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Those numbers on a fishtail gauge

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  • woodey
    replied
    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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  • oldtiffie
    replied
    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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  • dp
    replied
    It is an interesting old thread and is answered rather well here:

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

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  • tdmidget
    replied
    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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  • Your Old Dog
    replied
    This thread was interesting 3 1/2 years ago when Marv first brought it up!! Should hold some interest for new members as well.

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  • websterz
    replied
    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?

    Leave a comment:


  • Mosey
    replied
    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???

    Leave a comment:


  • LES A W HARRIS
    replied
    Thread Tool Setting Gauges

    Can not recall the numbering, (use it or lose it), worked things out ahead of time, However I used a different type origanaly, as we learned Whitworth, BA, & Unified.



    But did use the fishtail on taper threads, The apprentice school made lots of basic stuff for the main works, taper threaded mandrels for buffing machines, being the taper thread exercise.



    Cheers,

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  • John Stevenson
    replied
    Forrest,
    Believe it or not that's yet another book I have to buy <sigh>

    I am a bit wary though about peoples views of Whitworth though given the age in which he lived. In those day to get anywhere with Government backing and support you had to be sponsered, a bit like your lobbiest.
    Just who you had as a sponsor and just who the opposion had meant a great deal.
    Whitworth was a hands on dragged up by his boots guy who felt that sucess and results meant more.

    Others had already worked out that political clout mean more.

    This led to the fiasco over the Armstrong guns verus the Whitworths when results spoke volumes but they addopted the very inferior Armstong pattern due to political pressure.

    As regards the threads I do remember reading a wartime standard where it stated that the original Whitworth thread FORM was still something like 23% stronger that any of the current thread forms.

    Many forms were modified from initial introduction but the Whitworth has stayed as it was first designed.

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  • Forrest Addy
    replied
    Sir John. Read what Charles Porter had to say about Mr Whitworth's organization in the 1860's in his "Engineering Reminiscences" Chapter 11 thru 13. It's an interesting contemporary account of the later years of one of the giants of the Industrial Revolution written by someone knowledgeable if a bit biased.

    I wonder what Bill Gates' peers will have to say in years to come.

    Leave a comment:


  • wierdscience
    replied
    Maybe I'm a real machinist after all

    -Since I know that the table on the gauge is used for determining the the size of tap drills for American or US standard threads.

    It gives in thousandths the double depth of tap and screw in the pitches most commonly used.

    Also works in calculating the minor diameter of a hole to be single pointed in the lathe,it's what you do when you need the minor for a 6-5/8"-24 thread

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  • lane
    replied
    I use the Double depth to subtract from the max dia. for thread relif groves

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  • japcas
    replied
    I use the numbers on the center finder quite frequently. When I'm running a cnc lathe and programming the part where a thread is at, I can simply look at the center finder, find the double depth of thread that I am programming for, divide it by 2 and then I'll add .010 to .020 to it for the chamfer at the start of the thread. Maybe not the best or only use for it, but it's a quick reference.

    Leave a comment:


  • IOWOLF
    Guest replied
    Because you can put it between work and thread tool to see if you are on center,like a 6" scale.

    Getting my flame retardant clothes on now.
    Last edited by ; 05-19-2006, 02:26 PM.

    Leave a comment:


  • John Foster
    replied
    Why center gages?

    Jim, because they can be used to check the 60آ° point on a lathe center. John

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