Inside caliper vs telescoping gauges
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    Default Inside caliper vs telescoping gauges

    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!

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    I have used both. With an inside mike you are feeling for the loosest position (diameter) in one direction and the tightest in the other (longitudinal). It takes practice to get the "feel" for getting the reading. With telescoping gauges the user just sweeps the gauge through the bore. The gauge picks up the diameter without the need for "feel". Telescoping gauges are a lot more convenient than inside mikes.

    That is probably not a clear expkanation. If you use the mike and then use telescoping gauge you will notice the difference.

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    Calipers in general for linear measurements are only good for +/-.001 (if you're careful), when measuring an ID it becomes even less accurate because of variability of placement of the caliper. And you can't really place a caliper "in" the bore to take a measurement, just at the top of a bore. The width of the caliper blade has a large error as the holes get smaller. You can get about the accuracy of the caliper on larger holes (with care), with a telescoping gage and micrometers (not caliper), and care, you can get within approx +/- .0003 . I use them even with the calipers (versus micrometers) for any hole that requires better than +/- .005 or so, and use mics and the gages for less than .003 required.

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    Are we talking inside jaws of a digital caliper or an old school inside caliper?

    The former won't reach very far into a bore, are fragile, and don't have a good sense of feel. They are quick.

    The latter typically don't have well finished ends and are harder to "sweep" than a telescoping gage. The t-gage handle also helps with reach and perpendicularity. In addition, a telescoping gage locks for subsequent micrometer measurement, while the caliper needs to be sort of swept again against the mic anvils.

    That said, either type of calipers might get you within a couple thousandths.

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    Quote Originally Posted by pugglewuggle View Post
    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!
    I think we all know what telescoping gauges are but not so sure about inside calipers. The picture is what I call an inside caliper.

    Which is better/more accurate? It all depends on use. To use telescoping gauges you also need a micrometer, in fact 6 if you want to cover the range up to 6"/150mm. Takes longer time too to measure with telescoping gauges.

    Personally, when I use a caliper (inside or standard) to measure internally, the first thing I do is to calibrate it against a ring with a known ID. Closing it and zeroing it just isn't good enough. I zero on the known hole diameter and add that onto the measurement result I get from the hole measurement. I'd feel confident of getting a result within 0.02mm/0.001". Maybe even less.

    As to telescoping gauges then it'll very much depend on who's using them and their experience with them.

    Now if what I've shown isn't what you mean by "inside caliper" then you'd better tell us what you do mean.

    ic.jpg
    Last edited by Gordon B. Clarke; 12-09-2018 at 04:49 AM.

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    Quote Originally Posted by pugglewuggle View Post
    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!
    First reason: "reach". Second reason: "minimum size". Third reason: "accuracy". Fourth reason: Odd shape of a bore and/or its SUB features to be measured.

    One has to have "all of".. gage pins, telescoping gages, inside mics, inside calipers, bore gages, and now and then even spring calipers to get around obstructions or Indicals or similar goods for internal grooves.

    Each have advantages and disadvantages.

    Like it or not, if you can only have ONE, it would be the ancient spring caliper.. and good OUTSIDE mics with reliable setting standards to transfer to/from. PITA, but the most universally usable.

    Tedious - DAMHIKT! It is actually all I DID have for a short while.

    But VERY short, that while was to be .... before I started adding.. "all of the above".

    Inside thread mics still "to do", but not much else has been missed-out.

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    I mean an old school inside spring caliper that looks like dividers. Starrett 274-6, for example.

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    Quote Originally Posted by pugglewuggle View Post
    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!
    .
    usually use neither. a bore indicator gage can reach in much farther and easily detect bore taper and out of round (if bore is vertical)
    .
    usually set to a ring gage, or to gage blocks

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    The design of the spring calipers goes back to when a shaft and bore were made to fit each other- not made to any measured standard. If you have enough time to make repeated adjustments and measurements, and develop a good "feel" for them I suspect you could get by with them in a home shop. But getting by is all you will be doing, and wasting time doing it.

    Measuring tools is not the place to try and save money. They will cost you in time and material, lead to frustration, and suck the joy out of you.
    Last edited by J_R_Thiele; 12-15-2018 at 09:33 PM. Reason: corrected link

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    Rather than answer your question directly. I'll tell you how to measure anything. Never do it once. Always do it multiple times until your repeatability gives you confidence that your reading is correct. That is the ONLY correct procedure. Now, whatever tool provides you with that level of confidence is the right one. The rest is personal preference. Remember, these tools were made to satisfy a requirement. Just because you have not found the need for the tool does not mean the requirement doesn't exist. It just means you have not been in the trade long enough.

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    Quote Originally Posted by steve-l View Post
    Rather than answer your question directly. I'll tell you how to measure anything. Never do it once. Always do it multiple times until your repeatability gives you confidence that your reading is correct. That is the ONLY correct procedure. Now, whatever tool provides you with that level of confidence is the right one. The rest is personal preference. Remember, these tools were made to satisfy a requirement. Just because you have not found the need for the tool does not mean the requirement doesn't exist. It just means you have not been in the trade long enough.
    It's not that I disagree with you so much as I'd probably express it differently.

    Measuring multiple times and getting the same result only means you are consistent. It doesn't mean you are getting a correct measurement result.

    Probably the same as calibrating anything and using something you know the exact measurement of. As long as there is user influence involved you'll go for the "desired" measurement.

    Rarely done but much better to measure an "unknown" dimension, write down what you get and then measure with something you know will give you an accurate result. First then will you know how good you are and how good what you intend using is.

    When I claim to measure this and that and state the accuracy I get it's never done based on using just one measuring device. When I read in PM now and then how accurately some say they measure I often wonder if it is accuracy or repeatability they've achieved. Of course without repeatability no accuracy.

    It might just be said I'm calibrating myself too

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    Quote Originally Posted by pugglewuggle View Post
    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!
    I don't think calipers are as accurate as telescoping gauges measured with a good set of mics. As with anything else using them takes practice. I took some master set rings and measured them over and over to have a comparison between what I measured them at to the actual size of the ring. It's how much you tighten the lock screw that causes the most variation in measurements. I think you should buy both, I did and haven't regretted it.

    Brent

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    Quote Originally Posted by yardbird View Post
    I don't think calipers are as accurate as telescoping gauges measured with a good set of mics. As with anything else using them takes practice. I took some master set rings and measured them over and over to have a comparison between what I measured them at to the actual size of the ring. It's how much you tighten the lock screw that causes the most variation in measurements. I think you should buy both, I did and haven't regretted it.

    Brent
    .
    40 years machining and maybe used telescoping gages for maybe 2 hours compared to using indicating bore gages maybe 2000 hours
    .
    just saying indicating bore gages will easy see taper and out of round literally in seconds. never seen a professional even bother with telescoping gages.
    .
    and obviously 99.999% of professional wouldnt bother with the caliper either unless tolerance was over .002" , sure you occasionally find the guy who says he can measure .001" with his $20. calipers....... obviously he aint making many expensive parts. if you got $20,000 part with a oversize bore it can be a very expensive rework job

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    Quote Originally Posted by pugglewuggle View Post
    Hi,

    It seems that a good quality inside caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?

    Thanks!
    Simple mechanics.
    An inside mic, or telescope gauge detect contact in a single 'line' or axis of the item. That includes whatever tolerance or imperfections are contained in the tool. A good hand should/ could get near identical readings blindfolded.

    A caliper has contact points far from the frame they slide on, which requires clearance to move. The only plus to calipers is quickness, not accuracy, and can be compact compared to same size micrometer. Why digital calipers display .0005 is beyond me, other than interpreting something different than what they display seconds before. That is neither true resolution or accuracy. Regarding bores or OD's, those are always subject to interpreting squareness to axis being checked. Try that blindfolded?

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    Since this got bumped. Ignoring bore depth and range how does something like a Starrett 700A compared to telescopic gages and tubular inside mics for accuracy? I don’t trust mine to less than a thou or two.

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    Quote Originally Posted by DMF_TomB View Post
    .
    40 years machining and maybe used telescoping gages for maybe 2 hours compared to using indicating bore gages maybe 2000 hours
    .
    just saying indicating bore gages will easy see taper and out of round literally in seconds. never seen a professional even bother with telescoping gages.
    .
    and obviously 99.999% of professional wouldnt bother with the caliper either unless tolerance was over .002" , sure you occasionally find the guy who says he can measure .001" with his $20. calipers....... obviously he aint making many expensive parts. if you got $20,000 part with a oversize bore it can be a very expensive rework job
    I worked in an automotive machine shop, so a lot of the work was ‘boring’. Usually the head machinist would handle that task, however in order to aid in my learning I was encouraged to measure and check bores.

    Often enough we used telescoping gages. An indicating bore gage doesn’t fit inside of something like a differential housing. For bores that had easy access of course we used an indicating bore gage because as you note, it’s easier and offers the ability to check for ovalocity.

    I don’t recall ever using an inside mic, I don’t recall if that was the machinist’s preference or if there were further logic to it.

    We did use calipers, mainly just for ‘ball-parking’, never for precise work.

    Anywho, I mention this simply to ask what you typically measure with when the part is on the machine? I don’t always, in fact rarely have access enough to a bore to check it with an indicating bore gage, but often enough I do have room for snap gages.

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    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.

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    I'll also just add:

    A VERY MERRY CHRISTMAS TO ONE AND ALL.

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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.
    I’m not sure if this directed at my comment. We used high quality calipers, not some second hand stuff. Currently, I use mine a lot so I‘ve performed all of the certification procedures on my own calipers. I know they’re accurate to .001” in almost all circumstances according to gage blocks.

    However most of the boring jobs were to house a bearing or to retain a sleeve and so a higher degree of precision provided a measure of confidence.

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    Reaching in, up & around things, often done in-situation with beam type calipers is for most a non starter. My ID mics only go down to 1-1/2 inch so telescoping gages or ID spring calipers are the weapon of choice for me. Same with getting my longer dial bore gages around in confined spaces.

    It’s life in the real world. Id often set my portable bore welding torch tube with spring calipers. When the (digital) voltage display stayed steady I knew the torch center was inside of .010”ish. Not bad for setting things at arms reach without any real scale.

    Good luck,
    Matt

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    Quote Originally Posted by BHolcombe View Post
    I’m not sure if this directed at my comment. We used high quality calipers, not some second hand stuff. Currently, I use mine a lot so I‘ve performed all of the certification procedures on my own calipers. I know they’re accurate to .001” in almost all circumstances according to gage blocks.

    However most of the boring jobs were to house a bearing or to retain a sleeve and so a higher degree of precision provided a measure of confidence.
    My post wasn't directed at you. Just general. As you say, to house a bearing requires more accuracy than a caliper is capable of.

    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.

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