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More on Slack Spokes



 
 
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Old July 20th 19, 04:13 AM posted to rec.bicycles.tech
jOHN b.
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Default More on Slack Spokes

On Fri, 19 Jul 2019 21:16:53 -0500, AMuzi wrote:

On 7/19/2019 8:53 PM, John B. wrote:
On Fri, 19 Jul 2019 19:10:18 -0500, AMuzi wrote:

On 7/19/2019 6:29 PM, John B. wrote:
On Fri, 19 Jul 2019 08:15:31 -0500, AMuzi wrote:

On 7/19/2019 2:17 AM, John B. wrote:
On Thu, 18 Jul 2019 21:50:50 -0700 (PDT), Chalo
wrote:

John B. wrote:
And when you fouled a few threads, you actually foul all the threads
that are engaged which if the spoke end protruded through the nipple
is effectively all the threads.

No, that's not true. Remember that the hard stainless spoke threads are unaffected; only the few brass threads that run up on the unthreaded shank are distorted. Since there are many turns of thread inside the nipple, those can serve as a lock while the rest function normally. It's analogous to an all-metal locknut that has been staked to distort the thread slightly on one end.

I see, or maybe I don't see, but I think that what you mean is that
when the threads in a stainless spoke/brass nipple assembly are
damaged only the threads in the brass nipple are damaged, because it
is the softer material. Which is certainly true... but if the threads
in the brass nipple are damaged isn't the strength of the threaded
joint diminished?

Carry it to an extreme and tighten the joint a bit more and as you
say, only the threads in the brass nipple are damaged , but isn't
strength of the joint reduced? After all the damage to the threads is
that they are partially sheered from the parent material and another
turn or two the threads will be completely sheered from the brass
nipple and the strength of the joint will become zero.


I'm with Chalo on that:
http://www.yellowjersey.org/NIPPLES.JPG

2 or 3 turns work as he described. Ten turns would be as you
predicted.

Assuming that you start with sufficient torque to ensure that the
threads on the "screw" are firmly pressed against the threads in the
"nut" than any further torque must either stretch the screw outside
the nut or damage the threads by at least partially sheering the
threads in either the screw or the nut.

And that is not just me talking. Read any engineering book about
threads and torque. You can also test it yourself. Clamp a hex headed
bolt in a vise. Stack sufficient flat washers on the bolt to ensure
that the nut will not bottom out on the bolt threads, tighten the but
to the designated torque for that bolt/nut combination. Now turn the
nut 3 more revolutions.
--
cheers,

John B.


Yes, that's well known.

In the case of a stainless spoke with a brass nipple, the
unthreaded spoke body is half-height of the raised rolled
hard thread and the brass nut is soft. I didn't theorize
about it, I observed it in multiple iterations. As has
Chalo, I assume.


What are you saying? that the nipple threads being of a larger
diameter than the necked down portion of the spoke will screw right
off the enlarged end of the spoke that is threaded and move freely
along the necked down portion of the spoke? I can accept that, in fact
I have some spokes that were shortened and rethreaded by a shop in
Singapore that are exactly like that.
--
cheers,

John B.


Well, yeah, sorta.

The brass thread is still deformed because the root of the
spoke thread ended. Some proportion of the nipple thread is
pushed. Which, as noted by Chalo, becomes effectively, a
threadlocker.


O.K. I see what you mean. In essence you are forfeiting a number of
threads that might be contributing to the strength of the threaded
nipple/spoke joint to act as a thread locking device.

Well, as an aside, aircraft have many of the same considerations as
bicycles notably weight versus power considerations but doubt that
any aircraft inspection agency in the world is going to encourage
jamming and crushing threads as a viable thread locking device :-)

Which is, I realize is neither here not there, so lets just leave it
that some, like electric shifting and chain lube, think one way is
best while others think just the opposite. :-)

In practice, a few threads like this behave like a nylock
nut until, at some high proportion of damaged thread, it's
just a ruined fastener.


:-) Well not exactly as the nylon nut still has the required number
of metal threads to be capable of withstanding the specified load for
that size bolt, which are not distorted by tightening the nut.
--
cheers,

John B.

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