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  • Strength of Buttress Thread

    Apparently there are several buttress thread versions out and about.

    1. Of the various buttress thread versions, which has the greatest axial loading strength?

    2. Is there a thread (designed for axial loading) having greater strength than buttress threads? If so, what.

    Harold
    For those having fought for it, Freedom has a flavor the protected will never know.
    Freedom is only one generation away from extinction.

  • #2
    Originally posted by hwingo
    Apparently there are several buttress thread versions out and about.

    1. Of the various buttress thread versions, which has the greatest axial loading strength?

    2. Is there a thread (designed for axial loading) having greater strength than buttress threads? If so, what.

    Harold
    I made some buttress nuts for a big press break from aluminum bronze. Im sure it good for a few decades.

    1 big freaking threads 6 inch kicks the crap out of 3 inch threads

    2 no see #1

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    • #3
      There's a couple of modified acme and buttress threads that have taken precedence over the plain old buttress in OCTG, but one of the primary considerations on those threads is sealing, not just axial loading.

      Presumably, you're using this for a joint under tension or moving a device? Or are you joining pipe?
      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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      • #4
        my machining book says square threads are the strongest but are difficult to machine. (just reading that this morning in the thrown room)

        Patrick

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        • #5
          Wikkipedia notes that the buttress thread for is asymetric. Has virtually equivalent strength of square in one direction, but less in the other. http://en.wikipedia.org/wiki/Buttress_thread

          Wikkipedia also claims square thread is not as strong as a trapezoidal form http://en.wikipedia.org/wiki/Square_thread_form like Acme http://en.wikipedia.org/wiki/Acme_thread_form, but with different shoulder angles... http://www.roymech.co.uk/Useful_Tabl...apezoidal.html

          At least, that's what Google tells me...
          Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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          • #6
            Originally posted by camdigger
            Presumably, you're using this for a joint under tension or moving a device? Or are you joining pipe?
            I am using this for a joint under tension as well as moving.

            Thanks guys for your replies.

            Harold
            For those having fought for it, Freedom has a flavor the protected will never know.
            Freedom is only one generation away from extinction.

            Comment


            • #7
              In the case of high (make that HIGH) axial loads, the buttress does NOT deflect much. At first blush this can appear as a huge advantage.

              The problem is strain gage testing demonstrates large stress concentration at the root of the thread and the second third and fourth threads do not get the typical shared load.

              Therefore Acme or Trapezoidal with filleted roots, are strong, load sharing, easier to machine, especially with a muti-point tool, and much less likely to suffer a sudden fatigue failure.

              Hth Ag
              Last edited by agrip; 10-23-2009, 02:54 PM.

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              • #8
                So buttress threads are really just cool looking and not good for much else? :P
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                • #9
                  Originally posted by agrip
                  The problem is strain gage testing demonstrates large stress concentration at the root of the thread and the second third and fourth threads do not get the typical shared load. Hth Ag
                  Some firearm locking lugs "appear" to be fabricated using buttress threads. I do believe the breach on some cannons use a buttress thread. My thoughts were on the order of fabricating a bolt and receiver locking lug using butress threads (of course using correct metal). Hearing that the first thread take the major load causes concern.

                  Harold
                  For those having fought for it, Freedom has a flavor the protected will never know.
                  Freedom is only one generation away from extinction.

                  Comment


                  • #10
                    It seem to me that a buttress thread as per DIN 2781 used for hydraulic presses would be a top contender. The thread is 45 deg..
                    Look here about half way down under "S" DIN 2781: http://mdmetric.com/fastindx/t44u.pdf
                    Or here: http://mdmetric.com/tech/stds/din202de.htm

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                    • #11
                      And the size for 'hydrolic press' buttress threads is 100~1100mm according to that page. I bet at that size any thread would do.

                      Can anyone point to an actual tested reason to use buttress threads besides 'they look cool'? and 'look like they should be stronger'?

                      Maybe im just 'thread jaded' after my $600 kurt vise came with what looks to be a standard V threadform (On a 1" or thicker shaft mind you) insted of the allmighty acme that most cheap metalworking vises have (On a 1/2"~3/4" shaft usally mind you..)
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Originally posted by HSS
                        my machining book says square threads are the strongest but are difficult to machine. (just reading that this morning in the thrown room)
                        I would think that acme threads are stronger given the same OD and pitch, since they don't have the stress risers at the interface with the shaft diameter?

                        More importantly, buttress threads are designed to be much stronger in one direction than the other (the direction opposite the saw tooth), which is why they're usually seen on vises, presses and such...
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                        • #13
                          Another factor that gets ignored when assessing threads is that a thread with an angled shoulder will exert a force radially outward when put under load, not just axially.

                          It is not uncommon for this outward force to plastically deform couplings on OCTG if they're over torqued when made up or in use. This is most apparent in OCTG as the connections are often tapered as well....
                          Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                          • #14
                            Hi,

                            I've made ball screws for fly wheel presses up to 100 ton with buttress threads. They are somewhat of a pain to single point as the chip load gets kind of high on the tool. Particularly with 4 pitch threads.

                            I did see an old 4" machinist's clamp that had buttress threads on the screws. The old guy had made it years ago when he was an apprentice. Glass smooth and no play at all even after 30 years of use.

                            I don't recall too well, but didn't Sako or Tikka use buttress threads once for locking the breach of a rifle model?

                            dale
                            If you think you understand what is going on, you haven't been paying attention.

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                            • #15
                              Buttress threads were used on cannon,as suggested earlier. The 16" guns on battleships,and cannon in other applications use buttress threads. Their breeches get very tricky,with the buttress threads cut on several different diameters in the same breech.

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