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  1. #21
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    Those of you who like the three point hole mics haven't priced the 250mm versions.

    As for setting bore gages, look up Sunnen's setting fixture. Highly accurate and easy to train capable but inexperienced people to set bore gages.

    A three point hole mic will be faster to measure a hole if the proper piece is setting on the shelf. Most only have .0002" resolution, so not as good of resolution as a bore gage. Since a 3 point gage is an averaging gage, it is more difficult to detect and quantify out of round or taper than a bore gage.

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    Bore mics are ok, but i wouldnt use them on a +/- .00035 tolerance unless it was for a second reading. Make a plug gage. Another thing as stated above, you may want to make sure your round...roncon

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    AIR GAGE, checks roundness and size at the same time. make up all the plugs and masters one time, and keep them in a library. Also for the larger pieces, a lazy susan arraignment to lay the part on and slowly spin the part. My 2 cents.

    Chris

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    gbent has some good arguments!

    If you do have a dedicated setting fixture, things get easier. Don't know the Sunnen's one.


    Nick

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    While go/no-go gauges can be cost effective compared with three-point hole mics in larger sizes, there's an important piece of information missing:

    How many different sizes are you dealing with?

    You made the comment "around 250 mm - only a few parts this size, and all within a fairly close range"
    The selection of an appropriate methodology at this size is critically dependent on the number of different sizes.

    Each size requires a different go/no-go gauge, while a single three-point mic can handle a range of sizes with equal accuracy.

    - Leigh

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    Quote Originally Posted by Nick Mueller View Post
    gbent has some good arguments!

    If you do have a dedicated setting fixture, things get easier. Don't know the Sunnen's one.


    Nick

    The Sunnen setting fixture is a breeze to use. If you've never used one, you are in for a treat when you do, it takes all the fiddling out of using a bore gage. The thimble is about 1.5" in diameter, and has a big magnifier above it to aid in reading it. The bore gage sits on a stage so you don't have to hold it in place while setting it. You screw the appropriate sized extension into the gage, set it in the setting fixture, turn the extension to the right length to get the dial gage hand near your desired location to zero it, lock the locknut, then finish the calibration by turning the dial to put zero where the indicator hand points. Rock the gage a bit just to be sure it repeats and you are done. The fixture comes with a ring gage to verify it's calibration, I've used gage blocks also directly in the fixture.

    There's one fixture for 2" and up, another for under 2" gages.

    I have a question for the people who are recommending tri-mikes over bore gages - Have you used a Sunnen bore gage with all the related equipment? I have both, and I greatly prefer the bore gage unless I'm looking for tri lobed bores. The tri-mikes are probably better for a dirty production environment where they are in skilled hands and might get showered with chips and dirt, but that doesn't sound like what the OP needs. I also find that the Sunnen bore gage allows me to quickly find the highest and lowest points in an out of round hole.

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    Hi all,

    Thanks very much for all your input. It's looking like a tie between hole mics and dial bore gages, so I'll investigate each more closely and see what I can find. I'm leaning towards bore gages purely from a cost perspective, although I realize I'm going to be spending a whole mess of money regardless...

    Also, just to clarify: We're a small company, and our lot sizes (since we do JIT purchasing) are commensurate - we can't ask our suppliers to all perform first-article inspections/etch lot numbers onto parts/etc. at our volumes (even though we'd love to be able to do so). Our suppliers are typically pretty good, but a) we're always looking to diversify our base, and consequently have to take chances on new folks, and b) sometimes mistakes happen. At that point, it's a matter of determining whether Part A or Part B is out of tolerance, and then sending it back to our suppliers (who do the rework for free).

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    With that tolerance go/no-go plug gauges may not give you an accurate check of the actual size of the hole. If it is out of round you will get a false positive or negative. The bigger the hole is to inspect the more of a chance you can get to have the hole out of round. Larger plug gauges are also more difficult to get straight in a hole to get an accurate inspection also. In my experience the air bore gauge is the most accurate gauge for the job.

    I once had an inspection company tell me that their cmm was the most accurate gauge ever. I believe they were only fooling their self. I never did get along with inspectors anyway so maybe I was always wrong.

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    Gorden/Nick - thanks for your input. Yes, price is very important to us since our business is very competitive. Since we have a very large and complete stock of inch and Metric round plug, flat plug, thread-, snap-and many other types (air-,three point-, Sheffield gages, CMM's etc.) available to us - going back to doing some of our own inspection was the best solution for us. Even with "just in time" you always could end up with some good parts to buy you some time. We also kept all the tooling and gaging for our outsourced parts and therefor we are able to overcome some of the difficulties one experiences with outsourcing. So this works OK for us. One problem is creeping up on us. We outsourced some highly precision and complicated parts.
    We kept all tooling and gaging. Now after years using a good and reliable vendor (overseas), we are being told that because of smaller and smaller lot sizes they would not be able to supply us. Bringing the part - a very complicated crankshaft - back "in house" would be very difficult since the people familiar with the manufacturing of this part are no longer available (retired). We are now working with one company. Hope it works out.
    I guess it is always easy to find a vendor for as long as you require large numbers, but when those numbers go down - watch out!

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    True 534- but out of round can be a problem with all measuring devices, especially when you don't have the qualified people available to you and you can not afford to buy expensive equipment..
    For the large dia. like 250mm a ground "Go-NoGo" plug would most likely act more like a functional gage.

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    There is a lesson to be learned here. Those of you sometimes working in the metric system - you may have heard someone referring to the two systems of "Fits and Tolerances" namely "Standard Bore (Hole)" and "Standard Shaft (Arbor).
    After reading thru this thread and seeing how expensive it can be to just buy the needed gages to measure just a few holes you will
    understand why most manufacturers opt for using the system of "Standard Bore". That means one thing: The tolerance for a hole will have a Position "H" tolerance and the shaft is made to different tolerances positions like a "m" or a "p" to achieve the desired fit. It is much cheaper (and easier) to measure the outer dia. of a shaft. A simple Micrometer covers a big range and a set of three or four does not cost you an arm and a leg. There are also many other ways to check an outer dia.. It also cuts down on the cost for tooling (reamers etc).
    There are reasons why some manufacturers decide to go with a "Standard Shaft" where the shaft has a Tolerance Position of "H".
    In that case they alter the hole to achieve the desired fit (sliding, loose or press fit). Could be that they have a ready supply of standard shaft material or they find it easier to produce a hole to achieve a certain fit.
    In general it must be said that most manufacturers prefer to work to "Standard Hole".
    Anybody changing or going into Metric should think about this since making the wrong decision could be expensive. Making the right choice could result in big savings.

  13. #32
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    From what I read, I believe you are checking bushings. Quick question, are you checking them after they are installed? Possibly they are crushing after the install and giving a bum reading.

    Regardless, when it comes to tools you get what you pay for. If you want an easier way to check parts that is less likely to be miffed up, buy the air gage setup.

    If you want to train some people and spend less on hardware, buy a cheaper tool.

    Just my two cents.

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    Quote Originally Posted by juergenwt View Post
    There is a lesson to be learned here. Those of you sometimes working in the metric system - you may have heard someone referring to the two systems of "Fits and Tolerances" namely "Standard Bore (Hole)" and "Standard Shaft (Arbor).
    After reading thru this thread and seeing how expensive it can be to just buy the needed gages to measure just a few holes you will
    understand why most manufacturers opt for using the system of "Standard Bore". That means one thing: The tolerance for a hole will have a Position "H" tolerance and the shaft is made to different tolerances positions like a "m" or a "p" to achieve the desired fit. It is much cheaper (and easier) to measure the outer dia. of a shaft. A simple Micrometer covers a big range and a set of three or four does not cost you an arm and a leg. There are also many other ways to check an outer dia.. It also cuts down on the cost for tooling (reamers etc).
    There are reasons why some manufacturers decide to go with a "Standard Shaft" where the shaft has a Tolerance Position of "H".
    In that case they alter the hole to achieve the desired fit (sliding, loose or press fit). Could be that they have a ready supply of standard shaft material or they find it easier to produce a hole to achieve a certain fit.
    In general it must be said that most manufacturers prefer to work to "Standard Hole".
    Anybody changing or going into Metric should think about this since making the wrong decision could be expensive. Making the right choice could result in big savings.
    This could maybe illustrate the point. It's even an American ANSI standard.

    http://mdmetric.com/Ch6.8wGO.pdf

    Page 11 gives a pretty good idea of how large H/h is for various diameters and tolerances.

    Already mentioned but worth repeating. A capital letter (e.g. H) is always internal and a small letter (e.g. h) external.

    For example 25H something is always nominal and then + something and 25h is always nominal and then - something.

    e.g. from page 11

    100H8 is max 100.054 and min 100.000
    100h8 is min 99.046 and max 100.000

    Gordon

    N.B. the system is in principle the same for metric threads but pitch diameter tolerances are much larger than non thread tolerance plus the letter and number are "reversed" e.g. M36-6H / M36-6h.

    http://www.boltscience.com/pages/screw8.htm

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    Hello dear, I have read your suggestions , they were really great. But I have a question , What is your prefer for measuring large holes like 250H7 or 400H7 ? as far as I know using bore guage for this sizes is not so consistent, and because of quantity of the job we can not produce Go/No Go gauge , so I have decided to use T- Gauge or telescopic gauge, but unfortunately I couldn't find T-Gauge larger than 150 mm ...
    so I need your experince ,,,
    thanks a lot


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