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Thread: 31/32", 30 TPI; what manner of wacky thread is this?

  1. #31
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    Quote Originally Posted by old mart View Post
    I fail to understand why some people try to equate an old fraction size, however obscure, with metric sizes. I would bet that the original designer didn't.
    Really, well let us know how many 32nd sizes you have run across, or worked with.
    The first thing I do when I measure a major diameter is try to match it up with a nominal size.
    Major dia tends to usually be undersize.


    As far as my 25mm guess, I had forgotten he had an actual marked die.

  2. #32
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    Quote Originally Posted by Toolguy View Post
    It was probably used in the making of the Millenium Falcon in Star Wars to a standard that doesn't exist yet.
    Thanks everyone for your very interesting replies. This suggestion is the most probable, however. Corellian Engineering Corp specified 7/8" UNF fasteners throughout much of the construction of the YT-1300 models, especially where bulkheads were mated in the joining of modular sections in the final stages of chassis assembly. It would make sense, given the increased inertial stresses and gravimetric shear introduced by the performance modifications added to the Falcon, that an upgrade to structural components was needed as well. It seems Han Solo specified 31/32-30 as the particular threadform for the job, although testing was less than scientific, and was mostly done through "seat of the pants" intuition, as was the customary approach to spaceflight a long time ago in a galaxy far far away.

    Here are some pics of it in it's unusual die stock:



  3. #33
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    Quote Originally Posted by Richard P Wilson View Post
    A special certainly, possibly for a locking nut thread on a 1" shaft, so a bearing race or seal could pass easily over the thread? Just guessing.
    That sounds like a good, and educated guess. Perhaps so old it predates the 32 TPI standard.

  4. #34
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    Some guy with an old car has been searching the internet for 2 years for a bolt to fit that die.

  5. #35
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    Quote Originally Posted by kendall View Post
    Some guy with an old car has been searching the internet for 2 years for a bolt to fit that die.
    Help me, some guy with an old car! You're my only hope!

    I've got quite a lot of old dies and stocks. Most of it standard, although older than some things I've seen in museum collections. Tools is tools as long as they're useful. I'd like to think this is still useful to someone so I hope you're right. Someone with an old something may yet appear to prove this die useful once more.

  6. #36
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    I once specified a 3-41/64" x 16 tpi thread to solve an engineering problem.
    The problem was some internal threads in some fiberglass tubes.
    The thread used to be 3-5/8" x 16 with a specific pitch diameter and major
    and minor diameters. Trouble was, even after I spelled these sizes out on
    the print, (to help save a lazy machinist from doing the math), the threads
    would continue to come in undersize.
    So since the machinist would hold on to the thread call-out and would ignore
    the actual pitch diameter and major/minor numbers, I was forced to invent
    the 3-41/64"-16 thread size.
    Now the machinist realized something was up when he saw that. Seeing the
    odd size was a wake up and pay attention call, and low and be hold, I got my
    threads to the size I wanted. Bizarre as it was, the odd thread call-out was
    more of a human psychology trick than an actual engineering necessity.
    The goal actually was a 3-5/8" x 16 thread size, with a loose class 1 fit to make
    room for putting epoxy in the threads. Even providing the numbers, I could not
    get the vendor to make this class 1 loose fit, so I invented the odd thread.
    I would have never thought a bastard thread would ever to be invented to
    deal with a humans reluctance to pay attention to the drawing, but I actually
    did this in real life. You can't make this stuff up.

    --Doozer

  7. #37
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    Thank heavens Excellent has posted pictures of the actual die, confirming that it is NOT METRIC!

  8. #38
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    I could see an odd size like that being used for something like a proprietary metal banister railing, although it sounds like the previous deduction is much more likely.

    1/2" x 12 was a common size around 1900. I have an old 6hp engine from that era which uses that size for head studs and various other bolts.

    FWIW, many of the different diameter fasteners used on the early Wright Brothers engines had 20 threads per inch, presumably because they were cut (single-pointed) on their change-gear lathe, and changing gears for a different ration wasn't considered necessary.

    .
    Last edited by CreakyOne; 06-01-2018 at 04:48 PM.

  9. #39
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    Quote Originally Posted by CreakyOne View Post
    FWIW, many of the different diameter fasteners used on the early Wright Brothers engines had 20 threads per inch, presumably because they were cut (single-pointed) on their change-gear lathe, and changing gears for a different ration wasn't considered necessary.

    .
    Wasn't constant pitch bolts also used in early HD motorcycles?
    There is still standard for them, for example 16tpi: http://www.efunda.com/designstandard.../screw16un.cfm

  10. #40
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    Quote Originally Posted by old mart View Post
    Thank heavens Excellent has posted pictures of the actual die, confirming that it is NOT METRIC!
    The maker probably didn't have any metric stamps, so he substituted the imperial measurement.

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