Large Diameter Pi Tapes
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  1. #1
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    Default Large Diameter Pi Tapes

    I am wondering if anyone knows where I can find a Pi tape that can measure a 18' diameter and also 16'-3" diameter. Any help is appreciated.

    Thanks

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    Bah, just use a piece of banding strap and a little math. If you're producing the same diameters, then you can put a mark at nominal and two marks on either side of your tolerance for fast, mistake free QA.

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    A measuring tape and any el cheapo $2 calculator.

    - Leigh

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    Why, from Pitape.com!

    http://www.pitape.com/products-extendedrange.htm

    It looks like the .001 stop at 12' diameter. For 12'-18' they only read to .010.

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    Default Pi tapes and large diameters

    "For 12'-18' they only read to .010"

    thats because a pi tape that big stretches and is also hard to hold it square. if held at a slight angle it will read a larger diameter than it is actually.

    pi tapes are rated to dimension with a certain pull or tension at a rated temperature (usually 20 degrees Celsius)

    When doing large scale straight measurement with metal tapes you often need 4 people.
    1) to hold one end
    1) to pull with a spring scale
    1) to use magnifying glass on zero end of tape measure
    1) to use magnifying glass (or headband magnifier or microscope/telescope) to read tape measure
    verbal communication that zero end is "good", spring scale is "good" then reading is recorded. also the tape measure support that is continuous or 2 or 3 or 4 point support will give different readings. We use a calibrated tape measure that came with a 100 page computer printout showing how tape measure will change reading depending how it is supported.

    Large scale measurement repeatability is not as easy as it appears.

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    Pi tapes are pretty much self-centering if you slip it sideways each direction a few times while holdng teension. I used to tape it to the work at several points around the circumference for support with bandaids so the tape was free to move under the gauze part.

    I have a whole set of pi tapes from 2 ft to 12 ft somewhere in my stuff.


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