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Thread: Why 68 Deg. for inspection

  1. #1
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    Default Why 68 Deg. for inspection

    Why was 68F (20C) chosen as the temp for measuring parts for inspection. I understand why you want a constant temp but why 68 and not 70 or 72???
    The shortest distance between two points is a circle of infinite diameter.

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  2. #2
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    I'm gonna guess that 20C, as a nice round number, entered into the thinking.

  3. #3
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    It has to be some temperature or other. That particular one is a comfortable working temperature, not too extreme for heating or air conditioning to work economically.
    I may be wrong, but I thought the Tesa ring gauge that I have says Standard at 25C. I will have a look at it on Wednesday.

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    In QC at work, the new quality guy raised the temp in the lab thermostat
    from 68 to 69 one day, and the old quality guy had a thermonuclear meltdown!
    He proceeded to rip the thermostat off the wall.
    Me being Doozer, I said, "Well now that the A/C is broke, it is gunna get a whole
    lot hotter in here than 69"!!!
    All that drama, and I was NOT in the middle of it this time.

    --Doozer
    DZER

  5. #5
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    So called "room temperature" has historically often been defined as 20 degC. That converts to 68 degF.

    Ed
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    Quote Originally Posted by ed_h View Post
    So called "room temperature" has historically often been defined as 20 degC. That converts to 68 degF.
    good luck getting that one to fly with the ladies in the office
    .

  7. #7
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    It goes back to when Johanssen created his gage blocks. The common average temp in European QC labs at the time was 68F or 20C. When Johanssen lapped his first block, he sent it to the Bureau of Weights and Measures in Sevres and asked them to determine the temperature when it was at a nominal length. He then used the coefficient of expansion to hit his exact number, and create the rest of the blocks in the set.
    Last edited by nickel-city-fab; 07-09-2019 at 10:37 AM. Reason: historical accuracy

  8. #8
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    For what it may be worth, 68* is also the correct temperature for developing camera film. Variations above or below that target require longer or shorter developing times.

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    Quote Originally Posted by nickel-city-fab View Post
    It goes back to when Johanssen created his gage blocks. The common average temp in European QC labs at the time was 68F or 20C. When Johanssen lapped his first block, he sent it to the Bureau of Weights and Measures in Sevres and asked them to determine the length of it when it was at 20C. He then used the coefficient of expansion to hit his exact number, and create the rest of the blocks in the set.
    Thankyou.
    Again, the 'Mercans are the odd ones out.
    Most of the Rest of the World is Centigrade.
    Most people in the world would just look at you weird when you say 68 Fahrenheit.
    Fahenwhat?

  10. #10
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    Quote Originally Posted by thaiguzzi View Post
    Thankyou.
    Again, the 'Mercans are the odd ones out.
    Most of the Rest of the World is Centigrade.
    Most people in the world would just look at you weird when you say 68 Fahrenheit.
    Fahenwhat?
    Much as I hate the imperial system, Fahrenheit actually makes a bit of sense. It more accurately encompasses the range of temperatures that humans live in, inside that 0-100f range, and rounds easier. Saying "its in the 70's" covers a narrower range than "its in the 10's c".

    That's said, imperial measurements deserve to die a painful death. 100 centimeters to the meter, 1000 meters to the kilometer makes more sense than 12 inches to the for, 3 feet to a yard 5612 or some such nonsense feet to the mile, its a mess

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