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  1. #1
    Join Date
    Apr 2018
    Posts
    23

    Threads over 4"

    Hello,

    I am looking for charts for threads over 4", my machinery's handbook only goes up to 4"
    I'm guessing there is a formula for computing the theoretical sizes based on % of thread somewhere.

    But a chart listing all relevant info up to 20" for UN, metric, butress etc. would be nice.

    Any help?

    Thanks!

  2. #2
    Join Date
    Apr 2004
    Posts
    5728

    Re: Threads over 4"

    Are you talking about pitch or diameter?
    Andrew Werby
    Website

  3. #3
    Join Date
    Apr 2018
    Posts
    23

    Re: Threads over 4"

    Quote Originally Posted by awerby View Post
    Are you talking about pitch or diameter?

    I have a 5-8 UN 2B LH thread to do, I plan to thread mill the feature.

    I believe the sizes are 5.000" major 4.8647 Minor 4.9188 pitch diameter.

    I've been supplied the thread gauges to check it, but I always struggle to find the info on threads over 4" so charts would be nice.

    Thanks

  4. #4
    Join Date
    Apr 2018
    Posts
    34

    Re: Threads over 4"

    5-8UN 2B LH:

    5.000" OD

    major diameter 5.000"

    8 tpi means thread pitch is 0.125"

    internal thread bore diameter = 5.000" minus 0.125" = 4.875"

    so bore your part to 4.875" inside diameter.

    thread mill with cutter compensation to 5.000" helically with 0.125" and you're all set.

    Just don't get greedy and do it all in one pass.

    Nice that you have the gauge to check it with...

  5. #5
    Join Date
    Apr 2018
    Posts
    23

    Re: Threads over 4"

    Quote Originally Posted by CaistorAl View Post
    5-8UN 2B LH:

    5.000" OD

    major diameter 5.000"

    8 tpi means thread pitch is 0.125"

    internal thread bore diameter = 5.000" minus 0.125" = 4.875"

    so bore your part to 4.875" inside diameter.

    thread mill with cutter compensation to 5.000" helically with 0.125" and you're all set.

    Just don't get greedy and do it all in one pass.

    Nice that you have the gauge to check it with...
    I would use wear compensation with multiple passes to do this, I came across a page in the machinists handbook that says 4.8647 Minor, are you sure 4.875 wouldn't make the thread loose?
    4.990 is where I plan to begin with wear comp for the Major, and walk it in if the gauge doesn't start.

    I could use 3 wires on the gauge and see where what its pitch diameter is but there has to be some clearance, I'm just perplexed why there isn't more info on threading in the book or doing google searches.
    The part already has a lot of weld fab done to it so I don't want to mess it up now.

  6. #6
    Join Date
    Apr 2018
    Posts
    34

    Re: Threads over 4"

    wear comp with multiple passes - good plan.

    4.990" - good plan.

    I would go for feel with the gauge for the final fit.

    that ten thou on minor isn't really a big deal...on that size of thread, but go with the 4.8647 to make the boss happy..

    May I suggest that on the first pass, bring up your comp radius enough to just kiss the bore id? then you know

    by the marks on the bore that everything is good before going for it.

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