Minimum Spoke Thread Engagement

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Andrew Muzi writes:

>>>> In a previous discussion on this, several posters were very
>>>> certain that longer nipples gave no extra thread so I expect that
>>>> is true of some brands.

>>> I'm not arguing, but I am very puzzled. What would be the reason
>>> for making nipples taller without bringing the thread all the way
>>> to the top?

>> I have plenty of 25.4mm long spoke nipples formerly used for wood
>> rims. These have about as many threads at the head end as current
>> shorter nipples have and have a smooth bore to the end with the
>> spoke wrench flats. As I see it, the intent is to not have the
>> brass nipple bear the spoke load in tension. Cutting a deep thread
>> also costs more (time) and offers no advantage, assuming the wheel
>> is built with the proper parts.

>> Another reason for this might have come from times when spokes had
>> cut instead of rolled threads so that engagement beyond the end of
>> the thread was not possible because it would bind on the unthreaded
>> part of the spoke that was the same diameter as the major thread
>> diameter.

> I truly do not know. When were spoke threads cut? Rolled threads
> (Cyclo thread rolling machine) go back to at least the fifties.

Wood rims went out with WWII so the 1950's is past their time. The
stuff I have was probably from the 1920's and 30's. Old stock, the
rest of which was probably junked shortly after I got some of it.

These one inch spoke nipples were probably from the USA anyway, even
though I got them in CH. That's probably why they are 1" long.

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[Jim Adney]

On Mon, 21 Mar 2005 21:07:09 GMT [email protected]
wrote:

>Another reason for this might have come from times when spokes had cut
>instead of rolled threads so that engagement beyond the end of the
>thread was not possible because it would bind on the unthreaded part
>of the spoke that was the same diameter as the major thread diameter.

But such binding occurs with rolled threads also.

-
-----------------------------------------------
Jim Adney [email protected]
Madison, WI 53711 USA
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Jim Adney writes:

>> Another reason for this might have come from times when spokes had
>> cut instead of rolled threads so that engagement beyond the end of
>> the thread was not possible because it would bind on the unthreaded
>> part of the spoke that was the same diameter as the major thread
>> diameter.

> But such binding occurs with rolled threads also.

I think you'll find that you can run right past the end of thread
without much trouble, although it isn't doing the overrun threads any
good. In the days of tubulars I often got wheels that had about 3mm
of spoke protruding out of the spoke nipple. It gets done often even
now.

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[Jim Adney]

On Wed, 23 Mar 2005 03:20:24 GMT [email protected]
wrote:

>Jim Adney writes:
>
>>> Another reason for this might have come from times when spokes had
>>> cut instead of rolled threads so that engagement beyond the end of
>>> the thread was not possible because it would bind on the unthreaded
>>> part of the spoke that was the same diameter as the major thread
>>> diameter.
>
>> But such binding occurs with rolled threads also.
>
>I think you'll find that you can run right past the end of thread
>without much trouble, although it isn't doing the overrun threads any
>good. In the days of tubulars I often got wheels that had about 3mm
>of spoke protruding out of the spoke nipple. It gets done often even
>now.

It's clear that the binding would have to be less with the rolled
threads. I just never felt comfortable forcing a nipple past that
point of first binding. I'm sure it can be done: I just never thought
of it as a worthy practice (and I suspect that you'd agree.)

BTW, I agree completely with your first reason: that of keeping the
nipple in compression rather than tension.

-
-----------------------------------------------
Jim Adney [email protected]
Madison, WI 53711 USA
-----------------------------------------------

 

[B.C. Cletta]

jim beam wrote:
> bigsky wrote:
> > I'm building a wheel using a rim with no official source of
dimensions
> > (Mavic Rimtec 190FB). I measured the effective rim diameter and
fed
> > this and selected Campy 10 speed hub (Centaur) into the DT Swiss
> > calculator. I also did the calculations by hand as a double check,
and
> > they agreed (292mm/294mm). However, it seems the numbers come out
> > slightly short. I had trouble getting all the spokes to engage the

> > nipples during cross (3) and now with all spokes engaged but not
> > tensioned, I count about 5 turns. I estimate that I have about
2.3mm of
> > thread engagement, but it does not look like I will get full thread

> > engagement to where the spoke is flush with the nipple end. Will
this
> > be enough thread engagement to ensure full strength? I would like
to be
> > sure before I tension and set the spokes in the new hub.
> >
> > Thanks,
> > bigsky
> >
> as far as mechanical strength is concerned, you only need 3 threads.

this is the textbook answer. the real world answer is 5, 3 + 2 in
case any of the 1st three fail (66% safety factor). count the number
of threads in any std nut.

> as
> far as vibratory loosening is concerned however, you need a few more.

> spokes also traditionally have more thread engagement for ease of
build
> and any subsequent adjustment. with this in mind, i'd be inclined to

> get a new set of spokes & rebuild.

i'm not too keen on this. if the other threads aren't loaded
(because the 1st three are carrying the load), they could not provide
any vibration resistance.
also, according to TBW, a spoke will grow about 1-mm under load so
you'll pick-up two turns.
me? if i had what you said you have, i'd finish the build.
oh yeah, you can check the ERD by measuring the drop from the bead
diameter, 622 for 700c, to the spoke bed: ERD= 622 - 2x[drop]

 

[Martyn Aldis]

In message <[email protected]>, B.C.
Cletta <[email protected]> writes
>jim beam wrote:
>> as far as mechanical strength is concerned, you only need 3 threads.
>
> this is the textbook answer. the real world answer is 5, 3 + 2 in
>case any of the 1st three fail (66% safety factor). count the number
>of threads in any std nut.
>

How many threads are involved depends on the elasticity and cross
sectional areas of nut and bolt. As the brass nipple is more elastic
than the spoke and it's cross section is less than a standard nut the
threads involved in load transfer must be higher than for a standard
nut/bolt interface.


--

Martyn Aldis, e-mail [email protected]
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