Newsgroups: rec.bicycles.tech
From: jbrandt@hpl.hp.com (Jobst Brandt)
Subject: Re: Info needed on BICYCLE SPOKES
Date: Mon, 29 Jan 1996 18:47:06 GMT

Rafael Raban writes:

> Any wheel authorities out their have any info on DT
> revolution/competition bicycle spokes or bicycle spoke properties
> and processing in general.  I am working on a project for my metals
> lab comparing processing of various spokes.

I have not used them because I don't work in a bicycle shop where I
might have the opportunity to do so.  I don't use them for my wheels
because I have enough experience with extra thin spokes to not want to
repeat it.  The torsional rigidity of a spoke varies with the fourth
power of the diameter, so you can see that a tenth of a millimeter
makes a large difference.

Not only do <1.5mm diameter spokes twist off relatively easily, but
the 2mm diameter thread has more torque than the appropriate 1.8mm
thread of the same pitch.  This is not a good combination if you don't
use unusual methods for tightening the spokes that, for instance,
unload the spoke at the moment you make the adjustment.  Wheel
building machines can do this.

> If you know of any literature, texts, or if some good company
> literature exists concerning processing of spokes please let me
> know.

DT doesn't talk about their spoke forming machines, nor do they
mention that their spoke wire comes from Sweden.

> I think this may have been the topic of conversation previously, but
> is it the elbow on DT Revolution spokes that is forged?

The entire spoke is formed cold from continuous wire.  The elbow is
probably the crudest part in that it is knocked over to one side as
the last operation, merely by bumping it on the side of the head with
a measured glancing blow.

Jobst Brandt      <jbrandt@hpl.hp.com> 

Newsgroups: rec.bicycles.tech
From: jbrandt@hpl.hp.com (Jobst Brandt)
Subject: Re: Info needed on BICYCLE SPOKES
Date: Sat, 3 Feb 1996 02:20:04 GMT

J. Lee writes:

> DT proudly says that they use Swedish steel for their Revolution
> spokes (in the product flyer).

I wasn't aware of that.  Previously that was not mentioned.  Do they
just say Swedish steel or that the finished wire comes from Sweden?
The wire and DT's swaging process are the essence of their spokes.
The other operations are done the same way anyone else does them.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: DT Revolution spokes
Date: 26 Nov 1996 03:13:25 GMT

Rafael Raban writes:

> Yes, it is interesting what part of the spoke broke?  I sectioned some DT
> Revolution spokes both longitudinally and transversely, etched the surface to
> reveal the microstructure and found some interesting stuff in the swaged
> section.

> It turns out that the swaging process is so severe (2mm --> 1.5 mm) that you
> get a "spiral" type texture looking at the transverse section.  This is the
> result of repeated elliptical deformations of the spoke.

> At the very center of the spiral, cracks form (~0.1 - 0.2 mm wide) oriented
> longitudinally and run the entire length of the swaged section.

What this suggests is that not only is such a reduction undesirable because
the torsional strength is to little to properly tension the spoke, but that
the reduction is more than the material will withstand in cold working.  It's
good to know that there is more than one reason not to do this.

I has been my experience with spokes of this diameter ration that were
made by Berg and Radiali, among others, broke explosively while
tightening them.  The combined stress of tension and thread torque was
enough to make them fail.  With longitudinal cracks, the torsional
strength is further compromised. I have held off using these spokes
because I didn't trust their integrity.  Your analysis reinforces my
doubts.

> Given the orientation of the crack, I would say it will not lead to
> failure of the spoke.  Perhaps people who have experienced failures
> can comment...  However, the mere fact that the cracking is there is
> surprising given DT's reputation. It seems that DT should improve
> their processing.

Having been at their plant and talking to those in charge, I get the
impression that there are no R&D engineers there any more.  The spoke
manufacture is mainly in the hands of marketing as I see it and that
can lead to poor decisions such as these ultra thin spokes and the
super fat MTB spokes with a small thread at the end.

From incoming wire, I could see that they were using Swedish steel.  I
wondered why the Swedes don't just keep the wire at home and make
spokes.

Jobst Brandt      <jbrandt@hpl.hp.com> 

Subject: Re: DT Revolution spokes
From: rmr3@Lehigh.EDU
Date: Nov 28 1996
Newsgroups: rec.bicycles.tech

Jobst Brandt writes:
>
>> The "manufacturing techniques and materials" to produce good quality
>> swaged spokes have been around for quite some time.  If the spokes
>> were annealed at some point during the swaging process, DT would
>> easily solve their problems while maintaining the "spiral" type
>> mechanical fibering which is generally beneficial.
>
>I think that if you were to reconsider that suggestion or be familiar
>with the manufacture of spokes, you would retract that statement.
>Much of the strength of these spokes is achieved by cold working.  I
>believe that DT has exceeded the cold working possible with their
>method in reducing a 1.8mm wire to 1.45mm diameter.  I base that on
>the cracking that was visible in the sample mentioned.  I suspect that
>the helical patterning is only an artifact of the swaging rollers.
>
>Jobst Brandt      <jbrandt@hpl.hp.com>


Jobst, your last statement is correct, but the fact of the matter is that heat
treatments above the recrystallization temperature of a material are essential
in any cold working deformation process.  The drawing of the spoke wire for
example requires several recrystallization annealing treatments otherwise
cracking commonly known as "burst" occurs as the wire is reduced.

If you were to examine the microstructure of the spokes (oriented
longitudinally) to your surprise, you will not find much mechanical fibering
characteristic of cold working processes (drawing).  The grains, in fact, are
fairly equiaxed.  In addition, annealing twins dominate the structure which
provides evidence of recrystallization after cold working.

So in regard to the swaging process, my suggestion was that the spokes be
annealed at some point during this process to prevent excessive cold working
of the material which leads to cracking.

As for the strength of the spokes, I am sure you know that this is not a
critical property in this case since spokes almost always break in fatigue.
In fact, you may not always want a higher strength since this also results
in decreased fracture toughness and thus a shorter fatigue life.

-Rafael

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: DT Revolution spokes
Date: 1 Dec 1996 02:57:11 GMT

Rafael Raban writes:

>> I think that if you were to reconsider that suggestion or be familiar
>> with the manufacture of spokes, you would retract that statement.
>> Much of the strength of these spokes is achieved by cold working.  I
>> believe that DT has exceeded the cold working possible with their
>> method in reducing a 1.8mm wire to 1.45mm diameter.  I base that on
>> the cracking that was visible in the sample mentioned.  I suspect that
>> the helical patterning is only an artifact of the swaging rollers.

> Jobst, your last statement is correct, but the fact of the matter is
> that heat treatments above the recrystallization temperature of a
> material are essential in any cold working deformation process.  

I draw my conclusions from the spokes I tested.  For the first edition
of my book I found that DT spokes broke in the fat (unaltered) part of
the spoke, not in the swaged segment, in tensile testing.  This I
attributed to the additional drawing or rolling during the swaging
process that hardened that zone.  A few years later, I tested similar
spokes and found that they ruptured in the swaged sections and at a 
higher stress than the earlier ones, besides having more elongation.

From this it can be deduced that the wire now comes fully work
hardened and cannot take much additional drawing without annealing
that would adversely affect the strength of the un-swaged section.
Besides, annealing spokes in process would make the whole process
unbearably expensive for no purpose.  The conventional DT 1.8-1.6mm
swaged spokes are so durable that after proper wheel building, they
last practically forever.  I have a set of wheels that have far
more than 100000 miles on them and many rim replacements.

> So in regard to the swaging process, my suggestion was that the
> spokes be annealed at some point during this process to prevent
> excessive cold working of the material which leads to cracking.

Again, if you saw the process from wire reel to spoke box, I think
you would not consider annealing a practical option.  There is no need
for 1.8-1.5mm spokes.  As I said, there seems to be no one home in the
engineering department.  That's why they made 2.4mm MTB spokes with a
2mm x 56 TPI end to fit conventional rims and nipples.

> As for the strength of the spokes, I am sure you know that this is
> not a critical property in this case since spokes almost always
> break in fatigue.  In fact, you may not always want a higher
> strength since this also results in decreased fracture toughness and
> thus a shorter fatigue life.

It is critical, because tensioning spokes highly stresses them in
torsion.  Because thin spokes less than 1.6mm in diameter already pose
a rupture problem, thinner spokes and ones with longitudinal
fractures, will snap before reaching any useful tension.  Besides,
with the emphasis on few spokes, tensions must automatically be higher
to support the same load.  It doesn't work.

Jobst Brandt      <jbrandt@hpl.hp.com>