Re: Spoke Failure--surface quality or stress relief?

Discussion in 'Cycling Equipment' started by [email protected], Apr 9, 2005.

  1. Rault00 who? writes:

    > And in my experience, the few failures I've seen at the nipple end
    > were clearly due to the spoke being stressed beyond the yield point
    > of the threaded section; the failure was obviously caused by tension
    > in excess of the spoke's load capacity. (I will note that I have
    > yet to see a spoke break at that point without a spokejam being
    > involved, also.)


    I think the picture at:

    http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm

    shows a common failure that occurs at the threads, not caused by the
    mechanisms you mention.

    [email protected]
     
    Tags:


  2. [email protected] wrote:

    > I think the picture at:
    >
    > http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >
    > shows a common failure that occurs at the threads, not caused by the
    > mechanisms you mention.


    That spoke is screwed much too far into the nipple. Possibly the "new"
    thread cut by the nipple created a weak point, as it isn't rolled like a
    proper spoke thread.
     
  3. On Sat, 09 Apr 2005 18:51:42 +0100, Zog The Undeniable
    <[email protected]> wrote:

    >[email protected] wrote:
    >
    >> I think the picture at:
    >>
    >> http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >>
    >> shows a common failure that occurs at the threads, not caused by the
    >> mechanisms you mention.

    >
    >That spoke is screwed much too far into the nipple. Possibly the "new"
    >thread cut by the nipple created a weak point, as it isn't rolled like a
    >proper spoke thread.


    Dear Zog,

    Good eye! Without seeing the other end, we can't tell if the
    spoke was screwed into the nipple past its threads, but it's
    a possibility.

    Come to think of it, how did they fix the spoke for the
    rotation and bending? With no tension, the spoke would
    either have unscrewed when rotated one way, or else screwed
    itself in up to the hilt when rotated the other way.

    Maybe you could fix the spoke in place by adding a second
    nipple as a jam nut to the protruding spoke end?

    Now I'm squinting at that picture again more carefully.

    Do the uppermost two threads of the stump of the spoke look
    as if they've deformed?

    Or is it a trick of the light and whatever they did to cut
    the nipple and show the cross-section?

    Carl Fogel
     
  4. jtaylor

    jtaylor Guest

    "Zog The Undeniable" <[email protected]> wrote in message
    news:[email protected]
    > [email protected] wrote:
    >
    > > I think the picture at:
    > >
    > > http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    > >
    > > shows a common failure that occurs at the threads, not caused by the
    > > mechanisms you mention.

    >
    > That spoke is screwed much too far into the nipple. Possibly the "new"
    > thread cut by the nipple created a weak point, as it isn't rolled like a
    > proper spoke thread.


    Nipples are almost always brass; spokes are almost always steel; care to
    share your experience with brass tools cutting steel?
     
  5. On Sat, 9 Apr 2005 21:31:49 -0300, "jtaylor"
    <[email protected]> wrote:

    >
    >"Zog The Undeniable" <[email protected]> wrote in message
    >news:[email protected]
    >> [email protected] wrote:
    >>
    >> > I think the picture at:
    >> >
    >> > http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >> >
    >> > shows a common failure that occurs at the threads, not caused by the
    >> > mechanisms you mention.

    >>
    >> That spoke is screwed much too far into the nipple. Possibly the "new"
    >> thread cut by the nipple created a weak point, as it isn't rolled like a
    >> proper spoke thread.

    >
    >Nipples are almost always brass; spokes are almost always steel; care to
    >share your experience with brass tools cutting steel?


    Dear J.T.,

    A good comment on sharp observation!

    Sounds as if my question about how fix a rotating and
    bending spoke with its end free is answered--just let it
    turn itself until it jams itself into a brass nipple.

    I like the way that something so apparently simple leads to
    posts like yours and Zog's.

    Thanks,

    Carl Fogel
     
  6. On Sat, 09 Apr 2005 18:51:42 +0100, Zog The Undeniable
    <[email protected]> wrote:

    >[email protected] wrote:
    >
    >> I think the picture at:
    >>
    >> http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >>
    >> shows a common failure that occurs at the threads, not caused by the
    >> mechanisms you mention.

    >
    >That spoke is screwed much too far into the nipple. Possibly the "new"
    >thread cut by the nipple created a weak point, as it isn't rolled like a
    >proper spoke thread.


    Dear Zog,

    Browsing through things again, I realized that the spoke
    broken off in the nipple seems to be just a real-life
    example and not from the actual testing--though it's still
    screwed awfully far into the nipple.

    Here's the example spoke, not from testing (though it's
    natural to assume otherwise):

    http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm

    But the next page in the series mentions that "The spoke
    material is held in a collett and rotated about its long
    axis." And the diagram shows a collett, not a nipple:

    http://www.princeton.edu/~humcomp/bikes/design/desi_19.htm

    And two pages later is a diagram (on the right) showing a
    distance of 0.75 inches from the "grips" (not a spoke
    nipple) to where the spoke is loaded:

    http://www.princeton.edu/~humcomp/bikes/design/desi_21.htm

    So the test used some sort of special holder, not a spoke
    nipple.

    Carl Fogel
     
  7. jtaylor wrote:

    > Nipples are almost always brass; spokes are almost always steel; care to
    > share your experience with brass tools cutting steel?


    I don't know the relative hardnesses of the particular grades of s/s and
    brass used here, but although brass is generally softer, it's not *that*
    much softer. We're not talking about the sort of hardened steel used in
    chains, anyway.

    Now if those spokes I cut out the other day are still in the bin, I'll
    go and screw some of the nipples on really tight and see whether it
    makes new threads.
     
  8. OK, jtaylor is probably right. Forcing a spoke into the nipple leaves a
    faint helical mark on the unthreaded section, but it's not deep enough
    to be called a thread, and probably doesn't weaken it any more than the
    rubbing action of two spokes crossing, which never seems to cause breaks.
     
  9. The Indecipherable writes:

    >> Nipples are almost always brass; spokes are almost always steel;
    >> care to share your experience with brass tools cutting steel?


    > I don't know the relative hardnesses of the particular grades of s/s
    > and brass used here, but although brass is generally softer, it's
    > not *that* much softer. We're not talking about the sort of
    > hardened steel used in chains, anyway.


    > Now if those spokes I cut out the other day are still in the bin,
    > I'll go and screw some of the nipples on really tight and see
    > whether it makes new threads.


    An easy test is to screw a spoke nipple on past the end of the spoke's
    threads and see what it does to the spoke. You'll find that the spoke
    mashed the threads flat in the spoke nipple and leaves no marks on the
    spoke. In the days of tubulars, people regularly used too long a
    spoke and caused this to happen, the spoke nipples being in fairly
    deep sockets beneath the tire base tape.

    [email protected]
     
  10. [email protected] wrote:
    > On Sat, 09 Apr 2005 18:51:42 +0100, Zog The Undeniable
    > <[email protected]> wrote:
    >
    >> [email protected] wrote:
    >>
    >>> I think the picture at:
    >>>
    >>> http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >>>
    >>> shows a common failure that occurs at the threads, not caused by the
    >>> mechanisms you mention.

    >>
    >> That spoke is screwed much too far into the nipple. Possibly the
    >> "new" thread cut by the nipple created a weak point, as it isn't
    >> rolled like a proper spoke thread.

    >
    > Dear Zog,
    >
    > Good eye! Without seeing the other end, we can't tell if the
    > spoke was screwed into the nipple past its threads, but it's
    > a possibility.
    >
    > Come to think of it, how did they fix the spoke for the
    > rotation and bending? With no tension, the spoke would
    > either have unscrewed when rotated one way, or else screwed
    > itself in up to the hilt when rotated the other way.
    >
    > Maybe you could fix the spoke in place by adding a second
    > nipple as a jam nut to the protruding spoke end?
    >
    > Now I'm squinting at that picture again more carefully.
    >
    > Do the uppermost two threads of the stump of the spoke look
    > as if they've deformed?
    >
    > Or is it a trick of the light and whatever they did to cut
    > the nipple and show the cross-section?
    >
    > Carl Fogel


    Carl, they would have had to have taken out the spoke (broken threaded part
    or not) in order to make the cross section of the nipple visible. Thus, how
    do we know they threaded it back into the nipple for the picture exactly as
    far as it was when it was taken out? Thus, we have no idea if the spoke was
    cut by the nipple by overthreading, and that argument is useless.
    --
    Phil, Squid-in-Training
     
  11. On Tue, 12 Apr 2005 16:46:34 GMT, "Phil, Squid-in-Training"
    <[email protected]> wrote:

    >[email protected] wrote:
    >> On Sat, 09 Apr 2005 18:51:42 +0100, Zog The Undeniable
    >> <[email protected]> wrote:
    >>
    >>> [email protected] wrote:
    >>>
    >>>> I think the picture at:
    >>>>
    >>>> http://www.princeton.edu/~humcomp/bikes/design/desi_18.htm
    >>>>
    >>>> shows a common failure that occurs at the threads, not caused by the
    >>>> mechanisms you mention.
    >>>
    >>> That spoke is screwed much too far into the nipple. Possibly the
    >>> "new" thread cut by the nipple created a weak point, as it isn't
    >>> rolled like a proper spoke thread.

    >>
    >> Dear Zog,
    >>
    >> Good eye! Without seeing the other end, we can't tell if the
    >> spoke was screwed into the nipple past its threads, but it's
    >> a possibility.
    >>
    >> Come to think of it, how did they fix the spoke for the
    >> rotation and bending? With no tension, the spoke would
    >> either have unscrewed when rotated one way, or else screwed
    >> itself in up to the hilt when rotated the other way.
    >>
    >> Maybe you could fix the spoke in place by adding a second
    >> nipple as a jam nut to the protruding spoke end?
    >>
    >> Now I'm squinting at that picture again more carefully.
    >>
    >> Do the uppermost two threads of the stump of the spoke look
    >> as if they've deformed?
    >>
    >> Or is it a trick of the light and whatever they did to cut
    >> the nipple and show the cross-section?
    >>
    >> Carl Fogel

    >
    >Carl, they would have had to have taken out the spoke (broken threaded part
    >or not) in order to make the cross section of the nipple visible. Thus, how
    >do we know they threaded it back into the nipple for the picture exactly as
    >far as it was when it was taken out? Thus, we have no idea if the spoke was
    >cut by the nipple by overthreading, and that argument is useless.


    Dear Phil,

    You may be right, but I don't think so.

    The spoke looks as if it broke in two and left most of the
    threaded section in place inside the nipple.

    Then the nipple (still holding the stump of the spoke) was
    ground or cut down to show a cross-section--no removal and
    re-insertion, just a cross-section with the broken spoke
    section in place.

    The stump of the spoke in the example is broken off right
    where I'd expect a spoke to crack at the nipple--just a
    thread into the nipple.

    In any case, this spoke was not part of the actual testing,
    which involved fixing the test spokes in a collett, not a
    spoke--I needed to read further and more carefully in the
    series.

    You can duplicate the basic test quite easily and quickly by
    shoving the threaded end of a spoke into a drill press
    chuck, raising the platform so that the spoke goes through
    the drill hole, and then swivelling the platform to one side
    so that the spoke is bent. Turn the drill on, and the spoke
    will spin, constantly bending, and soon break--how soon
    depends on how much of a bend you put in it.

    The test used a wheel pressing with up to 10 pounds of force
    against the spoke quite close to the chuck (0.75" is shown
    in a diagram). Bending the spoke to one side with the hole
    in the drill press platform is much cruder, even if you oil
    the spot where the spoke revolves against the platform.

    If you take a spoke, bend a small complete loop in its
    middle (a super elbow), and run it through this test, the
    spoke usually breaks in the middle of the loop if you use a
    mild overall bend and wait about five minutes.

    My library has ordered the book for me, so in a month I
    might have the rest of the text.

    Carl Fogel
     
  12. jtaylor

    jtaylor Guest

    <[email protected]> wrote in message
    news:[email protected]
    >
    > You may be right, but I don't think so.
    >
    > The spoke looks as if it broke in two and left most of the
    > threaded section in place inside the nipple.
    >
    > Then the nipple (still holding the stump of the spoke) was
    > ground or cut down to show a cross-section--no removal and
    > re-insertion, just a cross-section with the broken spoke
    > section in place.


    Tricky work, that; cutting the nipple in half, right down to the root of the
    threads, and not touching the spoke...
     
  13. On Tue, 12 Apr 2005 21:13:07 -0300, "jtaylor"
    <[email protected]> wrote:

    >
    ><[email protected]> wrote in message
    >news:[email protected]
    >>
    >> You may be right, but I don't think so.
    >>
    >> The spoke looks as if it broke in two and left most of the
    >> threaded section in place inside the nipple.
    >>
    >> Then the nipple (still holding the stump of the spoke) was
    >> ground or cut down to show a cross-section--no removal and
    >> re-insertion, just a cross-section with the broken spoke
    >> section in place.

    >
    >Tricky work, that; cutting the nipple in half, right down to the root of the
    >threads, and not touching the spoke...
    >


    Dear J.T.,

    D'oh!

    Good eye--I missed that. Now I think that Phil and you are
    right about the stump being removed, the nipple being cut or
    ground, and the stump being reinserted.

    Being wrong about that, I'd better hurry and re-think my
    theory that the spoke would break about one thread down into
    the nipple . . .

    Hmmm . . . I don't think that they'd break off deeper into
    the nipple, well past the beginning of the threads, since
    they'd presumably tear out the nipple's threads.

    But maybe I'm dead wrong about them breaking off a thread
    into the nipples?

    Maybe the spokes tend to break well out of the threaded part
    of the nipple, where the spoke threads end and the smooth
    shaft of the spoke begins? But the maximum stress would seem
    to be right at the spoke-nipple interface, not up above the
    nipple.

    Any thoughts on exactly where the spoke would break on the
    nipple end?

    Carl Fogel
     
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