Dark bands on 15g spokes

[Bbb]

I just spotted something interesting while building my first wheel (thank you JB for an enlightening
read) and I was wondering if there is a term for the phenomenon.

I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing the
wheel to proper tension and true, I noticed that most of the spokes on the left side of the wheel
had a periodic pattern of alternating dark and light bands along the spoke. Each band was about 5mm
in length. I then looked much more closely at the spokes on the right side; I noticed that some of
them had similar bands but they were very faint. The left spokes were manufactured by Wheelsmith and
the right spokes by DT.

The effect reminds me a little of "shear banding". Shear banding occurs when elastic materials are
so stressed that they start to undergo plastic deformations. The spoke tensions in my wheel don't
seem that high: tensions on the left are around 60kgf (egad, who IS responsible for that unit?) and
on the right about 125kgf.

So, tell me. Should I ride on this thing or what?

 

[Jobst Brandt]

Birk Brat who? writes:

> I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing the
> wheel to proper tension and true, I noticed that most of the spokes on the left side of the wheel
> had a periodic pattern of alternating dark and light bands along the spoke. Each band was about
> 5mm in length. I then looked much more closely at the spokes on the right side; I noticed that
> some of them had similar bands but they were very faint. The left spokes were manufactured by
> Wheelsmith and the right spokes by DT.

I've never seen the effect and can't imagine what causes it. Could it be that something in packaging
transferred a pattern on the spokes. That spokes from different manufacturers have the same pattern
is odd. It suggests that the coloring came after the spokes were out of the package. I can't imagine
that it is stress related.

You didn't make a good explanation of the appearance. How regular is the pattern among spokes and
can it be polished away with a moist rag and Bon Ami household cleanser?

> The effect reminds me a little of "shear banding". Shear banding occurs when elastic materials are
> so stressed that they start to undergo plastic deformations. The spoke tensions in my wheel don't
> seem that high: tensions on the left are around 60kgf (egad, who IS responsible for that unit?)
> and on the right about 125kgf.

It seems you know more about this than I, so I'll defer on offering a stress related cause.

> So, tell me. Should I ride on this thing or what?

Why not?

Jobst Brandt [email protected] Palo Alto CA

 

[Mark Hickey]

[email protected] (BBB) wrote:

>I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing the
>wheel to proper tension and true, I noticed that most of the spokes on the left side of the wheel
>had a periodic pattern of alternating dark and light bands along the spoke. Each band was about 5mm
>in length. I then looked much more closely at the spokes on the right side; I noticed that some of
>them had similar bands but they were very faint. The left spokes were manufactured by Wheelsmith
>and the right spokes by DT.

Are you building the wheel next to a window with mini-blinds per chance? ;-)

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Bbb]

[email protected] wrote in message news:<[email protected]>...
> Birk Brat who? writes:
>
> > I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing
> > the wheel to proper tension and true, I noticed that most of the spokes on the left side of the
> > wheel had a periodic pattern of alternating dark and light bands along the spoke. Each band was
> > about 5mm in length. I then looked much more closely at the spokes on the right side; I noticed
> > that some of them had similar bands but they were very faint. The left spokes were manufactured
> > by Wheelsmith and the right spokes by DT.
>
> I've never seen the effect and can't imagine what causes it. Could it be that something in
> packaging transferred a pattern on the spokes. That spokes from different manufacturers have the
> same pattern is odd. It suggests that the coloring came after the spokes were out of the package.
> I can't imagine that it is stress related.
>
> You didn't make a good explanation of the appearance. How regular is the pattern among spokes and
> can it be polished away with a moist rag and Bon Ami household cleanser?

The dark bands are discolorations in the steel of the spoke; they were not there before the wheel
was built and they cannot be easily polished off now. The pattern is striking. A segment of the
spoke about 5mm in length will be discolored followed by a segment of the spoke, also about 5mm in
length, that is not discolored. The alternating bands of dull and bright steel run along the entire
spoke, from the nipple to the hub. Although there are variations in the pattern (some bright
segments are long) I would say that overall it is very regular.

The only thing that might be unusual was that as the wheel was built, the left side was uniformly
overtensioned by about 50% and then relaxed to normal tension once I understood the error.

Oh well. I guess I'll ride the thing 'till the spokes start poppin'.

 

[Robin Hubert]

"BBB" <[email protected]> wrote in message
news:[email protected]...
> [email protected] wrote in message
news:<[email protected]>...
> > Birk Brat who? writes:
> >
> > > I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing
> > > the wheel to proper tension and true, I noticed that most of the spokes on the left side of
> > > the wheel had a periodic pattern of alternating dark and light bands along the spoke. Each
> > > band was about 5mm in length. I then looked much more closely at the spokes on the right side;
> > > I noticed that some of them had similar bands but they were very faint. The left spokes were
> > > manufactured by Wheelsmith and the right spokes by DT.
> >
> > I've never seen the effect and can't imagine what causes it. Could it be that something in
> > packaging transferred a pattern on the spokes. That spokes from different manufacturers have the
> > same pattern is odd. It suggests that the coloring came after the spokes were out of the
> > package. I can't imagine that it is stress related.
> >
> > You didn't make a good explanation of the appearance. How regular is the pattern among spokes
> > and can it be polished away with a moist rag and Bon Ami household cleanser?
>
> The dark bands are discolorations in the steel of the spoke; they were not there before the wheel
> was built

or perhaps you just didn't notice them? Not that I could figure it out, but there are plenty of
smart guys here that are as capable as any.

>and they cannot be easily polished off now. The pattern is striking. A segment of the spoke about
>5mm in length will be discolored followed by a segment of the spoke, also about 5mm in length, that
>is not discolored. The alternating bands of dull and bright steel run along the entire spoke, from
>the nipple to the hub. Although there are variations in the pattern (some bright segments are long)
>I would say that overall it is very regular.
>
> The only thing that might be unusual was that as the wheel was built, the left side was uniformly
> overtensioned by about 50% and then relaxed to normal tension once I understood the error.
>
> Oh well. I guess I'll ride the thing 'till the spokes start poppin'.

Got a camera and way of posting pic's on the web?

Robin Hubert

 

[Jobst Brandt]

Robin Hubert writes:

> Got a camera and way of posting pic's on the web?

As scanner will do that pretty well. I've sent pictures of hardware thicker than a pocket knife
using a simple page scanner. Maybe we can learn more about this with more than 10,000 words, aka
a picture.

Jobst Brandt [email protected] Palo Alto CA

 

[John Albergo]

BBB wrote:

>
>
>The dark bands are discolorations in the steel of the spoke; they were not there before the wheel
>was built and they cannot be easily polished off now. The pattern is striking. A segment of the
>spoke about 5mm in length will be discolored followed by a segment of the spoke, also about 5mm in
>length, that is not discolored. The alternating bands of dull and bright steel run along the entire
>spoke, from the nipple to the hub. Although there are variations in the pattern (some bright
>segments are long) I would say that overall it is very regular.
>
>
>
>
The only thing that comes to mind is spoke twist. Are these bands concentric or do they form a
spiral pattern as they go around the spoke? I've seen light and dark bands when twisting a
paper-clip, for example. But I've never twisted a spoke that badly; it would take quite a few twists
to get a 5-mm pattern!

 

[Bbb]

John Albergo <[email protected]> wrote in message news:<[email protected]>...
> BBB wrote:
>
> >
> >
> >The dark bands are discolorations in the steel of the spoke; they were not there before the wheel
> >was built and they cannot be easily polished off now. The pattern is striking. A segment of the
> >spoke about 5mm in length will be discolored followed by a segment of the spoke, also about 5mm
> >in length, that is not discolored. The alternating bands of dull and bright steel run along the
> >entire spoke, from the nipple to the hub. Although there are variations in the pattern (some
> >bright segments are long) I would say that overall it is very regular.
> >
> >
> >
> >
> The only thing that comes to mind is spoke twist. Are these bands concentric or do they form a
> spiral pattern as they go around the spoke? I've seen light and dark bands when twisting a
> paper-clip, for example. But I've never twisted a spoke that badly; it would take quite a few
> twists to get a 5-mm pattern!

The bands are concentric and not helical. Spoke twist may play a role but since the bands are
uniformly distributed on nearly all of the left spokes, I might doubt that. Your paper-clip analogy
is spot on. I don't know if the bands are due to torsion or tension but this is the same kind of
discoloration that you see on your twisted paper-clip.

I posted a couple pictures of the spokes at http://64.29.137.170 if you'd like to take a look. I'm
not very good with a digital camera (or any camera for that matter) but I think you'll be able to
see the effect I've tried to describe.

 

[Bbb]

[email protected] (BBB) wrote in message
news:<[email protected]>...

> I built a 7-speed rear wheel from straight 15 gauge spokes that I had on hand. After bringing the
> wheel to proper tension and true, I noticed that most of the spokes on the left side of the wheel
> had a periodic pattern of alternating dark and light bands along the spoke. Each band was about
> 5mm in length. I then looked much more closely at the spokes on the right side; I noticed that
> some of them had similar bands but they were very faint. The left spokes were manufactured by
> Wheelsmith and the right spokes by DT.
>
> The effect reminds me a little of "shear banding". Shear banding occurs when elastic materials are
> so stressed that they start to undergo plastic deformations. The spoke tensions in my wheel don't
> seem that high: tensions on the left are around 60kgf (egad, who IS responsible for that unit?)
> and on the right about 125kgf.

Just to close this thread, I think I know what caused the banding. I believe it has alot to do with
how the steel wire is processed. If the wire is drawn while hot, then surface tension will act to
deform the wire. This "capillary pinch instability" is the same kind of effect that causes liquid
jets to break up into droplets. The hot steel wire will be unstable to modes with wavelengths that
are longer that \pi times the diameter of the wire (a little over 5mm) and although the wire will
cool and solidify before it pinches off, small variations in the diameter of the wire will remain. I
believe that when the wire comes under tension, these variations become visible and appear as bands.

Both the DT and Wheelsmith 15 gauge spokes show this effect but the Wheelsmith spokes show it more.
The wire that is used to make DT spokes must come from a hot-drawn process that has more control
over this capillary effect...maybe the DT wire cools faster than the Wheelsmith wire.

I no longer think the banding will greatly affect the strength of my spokes. Time to ride.

 

[Dave Korzekwa]

[email protected] (BBB) writes:

>
> Just to close this thread, I think I know what caused the banding. I believe it has alot to do
> with how the steel wire is processed. If the wire is drawn while hot, then surface tension will
> act to deform the wire. This "capillary pinch instability" is the same kind of effect that causes
> liquid jets to break up into droplets. The hot steel wire will be unstable to modes with
> wavelengths that are longer that \pi times the diameter of the wire (a little over 5mm) and
> although the wire will cool and solidify before it pinches off, small variations in the diameter
> of the wire will remain. I believe that when the wire comes under tension, these variations become
> visible and appear as bands.

I am sure the spokes are cold drawn or swaged as the final step. However, you can get lubrication
instabilities in cold drawing, and swaged surfaces can also have funny looking variations in finish
like those in your pictures. Can you measure differences in the diameter between bands?

>
> Both the DT and Wheelsmith 15 gauge spokes show this effect but the Wheelsmith spokes show it
> more. The wire that is used to make DT spokes must come from a hot-drawn process that has more
> control over this capillary effect...maybe the DT wire cools faster than the Wheelsmith wire.
>
> I no longer think the banding will greatly affect the strength of my spokes. Time to ride.

I would agree here.

Dave Korzekwa

 

[Jobst Brandt]

Birk Brat who? writes:

> Both the DT and Wheelsmith 15 gauge spokes show this effect but the Wheelsmith spokes show it
> more. The wire that is used to make DT spokes must come from a hot-drawn process that has more
> control over this capillary effect...maybe the DT wire cools faster than the Wheelsmith wire.

I don't know how Wheelsmith spoke wire is produced but DT is cold drawn and is at maximum work
hardening. Further working does not increase its yield strength.

> I no longer think the banding will greatly affect the strength of my spokes.

If not "greatly" then how much?

> Time to ride.

Time not to lather us with your strength of materials posturing and asking whether the spokes are
safe to ride. I guess your question was just a ploy to expound on how much you know about it...
nothing, judging from the question.

Jobst Brandt [email protected] Palo Alto CA

 

[Bbb]

[email protected] wrote in message news:<[email protected]>...
> Birk Brat who? writes:
>
> > Both the DT and Wheelsmith 15 gauge spokes show this effect but the Wheelsmith spokes show it
> > more. The wire that is used to make DT spokes must come from a hot-drawn process that has more
> > control over this capillary effect...maybe the DT wire cools faster than the Wheelsmith wire.
>
> I don't know how Wheelsmith spoke wire is produced but DT is cold drawn and is at maximum work
> hardening. Further working does not increase its yield strength.
>
> > I no longer think the banding will greatly affect the strength of my spokes.
>
> If not "greatly" then how much?
>
> > Time to ride.
>
> Time not to lather us with your strength of materials posturing and asking whether the spokes are
> safe to ride. I guess your question was just a ploy to expound on how much you know about it...
> nothing, judging from the question.

Yeah. Not only do I not know anything about it the process of making spokes, I got it totally wrong.
When building the second wheel with the same spokes I could see the bands faintly before they were
tensioned. It's all in the finish.

 

[Mike Jacoubowsk]

> Yeah. Not only do I not know anything about it the process of making spokes, I got it totally
> wrong. When building the second wheel with the same spokes I could see the bands faintly before
> they were tensioned. It's all in the finish.

Don't feel bad. I've seen what you described many times, and never gave it a second thought, aside
from "That's an interesting appearance, looks kinda cool!" Yeah, I'd never make it as an engineer,
never got to the point of worrying that there could actually be something seriously wrong with the
spokes. I always assumed it was just an anomaly that occurred during the drawing process, and since
spokes almost never fail except at their ends, it just didn't seem like a big deal. Never saw any
spoke breakage on those wheels either.

--Mike-- Chain Reaction Bicycles http://www.ChainReactionBicycles.com

"BBB" <[email protected]> wrote in message
news:[email protected]...
> [email protected] wrote in message
news:<[email protected]>...
> > Birk Brat who? writes:
> >
> > > Both the DT and Wheelsmith 15 gauge spokes show this effect but the Wheelsmith spokes show it
> > > more. The wire that is used to make DT spokes must come from a hot-drawn process that has more
> > > control over this capillary effect...maybe the DT wire cools faster than the Wheelsmith wire.
> >
> > I don't know how Wheelsmith spoke wire is produced but DT is cold drawn and is at maximum work
> > hardening. Further working does not increase its yield strength.
> >
> > > I no longer think the banding will greatly affect the strength of my spokes.
> >
> > If not "greatly" then how much?
> >
> > > Time to ride.
> >
> > Time not to lather us with your strength of materials posturing and asking whether the spokes
> > are safe to ride. I guess your question was just a ploy to expound on how much you know about
> > it... nothing, judging from the question.
>
> Yeah. Not only do I not know anything about it the process of making spokes, I got it totally
> wrong. When building the second wheel with the same spokes I could see the bands faintly before
> they were tensioned. It's all in the finish.