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Thread: What's the application of 5/16 40tpi tap

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    lowCountryCamo's Avatar
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    Default What's the application of 5/16 40tpi tap

    I bought a box of tooling from an old machinist. In that I found a 5/16 by 40 tpi. Is there a special application of a tap that size? Maybe for chasing mic treads or some such?

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    J Henricksen is offline Stainless
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    The screw in my small boring head has a 5/16-40 thread. Make a spare nut for one if you needed
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    5/16" x 40 is a model emgineering (ME) thread in UK
    It was designed a long time ago to put a thread in thin wall tubing .
    It comes in a whole pile of sizes . and there are also 32 TPI in the ME range .
    The range is from 1/8" right up to 1/2"

    ME Tapping Drills Chart | Drill Sizes | Model Engineer Thread

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    Smrtman5 is offline Cast Iron
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    IIRC an inch mic thread is 1/4-80. Theres a lot of fun threads out there, i found a couple of .570 -32 in a drawer at work. I dont know any specific uses for a 5/16-40 tho.

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    Quote Originally Posted by Smrtman5 View Post
    IIRC an inch mic thread is 1/4-80. Theres a lot of fun threads out there, i found a couple of .570 -32 in a drawer at work. I dont know any specific uses for a 5/16-40 tho.
    That pitch would render a rather strange micrometer barrel: .0125 advance per full revolution. Maybe you were thinking 1/4-40?
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    kenh is offline Titanium
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    5-40 tpi shows up in gun cleaning rods, also a 7-32.
    Remington has used 30 tpi.
    I made a 9/32- 30 screw for a gun smithe buddy.

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    jim rozen is offline Diamond
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    Electronics parts have threads of that flavor.

    Connector threads, switch barrel threads, etc.

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    stephen thomas is offline Diamond
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    I just made a bunch of locks for a specialty application that had combination keys. The mic barrels on the keys were 1/4" - 40. 'Course that was my choice. I'll speculate that a 40tpi tap is just often chosen for "special" apps where the maker/designer wants to control motion or position in a very small increment that is familiar, like the common micrometer thread; and not too much force is required.

    smt

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    Quote Originally Posted by lowCountryCamo View Post
    I bought a box of tooling from an old machinist. In that I found a 5/16 by 40 tpi. Is there a special application of a tap that size? Maybe for chasing mic treads or some such?
    If the "old machinist" hasn't passed, you might ask him. Could be for an interesting application none of us would think of...

    Regards,
    --Lee
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    CalG is offline Titanium
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    40tpi does lend it's self to "micrometer" type application. With each turn of the screw effecting a .025" translation.

    Something we all should be quite familiar with...Unless one has never looked past the LCD display ;-)

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    James H Clark is offline Hot Rolled
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    Instrument makers. Years ago, I bought at auction a small box of oddball taps that came from an instrument company. Most of them were extrafine threads.

    JH

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    I have seen it on some medical stuff and also on some types of magnetic sensors.

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    ....and a differrential screw having both a right hand 40TPI and a left hand 25TPI, gives an advancement of 0.001" per revolution.

    Mark the dial with 200 increments, (or mic barrel with vernier) for 0.000005". Requires a steady touch if you expect repeatability...........

    Bob
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    stephen thomas is offline Diamond
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    ....and a differrential screw having both a right hand 40TPI and a left hand 25TPI, gives an advancement of 0.001" per revolution.
    I use differential screws for the adjusters on my (woodworking) planes. The inherent problem with a differential screw is how much space or displacement of two of the components together is required for any sort of distance travel of the third. In your example, in 25 turns, one component would move into another 1 inch, which moving out of the third 5/8" (25/40"); or IOW carrying the traveler 3/8" in 25 turns or .015"/rev. Effective tpi 66.66.

    So, to carry a traveler a full inch of travel, the 25tpi section needs to be nearly 3" long and the 40 tpi section almost an additional 2" (15/8"). If you get down to .001/ rev resolution, the component threads get quite long to have the option of moving a traveler say 1".

    Edited: My example assumes both threads the same hand, for differential motion. Bob, I just re-read your spec, one LH and the other RH and as far as the cases I can come up with, this would be a compound thread leading to 1-5/8" displacement of the traveler in one direction with 25 turns. Effectively 15.385 tpi. But again, most of the mechanical arrangements I've considered were to effect differential motion in the stem of a wood plane adjuster. So there may be mechanical options I have not considered. I know you are a whizz at some of this stuff, so a diagram might help.

    smt
    Last edited by stephen thomas; 07-07-2013 at 07:09 PM.

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    spope14 is offline Stainless
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    measurement applications. Thought it may be a glow plug tap for larger engines, but not sure now.

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    gmatov is offline Diamond
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    Lot of ado about nothing. You can't say "This thread is useful, this one is not." You are not the Head Mother Fucker in Charge.

    Corps used to come up with proprietary threads, after they standardized.

    I have, I think, a 128 TPI tap. Feels like a poorly finished turning. But it is indeed a tap. Was there a need for it? Obviously there was, or it would have never been made. It HAS been used mre than once, so, once upon a time, it was useful, and possibly even a standard size. For what, I don't know.

    That there IS such is proof that there WAS a need . It is not a one off.

    George

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    hickstick_10 is online now Stainless
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    Getting great wifi from that bar stool I see
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    Here's some modern examples of the fine stuff: Thorlabs - Adjustment Screws . They're used a lot on mirror mounts and the like where you can get very fine accuracy because you're perturbing an laser beam or something at an angle. For optical scale direct movements you need differential threads or some fancy flexure thingy. They have the taps too: Thorlabs - Drill and Tap Kits

    RC
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    Smrtman5 is offline Cast Iron
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    Quote Originally Posted by aerodark View Post
    That pitch would render a rather strange micrometer barrel: .0125 advance per full revolution. Maybe you were thinking 1/4-40?
    Haha, youre absolutely right, that would make for a funny micrometer. I sure hope i was thinking 1/4-40 lol

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    In an LCSmith double barrel shotgun there is a replaceable firing pin bushing that has that thread. Only time I have ever used it.

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