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  • Something to ponder

    I'll be honest, I was just thinking about this in the shower and havent researched it yet, but you ever wonder how accurate the inch measurement is on our older tools? My astronomy teacher was telling me that he was at a conference when they nudged the size of the Inch to = exactly 2.54 centimeters. He is not that old of a guy, so my 1941 southbend is obviously from before they changed the size of the inch. Was the change so insignificant that it has no bearing in machine work?

  • #2
    Sorry Bill, but he's full of it. The inch has been defined as 25.4mm for a long time, mid 19th century IIRC, except for survey work for some obscure reason, so we acctualy have two inch deffinitions in this country.

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    • #3
      As I understand it and I could be wrong the only federaly recongnized system of measurement is the metric system as per act of Congress. And I thought the ratio between inchand metric was set then (curiously the meter which is supposed to be 1 millionth of the distance from the pole to the equator was figured wrong to start with IIRC). Actually the history of uncertified instruments goes back to the Egyptians. It seems temple priests had measuring devices that were intentionaly short by 10% so as to convince the peasants that they had bigger fields than they did and squeeze more tax outof them
      Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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      • #4
        I thought the metre was defined as a multiple of the wavelength of some atom?

        I also thought that the inch was undefined as it was derived from approximation which became a standard? Kinda like a cubit was an arms length, which by definition is the length of ones arm and is not the same for anyone - inch was the same deal and as the world became more industrial it was set as a standard..... But I could have imagined the whole thing...

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        • #5
          Survey inch and foot are still used for survey work. That is the original standard for the meter but it dates from the eighteenth century and has been revised several times. I belive it now uses wavelength of light.

          BillH your proffesor was probibly refering to the 1958 conference for defining the international inch. Basicly the UK, Canada, and the U.S. which created a common standard among them, but the inch was defined in metric terms long before that.

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          • #6
            An inch is defined as one twelfth of a foot, and is from old english and literally means 'a twelfth'. So far I have only been able to see a fott defined as 12 inches.... go figure....

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            • #7
              http://www.sciam.com/askexpert_quest...D=3&topicID=11

              John

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              • #8
                my late father was a cabinetmaker,and he always referred to the size of nails in"thumbs".this was in holland,which is otherwise metric.is the "inch" perhaps related to the "thumb"?Also perhaps US "penny"?In the rag trade(clothing),an old measure was an "ell".this was the arm length that ben referred to.i believe this was about a yard.As for weight,a half kilogram was a pound,and a tenth kg an ounce,but these were thrown out in the mid 60's.This mixing of measurements apparently came about in the "golden century",(the 16th),when dutch ships were trading all over the world.hans
                p.s.something unusually large was sometimes referred to as a "bonker"!this word has a slightly different connotation today!
                Hans

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                • #9
                  Prior to the redefinition of the inch in '58, 59 or '63 depending on what country you are in the inch was equal to 25.39997mm. Since then it was redefined to be 25.4mm. Not enough difference to notice Bill.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    This is how it works:
                    First you pick an arbitrary unit, similar to a gesture made during conversation and beer after a fishing trip.
                    Then you make the same gesture to a retentive scientist from France and let him decide how many wavelengths of light it comes to and relate it to a whole nuther set of arbitrary units. Then they call it a system.
                    That's the way it's always been.

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                    • #11
                      I'm sure that you will be able to file to fit whatever it is you are making

                      Allan

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                      • #12
                        Bill, in the shower??
                        I have always understood an inch to be 25.4mm.
                        Confusion only happens when measuring length from either above or below. I have heard that it`s how its used that is more important
                        Ken

                        [This message has been edited by speedy (edited 11-25-2004).]
                        Ken.

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                        • #13
                          speedy, you beat me to it, checking an inch in the shower. Gets you to thinkin don't it
                          sounds like a dirty old man to me
                          Jim

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                          • #14
                            I hope it was a cold shower if a inch and your tool came to mind. Just kiddin lol

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                            • #15
                              Since I tattooed a ruler on my left index finger I now shower in the dark.

                              David not really..

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