The Basics of Wheel Alignment and Wheelbuilding

Weisse Luft wrote in message ...
These stainless steels are all austenitic, meaning they have no
ferromagnetic properties in their annealed state. Plastic deformation
changes this structure to partially ferritic structure making highly
cold worked stainless steels (with some exceptions like 316, a
molybdenum modification of 18-8) slightly magnetic. In addition, this
crystaline change greatly increases the yield strength and is HIGHLY
ansitropic in its effects.

Not that it is relevant but what is "ansitropic"
TJ

"jim beam" wrote

ah, this explains everything! stainless steel has been developed that
has an endurance limit! and it's used in bicycle spokes!!!

no. this is one of the fundamental flaws of "the book". it cites
material behavior for mild steel, which /does/ have an endurance limit,
and then presumes to describe behavior in stanless steel, which does
not. just exactly how this lends credibility to a revolutionary means
of eliminating metal fatigue is something i have yet to come to terms with.


http://www.hghouston.com/ss_cwp.html

"Weisse Luft" wrote

The overstressing procedure forces changes in the elbow, causing it to
conform to the flange hole AND causing deformation of the flange hole
itself. Because of this, the stresses of the bend is now spread over a
longer range of the bend. Cyclic loading consistent with riding is now
operating this joint in a purely elastic range rather than exposing
tiny areas of the bend to very high stresses over very small areas.

Practically speaking, whether momentary overloading increase spoke fatigue
life by reducing residual manufacturing stresses or by "bedding in" the
spoke/flange interface is immaterial, as long as it works, it's a procedure
that should be followed. For the "bedding" theory to be correct, it would
require that the bulk material in both the spoke and flange to be taken beyond
yield. I don't think that's the recommended practice. Your version of
"bedding", since it involves higher forces, would necessarily also perform the
reduction of residual stresses, so the claim that it works by that particular
mechanism would seem impossible to prove. In fact, those of us who don't
stress relieve to yield, yet observe improved spoke lifetimes, would seem to
have experiences which refute that theory.

dianne_1234 wrote:
On Sun, 01 Aug 2004 19:03:14 -0700, jim beam
wrote:


his "stress relief" theory on the other hand is entirely subjective,


Can you suggest some ways such a theory might be tested?

fogel pretty much says it all. what /i/ would do is just set up a
fatigue testing machine and start stretching.

other ways to detect residual stress include x-ray diffraction, but
obviously, that's much more of an industrial research/academic exercise
rather than something we can replicate "at home".

wrote:
On Sun, 01 Aug 2004 21:45:24 -0500, dianne_1234
wrote:


On Sun, 01 Aug 2004 19:03:14 -0700, jim beam
wrote:


his "stress relief" theory on the other hand is entirely subjective,

Can you suggest some ways such a theory might be tested?


Dear Dianne,

One way would be to take before and after pictures that
either do or do not show microscopic changes in a squeezed
spoke.

(My understanding of such matters is so feeble that I should
add that "microscopic" may need to be replaced by "x-ray
diffraction" or even more exciting technologies involving
terms like "lattice" and "crystal" and "scanning
microscope"--or possibly "bi-focals.")

Unfortunately, this requires more than just swiping a spoke
across the bar-code reader at the grocery store, so I've
stopped holding my breath while waiting for such evidence to
appear.

Another test would be to find an industry in which a very
similar process has been developed and tested. The obvious
place to look would be spoked motorcycle wheels, or even the
spoked wheels of obsolete British sports cars. There might
be a paper detailing testing of spoke stress-relief lurking
out there somewhere. (If none can be found, this is not
proof that the theory is wrong--spokes in other applications
might be so over-engineered that stress-relief is pointless,
or the wheels elsewhere might just be badly built.)

A practical test would involve taking several brands of
modern spokes and subjecting batches of them to some Rube
Goldberg machine that mimics the rapid reduction of
otherwise steady tension in a rolling bicycle wheel for
millions of cycles. If the stress-relieved batch outlasted
the unsqueezed batch, it would settle the matter.

Because the subject is of little interest outside
rec.bicycles.tech, expensive and serious testing beyond
anecdote is unlikely. Perhaps someone will find a peer
reviewed paper on spokes (as opposed to related but arguably
different matters), but I expect that it would have turned
up by now if such a study existed.

there's plenty of stuff out there on high tensile wire.


(Again, the absence of a study is not proof for or against
the theory--and the Wiedemer citation that I assume appears
in the 3rd edition of "The Bicycle Wheel" might be
specifically on spokes. I take comfort in the fact that I'm
apparently not the only member of rec.bicycles.tech too
cheap to buy the newer edition.)

A less expensive (and less conclusive) test would be to find
a large group of dedicated bicyclists unaware of the spoke
squeezing theory and find out how often their spokes break.
The only group that I can think of that might fit this
description would be the Keirin racers of Japan, but it
wouldn't surprise me if they've thoughtlessly heard of the
stress-relief theory and ruined themselves as a control
group.

In any case, we could only compare such a group to a very
small, self-selected group here on rec.bicycles.tech. A
double-blind study is hard to arrange when there's little
interest and the testing is expected to take a long time.

One test that occurred to me is to find out what the spoke
squeezing theory predicts will happen to unsqueezed spokes.
Obviously, unsqueezed spokes are supposed to fatigue and
fail sooner than apparently immortal squeezed spokes, but
how much sooner? That is, given 72 spokes on a pair of
wheels built as similarly as possible, except for the spoke
squeezing, how many will break in each set of wheels in ten,
twenty, fifty, or a hundred thousand miles of similar
riding?

I haven't seen any such predictions, but making them might
help put the debate in perspective. My impression is that
those who doubt the theory would predict no significant
difference in spoke failure rates.

I have no idea what kind of failure rates would be predicted
for unsqueezed spokes by spoke-squeezing proponents, but it
would be fascinating to see what kind of predictions would
be made and how they would be supported.

Time to see how my troop of monkeys is doing on duplicating
the First Folio.

Carl Fogel

Peter Cole Wrote:
"
Practically speaking, whether momentary overloading increase spoke
fatigue
life by reducing residual manufacturing stresses or by "bedding in"
the
spoke/flange interface is immaterial, as long as it works, it's a
procedure
that should be followed. For the "bedding" theory to be correct, it
would
require that the bulk material in both the spoke and flange to be taken
beyond
yield. I don't think that's the recommended practice. Your version of
"bedding", since it involves higher forces, would necessarily also
perform the
reduction of residual stresses, so the claim that it works by that
particular
mechanism would seem impossible to prove. In fact, those of us who
don't
stress relieve to yield, yet observe improved spoke lifetimes, would
seem to
have experiences which refute that theory.

Yielding occurs only in a partial cross section of the spoke during the
stress relieving process. Because the entire cross section does not go
to yield, the tension can and does remain the same.

Anisotropic means properties that differ with respect to axis. A very
common anisotropic material would be wood.

With regard to cyclic fatigue, one has to only look at the spring
industry to see what works. For long life, most springs are entirely
cold worked, that is no post forming heat treatment is used. That cold
working is the same as the final stress relieving process some of us
follow when wheel building.

Now on compression, tension, aluminum and stainless. Its true aluminum
is best in compression while spokes can only take a tensile load but in
a wheel, we have a pretensioned structure. That spoke takes a
compressive load, manifested as a decrease in tension. And the wheel
is under a compressive load from the sum of the sopke tensions but it
also can take a tensile load, manifested by a reduction in the
compressive stress.


--
Weisse Luft

Trevor Jeffrey wrote:
Weisse Luft wrote in message ...

These stainless steels are all austenitic, meaning they have no
ferromagnetic properties in their annealed state. Plastic deformation
changes this structure to partially ferritic structure making highly
cold worked stainless steels (with some exceptions like 316, a
molybdenum modification of 18-8) slightly magnetic. In addition, this
crystaline change greatly increases the yield strength and is HIGHLY
ansitropic in its effects.


Not that it is relevant but what is "ansitropic"
TJ


"directional" is a simple translation. wood is anisotropic. metals get
like this when their grains are all elongated in the same direction,
wire being the classic example.

Wrote:
On Mon, 2 Aug 2004 13:58:26 +1000, You agree with the spoke-squeezing
side of the debate that
overstressing significantly increases spoke life, but you
believe that it has nothing to do with internal stress
relief and is instead a matter of a better mechanical mating
of the spoke elbow with the hub hole that spreads the load
out and greatly reduces the stress?

If so, would magnified before and after pictures of the hub
hole show a difference?

I have a vague notion that you've mentioned scuba equipment
in passing. Is that what you have in mind when you speak of
pressure vessels? I'm hoping to wander off into "auto
frettage," but can't figure out how it resembles the spoke
hole and elbow situation.

Thanks,

Carl Fogel

Yes, you can easily see the deformation from the spokes with only
slight magnification.

On pressure vessels, I was not covering any compressed gas bottle but
rather lower pressure vessels fabricated by welding and used for
storing materials like LPG and the like. Some are actually formed by
pressure.


--
Weisse Luft

Peter Cole wrote in message 5PqPc.195614$a24.110765@attbi_s03...

Practically speaking, whether momentary overloading increase spoke fatigue
life by reducing residual manufacturing stresses or by "bedding in" the
spoke/flange interface is immaterial, as long as it works, it's a procedure
that should be followed.

I do not believe that all constructors using the method of
overtensioning spokes have had an equal benefit. As I have said previously,
overtensioning, accidentally, partially forms the bend in the spoke at the
crossing point so as to reduce the angular displacement at the hub during
the cyclic variation of loading. With a reduced angular displacement at the
hub interface the MTBF is increased due to the lowered rate of fatigue. The
fatigue rate is primarily dependant upon the angular displacement and not
the tensile force or variation in thereof.
Relatively the momentary overloading is a waste of time compared to
specifically shaping the spoke correctly.
TJ

Mark McMaster wrote:
jim beam wrote:

Mark McMaster wrote:

jim beam wrote:

wrote:


snip

Spoke-squeezing is an intriguingly mysterious subject to
research. I remain agnostic, wavering one way and the other,
but haven't seen any experimental data or analyses involving
bicycle spokes. If you have the 3rd edition, perhaps you
could peek at the Wiedemer stuff and give me your thoughts
on it?





you may also want to consider this question:

q: elevator safety certification requires loading the cab to double
it's "safe working load". this is to test the wire ropes that
suspend it. the reason is that fracture mechanics predict that this
process will typically reveal by failure any latent flaws. but, if
we extend spoke squeezing theory, wouldn't this overload procedure
also prevent fatigue of elevator cables?

a: no. elevator cables still fatigue and need regular testing,
inspection & replacement.




This proves nothing one way or the other about the affects of
squeezing spokes to reduce residual stress. There is no question
that reducing residual (tensile) stresses can increase fatigue life.
There is also no question that spokes (or elevator cables) will still
fatigue if the cyclic load is high enough (i.e. above the endurance
limit). The question is whether squeezing the spokes provides any
significant beneficial reduction in residual stress, or increases the
endurance limit.

Mark McMaster



ah, this explains everything! stainless steel has been developed that
has an endurance limit! and it's used in bicycle spokes!!!

no. this is one of the fundamental flaws of "the book". it cites
material behavior for mild steel, which /does/ have an endurance
limit, and then presumes to describe behavior in stanless steel, which
does not. just exactly how this lends credibility to a revolutionary
means of eliminating metal fatigue is something i have yet to come to
terms with.


Ah, as usual, you dodge the question rather than addressing it. Whether
or not a material has a true endurance limit or not doesn't change the
question of whether momentarily overloading the spokes can reduce
residual stress and/or increase fatigue life, which is central to the
argument. But then, you appear to be far more interested in being a
contrarian than to actually knowing what is going on.

That momentarily overloading the spokes results in increased spoke life
has been reported by many sources. Not just here in the RBT newsgroup
but by others as well, both inside and outside the industry. For
example, here is the Bontrager wheel manual which shows how their "wheel
stressor" is used to momentarily overload the spokes:

http://www.bontrager.com/workshop/do...eel_manual.pdf

So, just what is the mechanism that causes the spokes to have
improved fatigue life after momentarily overloading them? If you
do not believe that Brandt is correct about relieving residual
stresses in the spokes, than what other explanation do you propose?

And about stainless steel having an endurance limit: Whether any
material has a true and absolute endurance limit is often debated.
However, under a common usage of the term (fatigue strength at 10^7
cycles is a common definition), the types of stainless steel used in
spokes does have an endurance limit (but then, you probably knew that).
We can dispose of that red herring.

Here are some data on some stainless steels of the type used in spokes
(for example, Wheelsmith uses 304, DT uses 18-8), including their
endurance limits:

http://www.hghouston.com/ss_cwp.html
http://www.band-it-idex.com/pdfs/sta...el/302_305.pdf
http://www.askzn.co.za/tech/tech_grade_304.htm


Mark McMaster



gotta scram for work so let's chat later, but be careful when talking
about endurance limits - they're easily confused with fatigue limits,
which may sound the same but are techically very different.