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Those numbers on a fishtail gauge

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  • #16
    Center Gage heaven

    I use em too because you don't need any books, you just read it off the little fishtail gage for the thread pitch you are making, and that is the depth of the bottom of the thread. Since I'm a baby, I run a flat at both ends of the thread that is the depth of the bottom.
    I am looking for the impossible... a center gage with finer threads double-depth numbers on it. Exists???

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    • #17
      Originally posted by John Stevenson
      It's because the Chinese just copy everything without query
      ...
      You got a set of those #@*^'ed up 1-2-3 blocks too?

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      • #18
        This thread was interesting 3 1/2 years ago when Marv first brought it up!! Should hold some interest for new members as well.
        - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

        It is true, there is nothing free about freedom, don't be so quick to give it away.

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        • #19
          Les as an apprentice I was taught that those are arbors, not mandrels. Arbors hold tools, mandrels hold work.
          This was a mandatory question, miss it , fail the test.

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          • #20
            It is an interesting old thread and is answered rather well here:

            http://www.schsm.org/html/fishtail_gauge.html

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            • #21
              All the angles

              I never use a "fish-tail" or threading guage.

              https://www.machineryhouse.com.au/Pr...stockCode=Q612

              Getting the angle set on a small section of the tool is a "big ask" as is getting the "fish" parallel to the job or the tail-stock quill as regards accuracy.

              I use vernier or digital protractors and/or bevel guages to grind the tool angles as well as setting the tool edge to the face of my lathe chuck or face-plate etc. as well as the top-slide angular off-set (1/2 tool angle less 1/2>1 degree etc.) as it is very quick and accurate:







              Depth of thread and root diameters are available on readily accessible tables everywhere.

              http://i200.photobucket.com/albums/a...read_form1.jpg

              http://i200.photobucket.com/albums/a...read_form2.jpg

              http://i200.photobucket.com/albums/a...read_form3.jpg

              http://i200.photobucket.com/albums/a...read_form4.jpg

              http://i200.photobucket.com/albums/a...read_form5.jpg

              http://i200.photobucket.com/albums/a...read_form6.jpg

              http://i200.photobucket.com/albums/a...read_form7.jpg

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              • #22
                The numbers on the center gage are the depth of the run out grove & chanfer if your going to cut a chanfer on the leading edge. Or at least that is what I have been taught. If you were cutting 1" stock w/12TPI you would infeed 1/2 the double depth or .054 and would wind up with .108 double depth. 1" - .108=.892" thats what your mic should read & that would be your run out grove. I was also taught to add .005 to the infeed on the run out grove, when you start to scratch cut in the run out you are at your thread depth.

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