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  • Threading Help

    Hi,

    I’m planning to cut some threads and I’ve managed to confuse myself. Perhaps someone here can help straighten me out. Or coil me up, as the case may be.

    To start: I’ve got some laydown threading toolholders and indexable inserts

    The external inserts are 16ER AG60. The internal ones are 16IR A60. I suspect this is critical info as the profile of the tool should affect the depth of cut, right? If it's a sharp vee you'd cut deeper than if it's a rounded profile...

    I’d like to cut 1"-40 external threads on a shaft, and 1”-40 internal threads on a collar that will be threaded onto the shaft.

    I’m having a very difficult time figuring out:
    (a) What should the starting OD/ID values be for these two parts?
    (b) What should the depth of cut be for the finished threads?

    Without going into all the things I’ve done to tie myself in knots trying to figure this out, can anyone either point me in the direction of the calculations I should be using (teach me to fish) or suggest the correct values (throw a fish my way)?

    Would be much indebted for any assistance.

    Thanks!
    -Ben

  • #2
    Welcome, very interesting first post.

    I think the place I would start would be finding out more information about the inserts. An online catalog from the manufacturer should give you all kinds of information about things like profiles, depths of cut etc. as well, I suspect, things like speeds and feeds.

    The thread you are contemplating cutting is very specific and while it certainly may be an existing thread to me it is not "common" (it could be, just for something I have even less of a clue about). I do not have the knowledge to suggest a different thread but I would say that if it is a "one off" as long as the internal and external threads fit well to one another, at some level (of discussion if nothing else) that is what they need to do, fit well to one another, this in turn means you can have values that work to arrive at the final fit you want but may not apply to any other thread, of that or any other size (there will be, no doubt some discussion about classes of thread fit when those more knowledgeable than I respond).

    I am often more of a "teach to fish" person (it is my style of coaching sports), so again where I would likely start would be with a reference like "Machinery's Handbook" for (a) the general discussion about threads, thread forms and thread systems, (b) for the discussion of variations between types of threads more closely related to the questions you are asking (ID/OD and depth of cut), (c) formulas that relate pitch diameters, depths of cut etc. so, if nothing else, you have some information to begin or consider before beginning.

    By the by, if I have found correctly, that 40 tpi is a #6 fine screw so on an inch diameter shaft, is very, very, very fine. Fine threads can certainly be found on larger diameters but in most cases, as far as I know, they are not very long (along the axis I mean)
    Last edited by RussZHC; 05-21-2015, 06:20 PM.

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    • #3
      1" - 40 TPI
      External diameter 1" max. [depth of cut = .61343/tpi = .0153" (minimum.)]
      Internal minor diameter = 1" - 2(.54127/tpi) = .9729"
      Internal depth of cut = .54127/tpi = .01353" (minimum).

      More data here http://un-unr-unj-threads.tripod.com/#C2
      Last edited by basalt; 05-21-2015, 09:56 PM.

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      • #4
        If I were cutting those threads I'd go hit KBC Tool for both the proper INTERNAL and EXTERNAL full profile inserts for the 40 pitch thread. The have flat rate $8.95 shipping right now.

        With that you do the external thread first, making the blank to the nominal ط1" diameter or a few thousands over. Cut thread until the full form insert cuts the tops of the thread, bringing the major O.D. of the thread to ط0.997". Now you have a beautiful burr free thread to use a the gauge for the internal thread.

        Bore to ط0.965" and thread until the threading insert crests the internal thread, proceed slowly until the gauge fits in smoothly.

        Done, and perfect threads every time.

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        • #5
          Interesting, PixMan.

          That may be the best answer. I'm not sure I really want to commit $50 to inserts for cutting one set of threads, but I like the simplicity. Hmmmmmm....

          Comment


          • #6
            For one set of threads, you could grind a couple of HSS tools for about $3.00
            The page that basalt posted looks like it has the critical dimensions you'll need for the cutter.

            Tom Griffin has some excellent videos on threading tool geometry and grinding.

            https://www.youtube.com/watch?v=VK8JfhD_FxY

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