel" the hole.
    The best lever caliper i used/had was one of these.
    Very flexible as it would check grooves too.
    https://tesatechnology.com/en-gb/pro...els_p41038.htm

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    Quote Originally Posted by barbter View Post
    Calipers have their application but i wouldn't bet my shirt on guaranteeing anything better than a couple of thou.
    Diatest sets are dirt cheap now because everyone has gone to CMMs. These are awesome for checking bores as you can "feel" the hole.
    The best lever caliper i used/had was one of these.
    Very flexible as it would check grooves too.
    https://tesatechnology.com/en-gb/pro...els_p41038.htm
    When you write "a couple of thou" are you comparing internal measurement with a caliper against a Diatest or similar?

    I suppose compared to CMMs they are "dirt cheap". I've found that the "circular" measurement movement makes them a bit "touchy feely". I prefer linear.

    My question to those that use them is what do you use as "reference"?

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    Quote Originally Posted by Gordon B. Clarke View Post
    When you write "a couple of thou" are you comparing internal measurement with a caliper against a Diatest or similar?

    I suppose compared to CMMs they are "dirt cheap". I've found that the "circular" measurement movement makes them a bit "touchy feely". I prefer linear.

    My question to those that use them is what do you use as "reference"?
    I'm talking general accuracy as a tool. We all know that calipers are a general tool and not very accurate.
    You cannot compare measuring a bore with a digital caliper compared to a diatest bore gauge.
    Chalk and cheese.

    For using a refernce, everything goes back to either a calibrated 20c ring gauge or inspection gauge blocks.
    We used to use a mic as a fiducial but set that to size with gauge blocks and lock it, then set the diatest or interapid off that.
    That's what i said in the digital mic thread with the mitutoyos...use that as a fiducial against gauge blocks but the mics would read to within a micron or so anyway. Unbelievable repeatability.

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    I am not sure what a 'diatest' is... but this is a (relatively) in-expensive kit for setting bore gages -

    https://www.mscdirect.com/product/details/92828045

    It takes a little more finesse than a ring gage as you have to sweep front to back and left to right to get the correct measurement, but nearly as accurate as your gage blocks are, if you use it properly.

    Pair with this, https://www.mscdirect.com/product/details/75128066 for under $700 ish and you can accurately measure bores from 2-6", not a bad deal IMO.

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    Quote Originally Posted by Mike1974 View Post
    I am not sure what a 'diatest' is... but this is a (relatively) in-expensive kit for setting bore gages -

    https://www.mscdirect.com/product/details/92828045

    It takes a little more finesse than a ring gage as you have to sweep front to back and left to right to get the correct measurement, but nearly as accurate as your gage blocks are, if you use it properly.

    Pair with this, https://www.mscdirect.com/product/details/75128066 for under $700 ish and you can accurately measure bores from 2-6", not a bad deal IMO.
    Here you go (attached). They're split point gauges - excellent because you can feel a bore by (gently/slowly) running the gauge up and down the bore.
    And you can see the shape of the bore too - if it's oval or internally bell shaped etc.
    I had the full sets which went from 0.5mm dia to 28mm dia.
    Also Bowers 3 probe digital, which went from 6mm to 100mm dia. These are excellent, but just an on/off type measurement, but no comparison against the Diatest.
    All bought used (but excellent condition) for a fraction of the new price - and if measuring to less than 10 microns, I'd put my house on the actual sizes compared to a CMM result.

    Also had both sizes of Diatest CSK gauges - so when setting up on the machine, we could check and adjust tool length easy peasy.
    As I said, great (actually exceptional) kit, available at cheap prices because QA managers have removed them from their system because they now have a CMM which does everything LoL
    Attached Thumbnails Attached Thumbnails diatest-bore.jpg   diatest-chamf.jpg  

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    Quote Originally Posted by Gordon B. Clarke View Post
    This is a relatively old thread revived again. I suppose I'll never understand why calipers (and I personally prefer digital) seem to create so much difference of opinion.

    I can't think of a more inexpensive, versatile measuring tool. Outside, inside and depth. As far as accuracy goes then it's a question of what you use it for. If a standard 150mm / 6" digital caliper isn't accurate when measuring external to within 0.03mm / 0001" then you have a defect caliper.

    Feel is very important and measuring blindfolded is ridiculous. I check my calipers now and then against something I know the measurement of. Small ball bearings are handy to have.

    I have the feeling many still have old calipers or buy second hand. I'm lucky in that mine are all relatively new. Of course I have and use micrometers (outside and inside) and dial indicators. It all comes down to what I want to measure and how accurately I need to measure.

    YouTube

    I'll also just add:

    A VERY MERRY CHRISTMAS TO ONE AND ALL.

    Gordon- didn’t you accidentally slip an extra zero in the above?? .03mm is about a thousandth of an inch not one tenth thousandth .


    Sent from my iPhone using Tapatalk Pro

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    Quote Originally Posted by ripperj View Post
    Gordon- didn’t you accidentally slip an extra zero in the above?? .03mm is about a thousandth of an inch not one tenth thousandth .
    I'm glad you realized it was a mistake on my part and not lousy maths

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    Quote Originally Posted by barbter View Post
    I'm talking general accuracy as a tool. We all know that calipers are a general tool and not very accurate.
    You cannot compare measuring a bore with a digital caliper compared to a diatest bore gauge.
    Chalk and cheese.

    For using a refernce, everything goes back to either a calibrated 20c ring gauge or inspection gauge blocks.
    We used to use a mic as a fiducial but set that to size with gauge blocks and lock it, then set the diatest or interapid off that.
    That's what i said in the digital mic thread with the mitutoyos...use that as a fiducial against gauge blocks but the mics would read to within a micron or so anyway. Unbelievable repeatability.
    Accuracy is achieved by using something that is relevant to the dimension and tolerance being measured. Same as a car from getting you from A to B and back. All are made to do that but some cost a wee bit more (major understatement) than others.

    Internal measuring tools like the Diatest require a reference for calibration. That's not cheap but often overlooked when giving a price. Bit like a car with an empty tank.

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    indicating bore gages i often set using gage blocks when i dont have a ring gage. obviously need gage block accessories or ends and the connecting screws and tubing and to compensate for error on the blocks
    .
    cheaper indicating bore gage sets are often <$100. and set has a considerable size range. sure they come in like small, medium, large size sets

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    Normally I would not trust calipers or telescopes to .0005.
    Digital calipers are a wonder for for the accuracy they provide and the range perhaps 6,8 12 inches. Even the low end name brands are highly accurate...
    Only draw back is needing batteries (so I keep my old verniers just for backup)

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    One thing is for certain, if you don’t have confidence and some proper practice nothing is going to work well for you. I’m not so “skippy” with gage pins either without practicing a bit to get the routine down. Removing stuck things from a bore sucks rocks...

    I was able last year to easily determine go-nogo on a .360-.3605” pair of gage block stackups with a flat bottom ball gage responding to measuring a very shallow depth bore question in the metrology forum, mic-ing them was more uncertain. I didn’t do so well with centering snap gage or a spring caliper going inside of .001”. But I didn’t really spend that much time at it (just curiosity).

    I’m don’t want to be the mouse wandering around while a hawk is flying overhead so anything handy might be a plan B. Attached is the junk I played with trying that 5 tenth nonsense & another 3 that describe the “point gage bore sizing” with the math needed. On the latter if you double the .012mm behind the 375mm → it’s pretty impressive, hell of a routine that...

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails test_3605_slot2.jpg   test_3605_slot.jpg   measure_bore_pointgage_p28.jpg   measure_bore_pointgage_p29.jpg   measure_bore_pointgage_p30.jpg  


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    This is mainly for barbter. I have 2 delete options.

    1. I can completely delete a post as if it had never been written.

    2. I can delete and save in case it's needed at some point in time as to why it was deleted.

    With your posts I go for option 2.

    Some of your posts are informative and that's good. When they become insulting and/or provocative they will be deleted. If you can't help yourself then just go elsewhere to post.

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    Returning to topic, I may well pickup an indicating bore gage. Given that I won't likely be using it often I'm considering that it may well be suitable to either clamp together gauge blocks or to use a micrometer for setting the bore gauge. Assuming the gauge blocks are probably the better of those two methods since one could sweep through a set of gauge blocks book ended with setup blocks.

    Hopefully you all aren't picturing a c-clamp keeping this together, I have small brass clamps for delicate clamping operations.

    I had thought to simply use snap gauges, but I'm concerned that there are two many sources of potential error in that getup for measuring .0005". I recall at the machine shop I worked in, we really only ever used snap gauges if the bore was in an awkward location. Outside of that we typically used an indicating bore gauge.

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    Don't forget Abbe's law - "In order to improve measurement accuracy, the measurement target and the scale of the measuring instrument must be placed in a collinear fashion in the measurement direction." This is a primary reason that calipers are less accurate than micrometers.

    We have used Dialtest gages and have not had great results. Instead of Dialtest we now use tri-mics. The smallest bore we tend to measure is about 1/4".

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    Quote Originally Posted by markz528 View Post
    Don't forget Abbe's law - "In order to improve measurement accuracy, the measurement target and the scale of the measuring instrument must be placed in a collinear fashion in the measurement direction."
    1. This is a primary reason that calipers are less accurate than micrometers.

    We have used Dialtest gages and have not had great results.
    2. Instead of Dialtest we now use tri-mics. The smallest bore we tend to measure is about 1/4".
    In the hope of a "friendly" discussion

    ad 1. With that logic then the depth rod on a caliper should be more accurate than it is.
    To me the main source of measurement inaccuracy of a caliper is the user.

    N.B. The specified manufacturing accuracy tolerance difference for a (beam) caliper and a micrometer is at least a factor 5. I always like to see the manufacturing accuracy stated for a measuring instrument. Easy then to check before use. I know several companies that have everything lab calibrated before use. A calibration lab needs to know what specifications they're checking to or they can't state "good" or "bad".

    ad 2. I agree that a 3 point internal micrometer doesn't require the degree of "feel" a 2 point instrument does but when using a 3 point it is assumed the hole is round.

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    Quote Originally Posted by markz528 View Post
    Don't forget Abbe's law - "In order to improve measurement accuracy, the measurement target and the scale of the measuring instrument must be placed in a collinear fashion in the measurement direction." This is a primary reason that calipers are less accurate than micrometers.

    We have used Dialtest gages and have not had great results. Instead of Dialtest we now use tri-mics. The smallest bore we tend to measure is about 1/4".
    I couldn't really say a tri-mic is more accurate or not than a diatest (bore gage), but I do know they are ALOT more expensive. If you get a bore gage with a tenth indicator, and some ring gages, or a master setting gage, you can cover alot of range for a fraction of the price of tri-mics. However, if maybe you are doing a .6771" bore all day, day in and out for a production job, I could certainly see investing in an appropriate size tri-mic as it is direct reading...

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    In the post I deleted by barbter he included this link.

    https://www.mitutoyo.com/wp-content/.../07/15003A.pdf

    Interesting although not really relevant to this thread title. I don't disagree with stated accuracy. What does often get overlooked (and isn't mentioned in the link) is that measurement repeatability accuracy on a dial or digital caliper is normally 0.01mm/0.0005". IOW if a reference item with a known length or diameter is used and comparative measurement carried out then better accuracy can be achieved. Please note I write "can" and not "will be".

    I don't know if anyone can verify or not but it seems to be more "Mitutoyo" than what I've seen in international standards. The reason I write this is that in the Mitutoyo brochures I have many calipers have an international caliper manufacturing standard (that includes accuracy) given.

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    I use inside calipers for portable line boring because it is one of the few ways to get around the bar .. it takes some practice and feel to get it dialed.. and is not a quick way of measuring. I prefer dial bores for all the reason already covered. I find an inside mic is a must have tool for measuring test cuts, but that is all i use it for as its a pain to check for bell mouth/oval,etc. That said telescopic's take some practice are also easier to get used to and can be accurate, .0005 imo. Handy for quality control on a part with multiple bore sizes.

    It also depends on what size bores we are talking about..

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    It took some scraped part but once you get a feel for telescopic gages you can get repeatable measurements. It not only the feel inside the bore, it also measuring the telescopic bars. There are 2 chances for you to make a mistake. In my case I prefer to use micrometer, it an old B&S with the friction barrel. It easy to check the micrometer against gage block or pins. It bit slower to measure, because your reading the barrel in 2 places. I prefer them over my Mitutoyo digitals.


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