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Why 68 Deg. for inspection

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  • 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.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  • #2
    I'm gonna guess that 20C, as a nice round number, entered into the thinking.
    Lynn (Huntsville, AL)

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    • #3
      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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      • #4
        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

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

          Ed
          For just a little more, you can do it yourself!

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          • #6
            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
            .

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            • #7
              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, 11:37 AM. Reason: historical accuracy

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              • #8
                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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                • #9
                  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?

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                  • #10
                    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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                    • #11
                      Aviation settled on 15c and 29.92 inches as the "standard day".

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                      • #12
                        Originally posted by epicfail48 View Post
                        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
                        Yes BUT With all the hullaboo over the GREAT METRIC system they seem to have something wrong with the factor TEN .
                        Tne bloody idiots seem to have forgotten DECI and DECA in their prefixes. SO! if youre so all hipped up on this factors of ten you had better start using the "forgotten" to of them. BAH!
                        ...lew...

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                        • #13
                          Originally posted by RB211 View Post
                          Aviation settled on 15c and 29.92 inches as the "standard day".
                          That 29.92 comes from the standard atmospheric pressure, with a 10 ft adjustment made to represent an approximated height of the altimeter sensor's mounting location in the plane above the runway. Ten feet was reasonable back when the altimeter standard was established, now not so much.

                          Don't know about the temperature. Maybe it was the temperature used as the mean in converting station pressure to sea level. ...in fact, that kinda makes sense.
                          Lynn (Huntsville, AL)

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                          • #14
                            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?
                            Your use of 'Mericans instead of Americans I find highly derogatory.
                            You find it weird and have a problem with the name Daniel Gabriel Fahrenheit.
                            You apparently are accepting of the name Anders Celsius, possibly because he
                            uses ten based numbers for freezing and boiling.
                            Are your rationale's based on emotion or selfish needs for fulfillment?

                            -Doozer
                            DZER

                            Comment


                            • #15
                              Originally posted by epicfail48 View Post
                              ...

                              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
                              Sounds to me that you are too lazy to remember things like one miles is 5280 feet.
                              Are you afraid your brain will leak out your ear????

                              -Doozer
                              DZER

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