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diameter of rod for hand thread

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  • #16
    "Mind your manners" when undersizing..... the die may take a notion to cut deeper on one side than the other, and give you an off-center thread, if you get just a little too far under.

    There is a practical "end" to it also.... if you can, cut a sacrificial extra length even more undersized, to the minor diameter. That will keep the die straight when starting. The average die holder is a bear to keep straight when threading by hand. A few have devices to hold them straight, but inevitably there will be some feature of the part (being too short, perhaps) that make those impossible to use.
    CNC machines only go through the motions.

    Ideas expressed may be mine, or from anyone else in the universe.
    Not responsible for clerical errors. Or those made by lay people either.
    Number formats and units may be chosen at random depending on what day it is.
    I reserve the right to use a number system with any integer base without prior notice.
    Generalizations are understood to be "often" true, but not true in every case.

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    • #17
      Don't know how it would work with imperial threads, but with metric you can usually shoot for a diameter that is 1/10th of the pitch smaller than the nominal. So for example M42 x 3 would nominally be 42 mm OD, but I would make it 1/10 x 3 = 0.3 mm smaller, meaning 41.7 mm.
      Amount of experience is in direct proportion to the value of broken equipment.

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      • #18
        It was WWII that prompted the adoption of today's thread standards. Prior to that there was an accumulation of thread sizes and pitches. Number screws went up to #30 and fractional started at 1/16". There were a lot of near fits and the standards eliminated and combined many of them.

        Since many items designed and built prior to the standards are still being manufactured, legacy issues result in the continued use of the original threads. This is quite common in the firearms industry as changing midstream would result in repair and replacement confusion. Many of the fasteners used are of a non-standard form, ie small cheese head with large shank or fasteners with shallow engagement such as those for scope mounts, non standard thread forms are used. Fractional threads are still common though not the rule.

        This is not confined to the firearms industry. If you take a look at some of Starret's products, for instance, that have been in production from early on, you will see the same thing.
        Last edited by JCHannum; 07-13-2012, 09:11 AM.
        Jim H.

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        • #19
          For small machine screw sizes, this small chart may help.

          0-80 or .060-80
          1-64 or .073-64
          1-72 or .073-24
          2-56 or .086-56
          2-64 or .086-64
          3-48 or .099-48
          3-56 or .099-48
          4-40 or .112-40
          4-48 or .112-48
          5-40 or .125-40
          6-32 or .138-32
          6-40 or .138-40
          8-32 or .164-32
          8-36 or .164-36
          10-24 or .190-24
          10-32 or .190-32
          12-24 or .219-24
          12-28 or .219-28
          12-32 or .216-32

          Here is a handy chart that probably has everything you need and more.
          http://microadvances.com/drillchart.htm

          George
          Last edited by George_Race; 07-13-2012, 10:52 AM.
          My Web Site
          www.mrrace.com
          Builder & Test Pilot N73EX

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          • #20
            Originally posted by Rich Carlstedt
            Simple.
            There is .013" step increase for each thread over or under .060.
            A 0-80 thread is .060 and may be considered the "base" for all calculations.
            A 1-72 thread is .073 for a major OD ( .060 +.013)
            A 2-56 thread is .086 and so on

            Rich
            I can always remember the .013 step increase. But i can never remember if the .060 starts at #0 or #1
            Lynn (Huntsville, AL)

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            • #21
              Originally posted by lynnl
              I can always remember the .013 step increase. But i can never remember if the .060 starts at #0 or #1
              It's easier if you remember #5 as being .125 nominal.

              Easier for me, anyway. I get .125 and .128 mixed up, too many years in computers.

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              • #22
                Originally posted by Jaakko Fagerlund
                Don't know how it would work with imperial threads, but with metric you can usually shoot for a diameter that is 1/10th of the pitch smaller than the nominal. So for example M42 x 3 would nominally be 42 mm OD, but I would make it 1/10 x 3 = 0.3 mm smaller, meaning 41.7 mm.
                that is true for 12.9 fasteners. a typical 8.8 screw will be smaller. e.g.: 8.000 - 0.125 = 7.875. 8.8 screw will be betwen 7.7 and 7.8. most screws also are tapered, starting with 7.7 and growing to 7.8 towards the head or shank.

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                • #23
                  Originally posted by dian
                  that is true for 12.9 fasteners. a typical 8.8 screw will be smaller. e.g.: 8.000 - 0.125 = 7.875. 8.8 screw will be betwen 7.7 and 7.8. most screws also are tapered, starting with 7.7 and growing to 7.8 towards the head or shank.
                  The bolt strentgth doesn't have anything to do with the major and minor diameters, it is the tolerance class that dictates what the bolt diameters should be. Usual bolts&nuts are 6g/6H class, meaning not ultra precise and not sloppy either, but somewhere in between.

                  The "taper" you describe comes from the thread rolling process itself and is just a side effect and thus not a property.
                  Amount of experience is in direct proportion to the value of broken equipment.

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