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  • Old School Accuracy?

    Recently I was given a 1923 edition of Tool and Gage Work. Since DTI's and accuracy has been posted about more than a bit lately. I thought some here might be interested in what those old school guys were able to accomplish with what would be considered today as very simple tooling that was built in the same shops it was going to be used in. It seems that tool makers back then were expected to build their own DTI's.

    They show a manual test indicator that according to the book, Multiplies the tip movement 170 times and then transfered that movement to a simple scale that looks to have about .100-.200 between the divisions.

    Using that DTI, And hardened, ground, and lapped tool maker buttons. The book then goes on to explain how master jig plates were built for the watch making industry. The day to day factory jig plates were then copied from this master plate. They were using a lathe and faceplate to bore and then very lightly ream the holes in this master plate. Alignments using that DTI against the toolmaker buttons were expected to show no or very little movement on the indicator needle. The book then states a needle movement of .004 that should be able to be seen by eye, Would give you readings that showed the tool maker button to be out of true position by .000012. And this was all done by tapping the plate into final position by hand on that lathes faceplate. No doubt all of this was done on a plain bearing lathe and a ground and lapped faceplate.

    The book also shows a drawing for building a DTI.

    Pete

  • #2
    Here is the "3-button" principle:

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    • #3
      its unbelievable, because anything below 0.001 mm in acuracy is unmeasurable in my opinion by mechanical methods. just consider the influence of temperature or mecanical flex.

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      • #4
        Dian,
        I'd pretty well have to believe what's written in this book since it was written for and about the tool and gage industry. I've read a fair amount about some more than impressive accuracy specifications done a lot longer ago than anyone generaly thinks was possible. Later on in this book they go into pretty good detail about the then brand new Johannson gage blocks that were accurate to within millionths. But yeah, You are right about the temperature problems.

        Pete

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        • #5
          Originally posted by dian
          its unbelievable, because anything below 0.001 mm in acuracy is unmeasurable in my opinion by mechanical methods. just consider the influence of temperature or mecanical flex.
          If you are not using a climate controlled metrology room you're correct. That said, it would be interesting to measure some old tooling with modern electronic measuring devices to find out just how accurate they were.

          BTW, I have a set of JoHansen blocks (the real deal with the Ford emblem) with an accuracy chart that gives the variation for each block in millionths of an inch.

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          • #6
            I absolutely love learning about the old school techniques like this. Our predecessors deserve a lot more credit than we often afford to them. I recently studied the work of the late 18th/early 19th century watchmaker Abraham-Louis Breguet, and was completely awestruck by what he was able to accomplish with the technology available at the time.

            This reminds me of another old-timey trick using a similar principle of mechanically amplifying inaccuracies. I know of it as a "wobble stick", perhaps it has other names outside of the instrument-making crowd. This fellow gives a brief summary on one he made for his own use: http://watchmaking.weebly.com/wobble-stick.html

            Being a complete amateur, with a small shop in my basement, on a shoestring budget, I tend to hoard information on traditional low-tech operations like this, as well as investing in making as much of my own tooling as possible.

            I don't suppose anyone else here has any old timey techniques they care to share?
            Max
            http://joyofprecision.com/

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            • #7
              Originally posted by dian
              its unbelievable, because anything below 0.001 mm in acuracy is unmeasurable in my opinion by mechanical methods. just consider the influence of temperature or mecanical flex.
              Originally posted by uncle pete
              Dian,
              I'd pretty well have to believe what's written in this book since it was written for and about the tool and gage industry. I've read a fair amount about some more than impressive accuracy specifications done a lot longer ago than anyone generaly thinks was possible. Later on in this book they go into pretty good detail about the then brand new Johannson gage blocks that were accurate to within millionths. But yeah, You are right about the temperature problems.

              Pete
              1 micro-meter (micron = um) is near enough to 40 micro-inches.

              0.001mm ~ 0.00004" (almost "half a tenth") which is quite measurable - with care - with good tools in a good HSM shop

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              • #8
                Originally posted by Dr Stan
                If you are not using a climate controlled metrology room you're correct. That said, it would be interesting to measure some old tooling with modern electronic measuring devices to find out just how accurate they were.

                BTW, I have a set of JoHansen blocks (the real deal with the Ford emblem) with an accuracy chart that gives the variation for each block in millionths of an inch.
                Dr Stan,
                Your original Ford marked gage blocks would be more than a very rare item today. I wouldn't think there would be too many of those sets left. There's got to be a good story behind finding something like that.

                Pete

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                • #9
                  Originally posted by uncle pete
                  Dr Stan,
                  Your original Ford marked gage blocks would be more than a very rare item today. I wouldn't think there would be too many of those sets left. There's got to be a good story behind finding something like that.

                  Pete
                  I picked them up from a shop that was closing in Florida. Have no idea where they were before that.

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                  • #10
                    Time to contribute to a living ledgend...

                    For any of you who have been to the Wyandotte show in Michigan you are likely familiar with the Corliss (spelling?) steam engines and scale Hardinge lathes of Bill Huxhold (the beauty of which came close to bringing tears to my eyes).

                    At any rate when he was getting near to retirement he was building prostheses for amputees. I was shocked to learn the accuracy required for those joints...down into the tenths of an inch. So when he was getting ready to retire they started trying to make the parts he did with his basic machine tool (admittedly top quality) using CNC and were unable to achieve the level of accuracy that he did. (This was, I suspect, back in the 80's).

                    Bill is getting along in age and I'm not sure if He'll be in Wyandotte this year but if you like to be boggled by quality you deserve to have a look at his work. Some day I hope to qualify as a "piker" compared to his work.
                    Allans Rule: Anything worth doing is going to be a pain in the butt.

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                    • #11
                      Clevelander,
                      Those are for sure some more very good examples of just what some people are really capable of. I very much think we have a few on this forum who are just as good also. Some machinists and even some so called hobbiests really are masters of their trade.

                      Just HOW they do what they do would be very interesting, At least to me anyway.

                      Pete

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                      • #12
                        Agreed Pete, some very impressive work shows up on this site!!

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                        • #13
                          Dr Stan brought up a very interesting idea about checking some of this old tooling against modern metrology equipment. I recieved something in the mail today that was built in 1952 and measured to 5 decimal places. Now I just need to find a place that can 100% verify their measurements for accuracy in B.C. I just don't know quite enough about all this to know where to search for a company that can do this, And is somewhat local. Mailing this away for testing is not worth the risk.

                          Pete

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                          • #15
                            Oldtiffie,
                            My Mitutoyo gage blocks would do most of it. But probably just for my own interest this might take a company or university with a very high end CMM. There's some historical details behind this so I won't take a chance mailing it.
                            Your one link may provide some business names within B.C. Thanks.

                            Pete

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