spoke breakage at nipple side

wrote:
It still seems to me that a kink in the spoke at the point where the
nipple and spoke meet would be the point where cyclical fatigue
would eventually result in failure if the spoke was flexed once per
revolution.

I don't understand why you think that. Unsupported bends cause
failure but not supported kinks in the spoke. Without that kink, the
spoke was bending near the end of the threads with every wheel
revolution. With the kink, spokes just pull from the spoke nipple
rather than around a bend at an angle to the last support point.

I hadn't thought of the bend at the nipple as being supported- I was
thinking of it as cycling between supported and unsupported as the
spoke was wound up with each revolution of the wheel. I can see how a
bend there supported by the edge of the nipple, with sufficient tension
so that the bend is always supported, could work as you suggest. I can
also see how alloy nipples could be problematic in this situation
because they could deform and cause the bend to become unsupported. Are
you sure that tension can be high enough on the non-drive side to
always provide sufficient support to the bend? Or maybe this is an
indication that tension was not high enough.

I thought I might have laced them to the wrong hole as it's really hard
to tell which side of the asymmetrical rim the holes are on. It
certainly appears I have the holes in the rim which are slightly to the
right going to the left side of the hub, but it's really hard to say.
The nipples are slightly larger than the spoke, so the spokes going to
the right hand side are centered on the nipple. The nipples used for
the non-drive side are touching the left-hand side of the spokes.
There are breaking at that stress point.

Does anybody have this rim? If so, put the valve stem hole at the
bottom and tell me where does the first spoke towards the front of the
bike next to the valve stem go: to the cogset side or to the non-drive
side?

anonymous writes:

It still seems to me that a kink in the spoke at the point where
the nipple and spoke meet would be the point where cyclical
fatigue would eventually result in failure if the spoke was flexed
once per revolution.

I don't understand why you think that. Unsupported bends cause
failure but not supported kinks in the spoke. Without that kink,
the spoke was bending near the end of the threads with every wheel
revolution. With the kink, spokes just pull from the spoke nipple
rather than around a bend at an angle to the last support point.

I hadn't thought of the bend at the nipple as being supported- I was
thinking of it as cycling between supported and unsupported as the
spoke was wound up with each revolution of the wheel. I can see how
a bend there supported by the edge of the nipple, with sufficient
tension so that the bend is always supported, could work as you
suggest. I can also see how alloy nipples could be problematic in
this situation because they could deform and cause the bend to
become unsupported. Are you sure that tension can be high enough on
the non-drive side to always provide sufficient support to the bend?
Or maybe this is an indication that tension was not high enough.

If the spoke is bent as described in "the Bicycle Wheel" with
tensioned spokes, the bend, by definition, is resting against the
spoke nipple. Even if the spoke were to go slack intermittently, its
shape would always pull from the edge of the spoke nipple. With
aluminum spoke nipples, stress relieving would assure that spokes were
supported by the lip of the spoke nipple... assuming the spoke were
suitably bent. I think the pictures show that aspect.

Jobst Brandt

wrote:
I've got some 14/15/14 double butted spokes laced to a chorus rear hub
and a Ritchey Aero OCR rim. I've broken two spokes since building the
wheel (about 2 thousand miles) and I've looked into it. It seems that
the spoke nipples are perpendicular to the rim, while the spokes enter
the rim at an angle (obviously). The end of the spoke nipple is
touching the outside of the spoke and the two spokes have broken where
the tread stops. The non-drive side are the ones breaking.

I'm pretty sure I have the spokes going to the proper hole in the rim
as the drive side looks fine. The spokes entering from the non-drive
side that are crossing on the outside have a distinct angle change
between the spoke and the nipple.

Why?

Should I remove the 8 spokes that are outside-crossing on the non-drive
side and drill the rim such that the nipple will be able to angle
towards the spokes?

Anything else I might be doing wrong?

imo, incorrect rim orientation is the most likely cause - from what i've
seen of these rims, they are drilled to orient spoke nipples to optimum,
so if yours are not, you're one spoke hole out.

as for bending spokes, it doesn't really address the issue. if you have
a bend, every time you increase or decrease tension. as you will in any
loading with use situation, you flex the bend, regardless of whether
that be visible or not. and any cyclic flex is still subject to
fatigue. get rim hole orientation right first, using a drill to
"assist" hole orientation if necessary. you should be fine after that.
try a diffeent brand of nipple if necessary. sapim are marginally
skinnier for example, and this will help. you don't mention brand of
spoke - fatigue life is primarily a function of spoke quality.

avoid excessive "stress relief". residual stress [such as it may be] is
compressive at the thread roots, so "relief" sufficient to yield these
thread roots will make fatigue worse, not better.

wrote:
I thought I might have laced them to the wrong hole as it's really hard
to tell which side of the asymmetrical rim the holes are on. It
certainly appears I have the holes in the rim which are slightly to the
right going to the left side of the hub, but it's really hard to say.
The nipples are slightly larger than the spoke, so the spokes going to
the right hand side are centered on the nipple. The nipples used for
the non-drive side are touching the left-hand side of the spokes.
There are breaking at that stress point.

Does anybody have this rim? If so, put the valve stem hole at the
bottom and tell me where does the first spoke towards the front of the
bike next to the valve stem go: to the cogset side or to the non-drive
side?

Cogset side.