Pedal-crank interface, fretting, and gouging.

Post by Michael Press
I have read about how a pedal will make a gouge in the crank face
as it precesses in the crank threads. I have a new TA crank set
and Shimano pedals. The pedal has a flange between the pedal
spindle and the pedal threads. The flange fits exactly inside a
space in the crank face when the pedal is threaded into the crank.
Will this flanged reduce gouging of the crank face by the pedal?
ASCII art follows. Thanks.
_________________
| |
| |
| |
| crank body |
| --
| | | <-- flange
| | |
|/\/\/\/\/\/\/\| |_________________
|
| pedal threads pedal spindle --->
|
|/\/\/\/\/\/\/\ _________________
| | |
| | |
| --
| crank body |
| |
| bottom bracket |
| || |
| \/ |
| |
| |

no, it cannot. all the recess does is offset it from the surface, but
that doesn't make any difference to whether fretting will occur - it
still happens under the spindle interface, regardless of where that
interface is located.

if you're worried about fatigue, the recess will make little difference.
fatigue usually initiates at surface stress risers, where the riser is
perpendicular to the stress. in the case of any damaged created by
fretting, at first glance, it may be possible to suppose that fretting
has initiated cracking, but closer inspection reveals that the fatigue
cracks never initiate perpendicular to the riser, hence this supposition
is misplaced. modern cranks rarely fail thanks to better materials, yet
the mechanical interface remains unchanged.

Luns Tee

2005-05-17 00:14:55 UTC

Post by jim beam
fatigue usually initiates at surface stress risers, where the riser is
perpendicular to the stress. in the case of any damaged created by
fretting, at first glance, it may be possible to suppose that fretting
has initiated cracking, but closer inspection reveals that the fatigue
cracks never initiate perpendicular to the riser, hence this supposition
is misplaced.

Your arguments of crack direction are misplaced. Notice that
fatigue cracks through metals leave a rough surface and not a smooth
glassy one. This is because the cracks follow grain boundaries of the
metal, with the direction of the applied stress only roughly guiding the
crack propogation. A 90 degree change in direction as a crack follows
its way around grain boundaries is nothing - these happen all over the
surface of any fatigue failure.

Post by jim beam
modern cranks rarely fail thanks to better materials, yet
the mechanical interface remains unchanged.

You keep on saying this, offering no evidence, all the while
accusing Jobst of giving unsubstantiated arguments. Quit it with this
hypocrisy and put your cards on the table. What evidence do you have
that materials have changed at all? What alloys were used before that
would fail, and what alloys are so much better today that they don't?
Even if failures are less common with newer cranks as you claim, that
observation - the only one I've seen you offer - on its own tells
nothing about what materials are being used.

-Luns

jim beam

2005-05-17 03:40:05 UTC

no, luns, fatigue cracking is transgranular, not intrgranular. the
crack surface has two main regions, that with "beach marks" [created by
the cyclical "blunting" process] and fast fracture. neither are
intergranular processes in stage 1, and rarely in stage 2, at least, not
in aluminum. even steels need to be below their brittle transition
temperature for the fast fracture phase to be intergranular. now, some
/other/ cracks can be intergranular, such as stress corrosion &
corrosion fatigue, but these are somewhat different regimes from that
seen in an aluminum crank arm.

as for cracking initiating at grain boundries, you're going to have a
hard time proving that one in the presence of any slip plane activation,
inclusion content or mechanical features in the surface of the component.

Post by jim beam
modern cranks rarely fail thanks to better materials, yet
the mechanical interface remains unchanged.

You keep on saying this, offering no evidence, all the while
accusing Jobst of giving unsubstantiated arguments.

well, substantiation that crank arms fail due to fretting was supposed
back when pedal eyes frequently /did/ break, [despite the obvious
problem with fretting damage not being oriented for that to happen] but
since the late 80's & 90's, pedal eye failures have stopped. why?
pedal eye designs haven't changed much. pedals /definitely/ haven't
changed. so why can't i find pictured of failed modern era pedal eyes
all over the net? sorry luns, the evidence is everywhere - /lack/ of
failure.

Post by Luns Tee
Quit it with this
hypocrisy and put your cards on the table. What evidence do you have
that materials have changed at all? What alloys were used before that
would fail, and what alloys are so much better today that they don't?
Even if failures are less common with newer cranks as you claim, that
observation - the only one I've seen you offer - on its own tells
nothing about what materials are being used.

the difference is that modern alloys have much lower inclusion counts
today than before. look into vacuum metallurgy & zone refining. mass
adoption of these processes have reduced cost to levels viable for bike
component manufacture.

Post by Luns Tee
-Luns

Jose Rizal

2005-05-17 13:35:03 UTC

Post by jim beam
as for cracking initiating at grain boundries, you're going to have a
hard time proving that one in the presence of any slip plane activation,
inclusion content or mechanical features in the surface of the component.

What an impressive display of technobabble. Why don't YOU prove that
there is in fact "slip plane activation" in the specific alloy involved
in the specific pedal component, that there is any effect of "inclusion
content" or "mechanical features" (whatever this means)? And no,
looking up these terms in textbooks isn't proof of your theory; the
existence of these terms does not support your application of these in
your theories.

modern cranks rarely fail thanks to better materials, yet the
mechanical interface remains unchanged.

You keep on saying this, offering no evidence, all the while
accusing Jobst of giving unsubstantiated arguments.

Unless you have access to rates of failures from manufacturers, or you
have done a comprehensive survey of failures (looking for pictures on
the internet doesn't cut it, I'm afraid), you're just blowing hot air.

Post by jim beam
why? pedal
eye designs haven't changed much. pedals /definitely/ haven't changed.
so why can't i find pictured of failed modern era pedal eyes all over
the net? sorry luns, the evidence is everywhere - /lack/ of failure.

Your failure to find pictures of these sorts of failures on the internet
is by no means "evidence is everywhere" of non-existence of these
failures. Your search methodology is flawed, and does not constitute a
credible scientific survey. The best place to look for failures of this
sort will be the manufacturers; they will, after all, have the warranty
claims. Now ask yourself how likely it is that these manufacturers will
show pictures of pedal failures on the net.

the difference is that modern alloys have much lower inclusion counts
today than before.

In other words, you're guessing. Just because you say so does not mean
it is so. State the examples and include specifics.

Post by jim beam
look into vacuum metallurgy & zone refining. mass
adoption of these processes have reduced cost to levels viable for bike
component manufacture.

In other words, you're guessing again. Specifics, specifics.....

Sandy

2005-05-17 14:40:35 UTC

Post by Jose Rizal
Unless you have access to rates of failures from manufacturers, or you
have done a comprehensive survey of failures (looking for pictures on
the internet doesn't cut it, I'm afraid), you're just blowing hot air.

A small caveat : I think you may well find that the rate of failure is not
capable of meaningful calculation. Unless, you include all units made, and
don't discriminate between those which are barely used in any term, and
those which are used, abused, misinstalled, etc. The low (likely) rate of
failure will not inform ; nor will the emotional anecdotal histories.

As with all human designed and made stuff, there will be a limit of how
little failure to reach for, while assuring a relatively low investment in
that goal. Some companies may well be happy with exceptionally generous
warranty policies (muting lots of criticism - balancing for marginal
products), and other companies will market their devotion to scrupulous
detailed engineering advancement and quality assurance in manufacture. I
don't think that typically profitable enterprises side with the latter, and
ones that prefer the former approach may find a stressful balance in
achieving customer satisfaction.

So, Mr Brandt, Mr beam, it's likely that you are both right and both wrong,
and not dividend-receiving shareholders of either such enterprises.

--
Bonne route,

Sandy
Verneuil-sur-Seine FR

jim beam

2005-05-18 12:58:57 UTC

Post by Jose Rizal

Post by jim beam
as for cracking initiating at grain boundries, you're going to have a
hard time proving that one in the presence of any slip plane
activation, inclusion content or mechanical features in the surface of
the component.

jose, with respect, all these terms /are/ abundant in the literature -
they are the means by which fatigue initiates. if you are unfamiliar
with them, or can't be bothered to look them up on google, i'm not the
guy to educate you to. if you think their use inappropriate for a
"tech" newsgroup, perhaps you are in the wrong place.

Post by Jose Rizal
And no,
looking up these terms in textbooks isn't proof of your theory; the
existence of these terms does not support your application of these in
your theories.

modern cranks rarely fail thanks to better materials, yet the
mechanical interface remains unchanged.

You keep on saying this, offering no evidence, all the while
accusing Jobst of giving unsubstantiated arguments.

Post by jim beam
why? pedal eye designs haven't changed much. pedals /definitely/
haven't changed. so why can't i find pictured of failed modern era
pedal eyes all over the net? sorry luns, the evidence is everywhere -
/lack/ of failure.

the difference is that modern alloys have much lower inclusion counts
today than before.

In other words, you're guessing. Just because you say so does not mean
it is so. State the examples and include specifics.

Post by jim beam
look into vacuum metallurgy & zone refining. mass adoption of these
processes have reduced cost to levels viable for bike component
manufacture.

In other words, you're guessing again. Specifics, specifics.....

Jose Rizal

2005-05-19 04:25:25 UTC

Post by Jose Rizal

Post by jim beam
as for cracking initiating at grain boundries, you're going to have a
hard time proving that one in the presence of any slip plane
activation, inclusion content or mechanical features in the surface
of the component.

jose, with respect, all these terms /are/ abundant in the literature -
they are the means by which fatigue initiates.

There you go again, sidestepping the issue. The fact that these terms
are "abundant" in the literature does not support your case in any way.
Yet you bandy these words about as if the mention of the terms proves
your case, when in fact you have absolutely no quantifying arguments for
your theories.

Post by jim beam
if you are unfamiliar
with them, or can't be bothered to look them up on google, i'm not the
guy to educate you to.

Sidestep number two: there was no indication whatsoever that I am
unfamiliar with these terms. In fact, it's because I know these terms
that I call you on your technobabble smokescreen.

Post by jim beam
if you think their use inappropriate for a
"tech" newsgroup, perhaps you are in the wrong place.

Sidestep number three: what an irrelevant strawman argument... you do
know that you're not fooling many people, don't you?

And oh look, no response whatsoever to the real issues and challenges
you've been thrown below... why is that so unsurprising?

Post by Jose Rizal
And no, looking up these terms in textbooks isn't proof of your
theory; the existence of these terms does not support your application
of these in your theories.

modern cranks rarely fail thanks to better materials, yet the
mechanical interface remains unchanged.

You keep on saying this, offering no evidence, all the while
accusing Jobst of giving unsubstantiated arguments.

Post by jim beam
why? pedal eye designs haven't changed much. pedals /definitely/
haven't changed. so why can't i find pictured of failed modern era
pedal eyes all over the net? sorry luns, the evidence is everywhere
- /lack/ of failure.

Your failure to find pictures of these sorts of failures on the
internet is by no means "evidence is everywhere" of non-existence of
these failures. Your search methodology is flawed, and does not
constitute a credible scientific survey. The best place to look for
failures of this sort will be the manufacturers; they will, after all,
have the warranty claims. Now ask yourself how likely it is that
these manufacturers will show pictures of pedal failures on the net.

the difference is that modern alloys have much lower inclusion counts
today than before.

In other words, you're guessing. Just because you say so does not
mean it is so. State the examples and include specifics.

Post by jim beam
look into vacuum metallurgy & zone refining. mass adoption of these
processes have reduced cost to levels viable for bike component
manufacture.

In other words, you're guessing again. Specifics, specifics.....

c***@comcast.net

2005-05-14 05:44:18 UTC

On Sat, 14 May 2005 03:39:02 GMT, Michael Press

Dear Michael,

Is the edge of the flange squared at right angles like this:

|/\/\/\/\/\/\/\ _________________
| | |
| | |
| --

Or tapered more like a car-wheel for a lug-nut:

|/\/\/\/\/\/\/\ _________________
| \ |
| \ |
| \|

I'm only trying to clarify what other posters may debate.

Carl Fogel

Zog The Undeniable

2005-05-14 07:03:11 UTC

It's just a thin flat washer, which TA always use on their cranksets.
It may spread the load a little but doesn't fully solve the problem of
the pedal eating the crank.

Michael Press

2005-05-14 07:41:09 UTC

Post by c***@comcast.net
On Sat, 14 May 2005 03:39:02 GMT, Michael Press

Dear Michael,
|/\/\/\/\/\/\/\ _________________
| | |
| | |
| --

Squared.

...

Post by c***@comcast.net
Carl Fogel

--
Michael Press

j***@stanfordalumni.org

2005-05-14 17:07:29 UTC

So it won't show a gouge in the aluminum crank but it will move,
either at the washer to pedal spindle interface or between the washer
and crank. That motion will have a crack generating effect on the
most highly loaded threads near the washer and can generate cracks
just the same. This feature only hides the effect. It's a Bandaid(R).

Just the same, I find interesting that TA recognized the presence of a
problem without analyzing effect it has and how to fix it. Discussing
this with crank/pedal manufacturers is a tricky subject. I am amazed
at all the slippery dodges they can muster in defense of current
practice.

***@stanfordalumni.org

jim beam

2005-05-14 18:05:27 UTC

really? when's the last time you saw a modern dura-ace or record pedal
eye failure? same interface as ever before. and how exactly do these
cracks get generated? they're not perpendicular to the stress risers
generated by fretting.

Post by j***@stanfordalumni.org
Just the same, I find interesting that TA recognized the presence of a
problem without analyzing effect it has and how to fix it. Discussing
this with crank/pedal manufacturers is a tricky subject. I am amazed
at all the slippery dodges they can muster in defense of current
practice.

there's no slippery dodge. pedal eye's don't fail any more due to use
of better materials. if they're not failing, there's nothing to fix.

Michael Press

2005-05-15 05:04:08 UTC

So it won't show a gouge in the aluminum crank but it will move,
either at the washer to pedal spindle interface or between the washer
and crank. That motion will have a crack generating effect on the
most highly loaded threads near the washer and can generate cracks
just the same. This feature only hides the effect. It's a Bandaid(R).
Just the same, I find interesting that TA recognized the presence of a
problem without analyzing effect it has and how to fix it. Discussing
this with crank/pedal manufacturers is a tricky subject. I am amazed
at all the slippery dodges they can muster in defense of current
practice.

Thank you. I anticipated the general direction of your analysis.
There is no "washer to pedal spindle interace" as you wrote. What
you are calling a "washer" is in fact a flange on the pedal
spindle/threaded-bolt element; they are all one piece of steel.
The flange sits inside a counter sunk area on the crank face. Is
this how you see the diagram?

--
Michael Press

Luns Tee

2005-05-15 08:28:52 UTC

Post by Michael Press
Thank you. I anticipated the general direction of your analysis.
There is no "washer to pedal spindle interace" as you wrote. What
you are calling a "washer" is in fact a flange on the pedal
spindle/threaded-bolt element; they are all one piece of steel.
The flange sits inside a counter sunk area on the crank face. Is
this how you see the diagram?

While you may not have them, TA does (did?) make and sell pedal
washers, and I believe the recess in the cranks is put there with the
intent that you use their washers in the recess.

How deep is the recess in your cranks? If I'm not mistaken, TA
pedal washers are about a quarter of a mm thick.

-Luns

Zog The Undeniable

2005-05-15 17:41:41 UTC

Post by Luns Tee
While you may not have them, TA does (did?) make and sell pedal
washers, and I believe the recess in the cranks is put there with the
intent that you use their washers in the recess.
How deep is the recess in your cranks? If I'm not mistaken, TA
pedal washers are about a quarter of a mm thick.

Yes, the Alize range still uses them. They're supplied with new cranks.

Phil, Squid-in-Training

2005-05-16 04:40:26 UTC

In article

While you may not have them, TA does (did?) make and sell pedal
washers, and I believe the recess in the cranks is put there with the
intent that you use their washers in the recess.
How deep is the recess in your cranks? If I'm not mistaken, TA
pedal washers are about a quarter of a mm thick.

The pedal washers on my mountain bike cranks are at least 1mm thick. Think
it makes more of a difference?

--
Phil, Squid-in-Training

d***@yahoo.com

2005-05-16 15:09:01 UTC

i'm confused. if the pedal shaft is coated with re loctite , no
movement no excessive pressure will occur?
but i'm ignorant-are both shaft and crank aluminum?

A Muzi

2005-05-18 05:51:39 UTC

Post by d***@yahoo.com
i'm confused. if the pedal shaft is coated with re loctite , no
movement no excessive pressure will occur?
but i'm ignorant-are both shaft and crank aluminum?

The forces involved are beyond loctite's bond.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

c***@comcast.net

2005-05-18 07:14:18 UTC

On Wed, 18 May 2005 00:51:39 -0500, A Muzi

Post by A Muzi

Post by d***@yahoo.com
i'm confused. if the pedal shaft is coated with re loctite , no
movement no excessive pressure will occur?
but i'm ignorant-are both shaft and crank aluminum?

The forces involved are beyond loctite's bond.

Dear Andrew,

The forces are beyond even the grip of duct tape.

But a paste made from the wompom would work:

Now the thick inner shell of a Wompom
You can mould with a finger and thumb.
Though soft when you began it
It'll set as hard as granite
And it's quite as light as aluminium.

The full materials description follows.

Carl Fogel

You can do such a lot with a Wompom,
You can use every part of it too.
For work or for pleasure,
It's a triumph, it's a treasure,
Oh there's nothing that a Wompom cannot do.

Now the thread from the coat of the Wompom
Has the warmth and resilience of Wool
You need never wash or brush it,
It's impossible to crush it
And it shimmers like the finest sort of tulle.

So our clothes are all made from the Wompom;
Modern Gowns, Sportswear, Lingerie (Going up)
They are waterproof and plastic
Where it's needed they're elastic
And they emphasise the figure as you see.

Hail, to thee blithe Wompom.
Hail, to thee O Plant!
All-providing Wompom.
Universal Aunt!

You can shave with the rind of a Wompom,
And it acts like a soapless shampoo.
And its root in little doses
Keeps you free from halitosis
Oh, there's nothing that a Wompom cannot do,
Nothing that a Wompom cannot do,
Nothing that a Wompom cannot do.

Now the thick inner shell of a Wompom
You can mould with a finger and thumb.
Though soft when you began it
It'll set as hard as granite
And it's quite as light as aluminium.

So we make what we like from the Wompom,
And that proves very useful indeed.
From streets full of houses
To the buttons on your trousers
With a Wompom you have everything you need.

Gaudeamus Wompom,
Gladly we salute!
Vade mecum Wompom,
Philanthropic Fruit!

Oh, the thin outer leaf of the Wompom
Makes the finest Havana cigar
And its bottom simply bristles
With unusual looking thistles
But we haven't yet discovered what they are.

You can do such a lot with a Wompom,
You can use every part of it too.
For work or for pleasure,
It's a triumph, it's a treasure,
Oh there's nothing that a Wompom cannot do.

Oh, the flesh in the heart of a Wompom
Has the flavour of porterhouse steak.
And its juice is a liquor
That will get you higher quicker
And you're still lit up next morning when you wake.

Wompom! Wompom!
Let your voices ring!
Wompom! Wompom!
Evermore we sing!

To record what is what in a Wompom
Needs a book twice as thick as Who's Who
I could tell you more and more about this fascinating flora
You can shape it, you can square it,
You can drape it you can wear it,
You can ice it, You can dice it,
You can pare it, You can slice it,
Oh there's nothing that a Wompom cannot do!
Nothing that a Wompom cannot do!
Nothing that a Wompom cannot do!

f***@yahoo.com

2005-05-18 15:10:35 UTC

Post by A Muzi

Post by d***@yahoo.com
i'm confused. if the pedal shaft is coated with re loctite , no
movement no excessive pressure will occur?
but i'm ignorant-are both shaft and crank aluminum?

The pedal shaft is not aluminum. Usually it's steel.

Post by A Muzi
The forces involved are beyond loctite's bond.

Loctite is more than "bond." That is, it's anti-loosening properties
work differently than, say, putting Super Glue on the threads.

Loctite acts as a gap filler. In tight metallic spaces (assuming the
right types of metals) it turns to hard plastic. When it does this, it
fills the slight clearance space between a male and female thread.
This filling is beneficial in preventing loosening of threads.

Here's why: If a nut and bolt had frictionless thread, you could
loosely screw the nut onto the bolt, then grab the bolt head and let
the bolt hang vertically. The mere weight of the nut would cause it to
spin right off, sliding down the thread's helical ramp. If instead of
the nut's weight, you had a larger tensile load on the assembly, the
same thing would happen. Good thing threads have friction, right?

But threads generally have to have clearance space to allow easy
installation. So if you took a real nut and bolt and screwed them
loosely together, then hung things vertically, you can shift the nut
radially (side to side) on the bolt a few thousandths of an inch.

If you did this carefully enough, each time you shifted the nut
sideways on the bolt, it would slide down the thread ramp a little bit,
despite the friction.

You can see this on a bigger scale by making a ramp on your desk (prop
up one end of a book) and putting some small object on the ramp (maybe
an eraser). Apply force on the eraser sideways; it moves sideways, but
it also moves down the ramp a bit, despite the friction.

So a sideways relative motion of a mating thread causes some tiny loss
in bolt tension. Do it often enough - as on an old Harley Davidson -
and the tension is gone, the nut is loose, and parts are left behind on
the highway.

Hardened Loctite takes up space to prevent that side-to-side motion. I
think this action is at least as important as its adhesive action.

Now I don't know the relationship between the bond strength and the
compressive strength of hardened Loctite. If I were to try Loctite
thread locker on pedals, I'd use the purple (weakest) stuff. Maybe
it's too soft to prevent the motion in that laterally loaded
pedal-crank joint. But I'd guess it would prevent almost all of the
motion.

There are other problems with this idea, though. Not all metals
trigger the solidification of Loctite. In particular, aluminum and
plated steel aren't the greatest. See
http://www.loctite.com/int_henkel/loctite_us/index.cfm?&pageid=214&layout=2
about halfway down.

- Frank Krygowski

j***@stanfordalumni.org

2005-05-16 18:36:29 UTC

Post by Phil, Squid-in-Training

Post by Michael Press
Thank you. I anticipated the general direction of your analysis.
There is no "washer to pedal spindle interface" as you wrote.
What you are calling a "washer" is in fact a flange on the pedal
spindle/threaded-bolt element; they are all one piece of steel.
The flange sits inside a counter sunk area on the crank face. Is
this how you see the diagram?

While you may not have them, TA does (did?) make and sell pedal
washers, and I believe the recess in the cranks is put there with
the intent that you use their washers in the recess.
How deep is the recess in your cranks? If I'm not mistaken, TA
pedal washers are about a quarter of a mm thick.

The pedal washers on my mountain bike cranks are at least 1mm thick.
Think it makes more of a difference?

At 1mm thickness the washer is merely a shim of insignificant bending
strength, considering the forces exerted by a canting pedal spindle.
Don't assume that because TA makes cranks that they understand the
stresses encountered in use. This has not been the case in much of
the bicycle industry. For that you can consider the Shimano Octalink
drive, the Campagnolo aluminum freewheel or their Delta brake only as
prime examples. The ISIS spindle failures at the sharp discontinuity
at the end of the spline is another.

You are the failure analysis laboratory in many instances.
Unfortunately, many failure observers assume it must have been their
fault because the manufacturer would not have put the item on the
market had it not been found to be reliable.

The reason this persists is that few skilled engineers are involved in
the products or the legal pursuit of failures. The bicycle industry
is a stepchild in that respect and in the USA, where such things could
be corrected, the public at large believes bicycling is a dangerous
game, not to be taken seriously. "They deserve what they get."

***@stanfordalumni.org

Matt O'Toole

2005-05-16 20:53:38 UTC

Post by j***@stanfordalumni.org
You are the failure analysis laboratory in many instances.
Unfortunately, many failure observers assume it must have been their
fault because the manufacturer would not have put the item on the
market had it not been found to be reliable.
The reason this persists is that few skilled engineers are involved in
the products or the legal pursuit of failures. The bicycle industry
is a stepchild in that respect and in the USA, where such things could
be corrected, the public at large believes bicycling is a dangerous
game, not to be taken seriously. "They deserve what they get."

Don't forget the wannbe racer marketing which fosters an attitude that high
performance equipment must be finicky and unreliable. The more finicky and
unreliable it is, the more specialty cachet it has.

Matt O.

d***@yahoo.com

2005-05-16 21:12:56 UTC

holy cow!

Bill Sornson

2005-05-16 23:58:33 UTC

Post by d***@yahoo.com
holy cow!

serenity now!

j***@stanfordalumni.org

2005-05-15 13:43:21 UTC

Post by Michael Press

So it won't show a gouge in the aluminum crank but it will move,
either at the washer to pedal spindle interface or between the
washer and crank. That motion will have a crack generating effect
on the most highly loaded threads near the washer and can generate
cracks just the same. This feature only hides the effect. It's a
Bandaid(R).
Just the same, I find interesting that TA recognized the presence
of a problem without analyzing effect it has and how to fix it.
Discussing this with crank/pedal manufacturers is a tricky subject.
I am amazed at all the slippery dodges they can muster in defense
of current practice.

Thank you. I anticipated the general direction of your analysis.
There is no "washer to pedal spindle interface" as you wrote. What
you are calling a "washer" is in fact a flange on the pedal
spindle/threaded-bolt element; they are all one piece of steel. The
flange sits inside a counter sunk area on the crank face. Is this
how you see the diagram?

Whether it is attached or not won't make any difference, the radial
fit in the recess is not a press fit and will fret radially as pedal
forces push it across its contact face. I have seen washers used in
this place that just created another interface but did not prevent
motion at the face and in the spindle threads.

***@stanfordalumni.org

chalo colina

2005-05-16 01:23:14 UTC

Post by j***@stanfordalumni.org
Whether it is attached or not won't make any difference, the radial
fit in the recess is not a press fit and will fret radially as pedal
forces push it across its contact face. I have seen washers used in
this place that just created another interface but did not prevent
motion at the face and in the spindle threads.

It seems to me that if the washer has a significantly higher
coefficient of friction on the crank than on the pedal spindle, then
the movement and therefore the fretting will occur at the interface
between washer and spindle, and not at the crank.

I have not tried pedal washers, because I have yet to crack a pedal
eye. Of course, I don't use feeble spindly cranks either.

In my opinion, a man your size who puts in as many miles as you do
should probably be riding tubular steel cranks.

Chalo Colina

j***@stanfordalumni.org

2005-05-16 18:23:17 UTC

Post by j***@stanfordalumni.org
Whether it is attached or not won't make any difference, the radial
fit in the recess is not a press fit and will fret radially as
pedal forces push it across its contact face. I have seen washers
used in this place that just created another interface but did not
prevent motion at the face and in the spindle threads.

So? As I said, the damage is not only the face of the crank, but
fretting in the threads. Besides, the washers on TA cranks I have
seen squish out into a slight cup shape beyond the diameter of the
spindle face and do not protect the crank face. The only difference
is that the crank face is already countersunk when new.

Post by chalo colina
I have not tried pedal washers, because I have yet to crack a pedal
eye. Of course, I don't use feeble spindly cranks either.
In my opinion, a man your size who puts in as many miles as you do
should probably be riding tubular steel cranks.

From what you have written, you weigh a substantial bit more than I.

***@stanfordalumni.org

d***@yahoo.com

2005-05-16 21:12:32 UTC

http://sargentwelch.com/product.asp_Q_pn_E_WLC94153%2D04%5FEA_A_Iron_E_

is this stuff in locktite's prep solution? floatin Fe ions?

Luns Tee

2005-05-16 23:32:24 UTC

Post by j***@stanfordalumni.org
So? As I said, the damage is not only the face of the crank, but
fretting in the threads. Besides, the washers on TA cranks I have
seen squish out into a slight cup shape beyond the diameter of the
spindle face and do not protect the crank face. The only difference
is that the crank face is already countersunk when new.

I do find myself wondering though, if the washers may still
have some marginal value to them. I would expect that having an aluminum
washer fretting against the crank face would be better for the crank
than a hard steel spindle face doing the fretting - the softer washer
would sacrificially take its share of erosion rather than let the
crank face take it all.

Also, I'd expect any cracks that intiated at the washer/spindle
interface, even if they propogate through the washer, to not make it
through the washer/crank interface - this reminiscent of the
difference in crack behaviour between fibreglass composites and solid glass.

Of course, as pointed out, washers still do absolutely nothing
to mitigate fretting in the threads.

That TA offers these washers, and the recess for them would
indicate they at least acknowledge there's an issue here. Perhaps they
would be more receptive to suggestions here than Shimano. Too bad they
don't have much market share here in the US.

-Luns

j***@stanfordalumni.org

2005-05-17 04:02:27 UTC

Post by j***@stanfordalumni.org
So? As I said, the damage is not only the face of the crank, but
fretting in the threads. Besides, the washers on TA cranks I have
seen squish out into a slight cup shape beyond the diameter of the
spindle face and do not protect the crank face. The only
difference is that the crank face is already countersunk when new.

I do find myself wondering though, if the washers may still have
some marginal value to them. I would expect that having an aluminum
washer fretting against the crank face would be better for the crank
than a hard steel spindle face doing the fretting - the softer
washer would sacrificially take its share of erosion rather than let
the crank face take it all.
Also, I'd expect any cracks that initiated at the washer/spindle
interface, even if they propagate through the washer, to not make it
through the washer/crank interface - this reminiscent of the
difference in crack behaviour between fibreglass composites and solid glass.
Of course, as pointed out, washers still do absolutely nothing to
mitigate fretting in the threads.
That TA offers these washers, and the recess for them would indicate
they at least acknowledge there's an issue here. Perhaps they would
be more receptive to suggestions here than Shimano. Too bad they
don't have much market share here in the US.

I don't have much hope for that. Having discussed this with many
crank folks at InterBike and receiving either blank stares from
engineers who don't understand what I am demonstrating and explaining
to the ones who don't think anyone knows more about cranks than they
and have never seen a crank failure like this.

This is typical for the bicycle industry as I have experienced it over
the last decades. Shimano is an extreme case.

***@stanfordalumni.org

Sandy

2005-05-17 09:31:41 UTC

Post by j***@stanfordalumni.org
I don't have much hope for that. Having discussed this with many
crank folks at InterBike and receiving either blank stares from
engineers who don't understand what I am demonstrating and explaining
to the ones who don't think anyone knows more about cranks than they
and have never seen a crank failure like this.
This is typical for the bicycle industry as I have experienced it over
the last decades. Shimano is an extreme case.

How much of a cone angle would it take to make the change you suggest ? Is
it radical, or mild, to achieve the effect you are aiming at ?

--
Bonne route,

Sandy
Verneuil-sur-Seine FR

j***@stanfordalumni.org

2005-05-17 16:45:20 UTC

Post by Sandy

Post by j***@stanfordalumni.org
I don't have much hope for that. Having discussed this with many
crank folks at InterBike and receiving either blank stares from
engineers who don't understand what I am demonstrating and
explaining to the ones who don't think anyone knows more about
cranks than they and have never seen a crank failure like this.
This is typical for the bicycle industry as I have experienced it
over the last decades. Shimano is an extreme case.

How much of a cone angle would it take to make the change you
suggest? Is it radical, or mild, to achieve the effect you are
aiming at?

http://pardo.net/bike/pic/fail-001/FAIL-016.html

The effect is the same as that of conical lug nuts on car wheels, that
of centering and load carried in compression rather than shear. It
prevents fretting motions that cause wear and unscrewing of right hand
threads on left pedals or the converse for right pedals... that is to
say, left hand threads for left pedals would not be required.

***@stanfordalumni.org

jim beam

2005-05-18 12:56:01 UTC

Post by Sandy

Post by j***@stanfordalumni.org
I don't have much hope for that. Having discussed this with many
crank folks at InterBike and receiving either blank stares from
engineers who don't understand what I am demonstrating and
explaining to the ones who don't think anyone knows more about
cranks than they and have never seen a crank failure like this.
This is typical for the bicycle industry as I have experienced it
over the last decades. Shimano is an extreme case.

How much of a cone angle would it take to make the change you
suggest? Is it radical, or mild, to achieve the effect you are
aiming at?

http://pardo.net/bike/pic/fail-001/FAIL-016.html
The effect is the same as that of conical lug nuts on car wheels, that
of centering and load carried in compression rather than shear. It
prevents fretting motions that cause wear and unscrewing of right hand
threads on left pedals or the converse for right pedals... that is to
say, left hand threads for left pedals would not be required.

so, based on your research, what effect does the interface angle have on
the effect you're trying to achieve?

Joe Riel

2005-05-18 17:59:43 UTC

[...]

Post by j***@stanfordalumni.org
prevents fretting motions that cause wear and unscrewing of right hand
threads on left pedals or the converse for right pedals... that is to
say, left hand threads for left pedals would not be required.

so, based on your research, what effect does the interface angle have on
the effect you're trying to achieve?

For a given bolt tension, the torque required to unscrew the joint is

tau1 = mu*T*R/cos(theta)

where

T = bolt tension
tau = required torque to unscrew
mu = coefficient of friction (steel to aluminum)
R = average radius of taper
theta = angle of taper (0 is the usual)

With theta = pi/4 (Jobst's modification) the relative torque
is increased from 1 to sqrt(2) ~ 41%.

Suppose we model the interface as a ball joint and then compute the
torque required to make the joint rotate in the plane in which the
spindle lies. Note that this torque is orthogonal to the unscrewing
torque. The required torque is then

tau2 = 2*mu*T*R/sin(2*theta)

This is a minimum at theta = pi/4! However, this model is too
simplistic. It predicts an infinite torque is required with a
standard spindle (theta = 0) because the lever arm goes to infinity.

Joe Riel

c***@comcast.net

2005-05-18 19:03:03 UTC

On Wed, 18 May 2005 17:59:43 GMT, Joe Riel

Post by Joe Riel
[...]

so, based on your research, what effect does the interface angle have on
the effect you're trying to achieve?

For a given bolt tension, the torque required to unscrew the joint is

[snip unscrewing equations]

Dear Joe,

Is the torque required to unscrew the joint the same as
fretting?

That is, do the pedals actually unscrew from the crank in
this situation and then screw back in, remaining in the same
place forever?

I'm not arguing, just not clear on the motion.

Is it rotary from the point of view of the pedal shaft, like
a bolt being turned by a wrench, with an X on the bolt head
rotating?

Or is it more a bending motion, like a fence-post set in
concrete being pushed back and forth, with an X on the top
of the fence post not rotating when viewed from above, but
moving off-center to one side?

Carl Fogel

j***@stanfordalumni.org

2005-05-18 19:22:00 UTC

Is the torque required to unscrew the joint the same as fretting?
That is, do the pedals actually unscrew from the crank in this
situation and then screw back in, remaining in the same place
forever?

The pedal spindle is displaced as you would expect a steel pin in a
stiff rubber crank bore. It skews and precesses but cannot tighten
farther than it is because it is bearing on the crank face with a flat
shoulder. As the crank face erodes from fretting, the pedal screws in
as much as this loss of length predicts plus the erosion on the thread
faces that hold the pedal in place.

This moving thread interface is about as dirty as you can imagine. As
many of us have found, the wear debris makes the pedal almost
un-removable and about these we read here off and on. That is why the
most benign removal is done by heating the crank on a gas flame until
it sizzles to the wet finger.

Is it rotary from the point of view of the pedal shaft, like a bolt
being turned by a wrench, with an X on the bolt head rotating?

It would like to but because it is already hard up against the crank
face, it cannot advance farther. The main motion is a radial offset
from the geometric center of spindle and crank thread.

Or is it more a bending motion, like a fence-post set in concrete
being pushed back and forth, with an X on the top of the fence post
not rotating when viewed from above, but moving off-center to one
side?

Since these are metals and metals are elastic, there is always some
bending taking place, but in this interface the radial displacement is
the main culprit.

***@stanfordalumni.org

c***@comcast.net

2005-05-18 19:49:24 UTC

On Wed, 18 May 2005 19:22:00 GMT,

Is the torque required to unscrew the joint the same as fretting?
That is, do the pedals actually unscrew from the crank in this
situation and then screw back in, remaining in the same place
forever?

The pedal spindle is displaced as you would expect a steel pin in a
stiff rubber crank bore. It skews and precesses but cannot tighten
farther than it is because it is bearing on the crank face with a flat
shoulder. As the crank face erodes from fretting, the pedal screws in
as much as this loss of length predicts plus the erosion on the thread
faces that hold the pedal in place.
This moving thread interface is about as dirty as you can imagine. As
many of us have found, the wear debris makes the pedal almost
un-removable and about these we read here off and on. That is why the
most benign removal is done by heating the crank on a gas flame until
it sizzles to the wet finger.

Is it rotary from the point of view of the pedal shaft, like a bolt
being turned by a wrench, with an X on the bolt head rotating?

It would like to but because it is already hard up against the crank
face, it cannot advance farther. The main motion is a radial offset
from the geometric center of spindle and crank thread.

Since these are metals and metals are elastic, there is always some
bending taking place, but in this interface the radial displacement is
the main culprit.

Dear Jobst,

So it's more two pieces rattling against each other than a
rotary motion between the two faces.

(Plus the tiny bit of tightening of the thread that you
point out will occur as the faces wear away.)

I'll try to think of it as a microscopic version of a
rattlesnake's rattle, where the buttons rock back and forth
at the joints, but don't twist relative to each other.

Thanks for explaining it (again),

Carl Fogel

Joe Riel

2005-05-18 20:39:19 UTC

Post by j***@stanfordalumni.org
Since these are metals and metals are elastic, there is always some
bending taking place, but in this interface the radial displacement is
the main culprit.

So the idea behind the "chamfer" is to convert a radial displacement
into an axial displacement that increases the screw tension, hence
reduces the movement.

Joe

j***@stanfordalumni.org

2005-05-18 22:49:18 UTC

Post by Joe Riel

Post by j***@stanfordalumni.org
Since these are metals and metals are elastic, there is always some
bending taking place, but in this interface the radial displacement
is the main culprit.

So the idea behind the "chamfer" is to convert a radial displacement
into an axial displacement that increases the screw tension, hence
reduces the movement.

Visualize the spindle as having a node in the middle of the tread
about which the spindle yaws in rotation. The outer end of the
spindle is not restrained from moving radially except by friction of
the plane shoulder of the spindle that is screwed tight against the
face of the crank.

With the conical seat, as with lug nuts on cars, radial loads can be
transmitted in compression between spindle and crank. A flat face
cannot do that nor can a cylindrical one without a radial preload
(press fit). That's why the square taper BB spindle is tapered. A
conical seat takes care of furnishing preload and carrying the canting
load in compression.

***@stanfordalumni.org

Jim Smith

2005-05-18 23:17:09 UTC

Is the torque required to unscrew the joint the same as fretting?
That is, do the pedals actually unscrew from the crank in this
situation and then screw back in, remaining in the same place
forever?

How does the initial tightness of the pedal affect this situation?
From your description is sounds as if there will always be some wear
and further turning of the pedal in the crank. Does this lead all
pedal/cranks to eventually end up in the same state, or am I
misunderstanding something?

Joe Riel

2005-05-18 20:33:09 UTC

Post by c***@comcast.net
Is the torque required to unscrew the joint the same as
fretting?
That is, do the pedals actually unscrew from the crank in
this situation and then screw back in, remaining in the same
place forever?

Good question. I don't claim to understand what is going on,
just making a few computations based on a simplistic model.

Given that with normal pedals there is no unscrewing torque
(the "precession" torque causes the spindles to tighten),
my first computation is pointless.

The more interesting computation is the second, where I make a
reckless attempt to estimate how Jobst's conical design may reduce the
presumed rocking/fretting motion caused by the cyclical load.
However, the model is clearly wrong, the fretting motion doesn't, I
think, cause a rocking motion that can be modeled as a ball joint, if
anything the the pivot is on the other side (i.e. through crankarm).
In which case the motion is more sliding/distorting. I'm not sure
that there is a simple way to model this.

Post by c***@comcast.net
Or is it more a bending motion, like a fence-post set in
concrete being pushed back and forth, with an X on the top
of the fence post not rotating when viewed from above, but
moving off-center to one side?

I believe that that is a reasonable approximation.

Joe

jim beam

2005-05-19 01:17:30 UTC

Post by Joe Riel

Good question. I don't claim to understand what is going on,
just making a few computations based on a simplistic model.
Given that with normal pedals there is no unscrewing torque
(the "precession" torque causes the spindles to tighten),
my first computation is pointless.
The more interesting computation is the second, where I make a
reckless attempt to estimate how Jobst's conical design may reduce the
presumed rocking/fretting motion caused by the cyclical load.
However, the model is clearly wrong, the fretting motion doesn't, I
think, cause a rocking motion that can be modeled as a ball joint, if
anything the the pivot is on the other side (i.e. through crankarm).
In which case the motion is more sliding/distorting. I'm not sure
that there is a simple way to model this.

the angled interface merely migrates the rocking pivot point from about
the middle of the spindle thread to the shamfer itself.

Post by Joe Riel

I believe that that is a reasonable approximation.
Joe

Jasper Janssen

2005-05-23 12:54:15 UTC

Post by j***@stanfordalumni.org
The effect is the same as that of conical lug nuts on car wheels, that
of centering and load carried in compression rather than shear. It
prevents fretting motions that cause wear and unscrewing of right hand
threads on left pedals or the converse for right pedals... that is to
say, left hand threads for left pedals would not be required.

Would this then be a good mod to do on
regular-cranksets-converted-for-tandem-use?

Jasper

Ryan Cousineau

2005-05-23 17:59:19 UTC

Post by Jasper Janssen

Would this then be a good mod to do on
regular-cranksets-converted-for-tandem-use?
Jasper

Oohhhh Jasper, I like the way you think. Except for one thing: for
non-machinists, it's probably still cheaper to find used tandem cranks
than to get someone to make the modifications.

Back to Sheldon's ghetto tandem design for us,

--
Ryan Cousineau ***@sfu.ca http://www.wiredcola.com/
"I don't want kids who are thinking about going into mathematics
to think that they have to take drugs to succeed." -Paul Erdos

j***@stanfordalumni.org

2005-05-23 22:30:47 UTC

Post by Jasper Janssen

Post by j***@stanfordalumni.org
The effect is the same as that of conical lug nuts on car wheels,
that of centering and load carried in compression rather than
shear. It prevents fretting motions that cause wear and unscrewing
of right hand threads on left pedals or the converse for right
pedals... that is to say, left hand threads for left pedals would
not be required.

Would this then be a good mod to do on

regular-cranks-converted-for-tandem-use?

It's good improvement on any current cranks but that would also solve
the right/left thread problem for a tandem. The trouble is that it
isn't a trivial machining operation and the pedal thread relief must
be cylindrical. My point is that manufacturers could easily do this,
having control over the pedal spindle dimensions. Countersinking a
crank eye in the center of its thread is not easily done because the
center is unknown and must be found.

***@stanfordalumni.org

f***@yahoo.com

2005-05-24 00:03:55 UTC

Post by j***@stanfordalumni.org
Countersinking a
crank eye in the center of its thread is not easily done because the
center is unknown and must be found.

How did you accurately locate that countersink?

- Frank Krygowski

j***@stanfordalumni.org

2005-05-24 00:26:38 UTC

Post by f***@yahoo.com

Countersinking a crank eye in the center of its thread is not
easily done because the center is unknown and must be found.

How did you accurately locate that countersink?

I relied on my machine shop that does this sort of thing often. I
think he threaded in a pseudo pedal shaft that had a true center and
fit the threads tightly. The collet must have an ID that is
accurately the thread relief diameter on the pedal spindle and then
cut in half with a thin saw cut.

***@stanfordalumni.org

jim beam

2005-05-17 13:09:53 UTC

Post by j***@stanfordalumni.org
So? As I said, the damage is not only the face of the crank, but
fretting in the threads. Besides, the washers on TA cranks I have
seen squish out into a slight cup shape beyond the diameter of the
spindle face and do not protect the crank face. The only
difference is that the crank face is already countersunk when new.

I do find myself wondering though, if the washers may still have
some marginal value to them. I would expect that having an aluminum
washer fretting against the crank face would be better for the crank
than a hard steel spindle face doing the fretting - the softer
washer would sacrificially take its share of erosion rather than let
the crank face take it all.
Also, I'd expect any cracks that initiated at the washer/spindle
interface, even if they propagate through the washer, to not make it
through the washer/crank interface - this reminiscent of the
difference in crack behaviour between fibreglass composites and solid glass.
Of course, as pointed out, washers still do absolutely nothing to
mitigate fretting in the threads.
That TA offers these washers, and the recess for them would indicate
they at least acknowledge there's an issue here. Perhaps they would
be more receptive to suggestions here than Shimano. Too bad they
don't have much market share here in the US.

I don't have much hope for that. Having discussed this with many
crank folks at InterBike and receiving either blank stares from
engineers who don't understand what I am demonstrating and explaining
to the ones who don't think anyone knows more about cranks than they
and have never seen a crank failure like this.
This is typical for the bicycle industry as I have experienced it over
the last decades. Shimano is an extreme case.

what's this repeated assertion that fretting causes fatigue? you've
been saying that for years jobst, but just like "stress relief" it's
merely your assumption based on a somewhat limited understanding of
fatigue initiation. how on earth do you expect shimano to take you
seriously when, aside from the fact that you really do have some
substantial personality issues, you publish "engineering" material that
is so consistently & laughably incorrect? your "stress relief" theory
is based on assumptions about strain aging that don't exist in stainless
steels. such fundamental errors are just laughable. the fact that the
contradictions are published in your own book, and that you /still/
don't get the picture is just unbelievable. your only chance at any
credibility [if indeed that were to be possible] is to go back & correct
/all/ the serious errors in your publications, both dead tree & "faq",
then start being more civil to people. you could also try going to a
library occasionally.

your assumption that shimano are incompetent and incapable of employing
anything less than top flight engineers & metallurgists, ones that /do/
understand how to talk with each other [something clearly lacking in
certain quarters this side of the pacific] is simply ridiculous. the
fact that they spend their time addressing issues of actual concern
rather than getting side tracked with red herrings is a feather in their
cap, not a cause for your misplaced criticism.

chalo colina

2005-05-17 06:03:10 UTC

From what you have written, you weigh a substantial bit more than I.

And from what you have written, you have cracked a lot of pedal eyes.
That seems to me like a strong indication that your cranks are a poor
choice for you. There are stronger cranks available that won't crack
so readily.

Chalo Colina

j***@stanfordalumni.org

2005-05-17 16:37:18 UTC

Post by chalo colina
I have not tried pedal washers, because I have yet to crack a
pedal eye. Of course, I don't use feeble spindly cranks either.
In my opinion, a man your size who puts in as many miles as you do
should probably be riding tubular steel cranks.

I suppose you haven't seen the failure pictures of such cranks but
they don't give me any hope for more durability. They look more like
tin cans that were torn apart above the pedal eye. I don't have any
pictures but have seen them in the past. What brand do you have in
mind?

Post by j***@stanfordalumni.org
From what you have written, you weigh a substantial bit more than I.

And from what you have written, you have cracked a lot of pedal
eyes. That seems to me like a strong indication that your cranks
are a poor choice for you. There are stronger cranks available that
won't crack so readily.

Please don't keep it a secret. I have used Campagnolo Record and
Shimano Dura Ace, the latter having cracked at the pedal eye and in
the square taper. What cranks do you believe are more durable?

Meanwhile let's not overlook the failure mode, that of bending off at
the bottom of the stroke. You'll note that most of the pictures we
have seen and all the cranks I have broken show failure wave
propagation across the crank from outside to inside in bending mode.

The latest Ritchey failure posted here was the same even though it was
one of the "modern" shaped extra wide semi-channel shaped profiles.

***@stanfordalumni.org

Chalo

2005-05-18 01:32:49 UTC

Post by chalo colina
I have not tried pedal washers, because I have yet to crack a
pedal eye. Of course, I don't use feeble spindly cranks either.
In my opinion, a man your size who puts in as many miles as you do
should probably be riding tubular steel cranks.

I have put many hard miles on Bullseye cranks without the least
structural problem. I can't reasonably recommend them at this time,
though, as their bearings have undergone a design revision that i
suspect will not work in the long term.

Redline Flight cranks are impeccably made. They are offered in lengths
up to 190mm. To use them in a road bike, you'd have to fit it with a
threaded BB like the one from FSA.
http://www.danscomp.com/cgi-bin/hazel.cgi?action=DETAIL&item=451060
http://fullspeedahead.com/fly.aspx?layout=product&taxid=92&pid=117

FSA and Premium make nice sturdy tubular cranks that are not
offensively heavy, but they use an interference spline fit that I find
inferior to a pinch-bolted design.
http://fullspeedahead.com/fly.aspx?layout=product&taxid=88&pid=258
http://www.premiumbmx.com/cranks.html

Post by chalo colina
There are stronger cranks available that
won't crack so readily.

Please don't keep it a secret. I have used Campagnolo Record and
Shimano Dura Ace, the latter having cracked at the pedal eye and in
the square taper. What cranks do you believe are more durable?

I use Primo Powerbite cranks on most of my bikes. They use cold forged
7075 aluminum arms pinch-bolted to a 22mm spindle made of heat treated
4140 chromoly. There is a lighter titanium spindle available for them,
and they are offered with a threaded BB.
http://www.danscomp.com/cgi-bin/hazel.cgi?action=DETAIL&item=451057

Post by j***@stanfordalumni.org
Meanwhile let's not overlook the failure mode, that of bending off at
the bottom of the stroke. You'll note that most of the pictures we
have seen and all the cranks I have broken show failure wave
propagation across the crank from outside to inside in bending mode

All the cranks I have mentioned are much thicker through the arm at the
pedal boss than typical road bike cranks. They are also made of higher
yield stress materials than road bike cranks. It's no mystery why they
hold up better with heavy use.

Chalo Colina

c***@comcast.net

2005-05-18 02:46:08 UTC

On Tue, 17 May 2005 16:37:18 GMT,
***@stanfordalumni.org wrote:

[snip]

I suppose you haven't seen the failure pictures of such [tubular
steel] cranks but >they don't give me any hope for more durability.
They look more like >tin cans that were torn apart above the pedal
eye. I don't have any pictures but have seen them in the past.

[snip]

Dear Jobst,

While not pedal eye failures, these are pictures of tubular
cranks that failed:

A failed Bullseye crank:

http://pardo.net/bike/pic/fail-001/FAIL-002.html

Three pictures of a failed Tioga Revolver crank:

http://pardo.net/bike/pic/fail-001/FAIL-003.html

(The third picture on the page above shows the "tin cans
that were torn apart" notion, but that's merely what to
expect from such hollow failures--a solid crank looks like a
piece of snapped chalk when it breaks.)

Carl Fogel

f***@yahoo.com

2005-05-17 01:44:02 UTC

ISTR you're not a Loctite fan, Jobst. Nonetheless, I wonder if a
strong Loctite compound would help if it were used to bond the washer
to the crank face.

I also wonder if a super-weak Loctite formula would help on the pedal
threads themselves...

Come to think of it, the pedal threads don't need the adhesion of
loctite, since (in my experience) they're generally quite difficult to
remove as is. But they might benefit from something to fill the
clearance, as Loctite does, and reduce the motion that causes the
fretting. Perhaps teflon tape? It's done wonders for my bottom
bracket.

All in all, I think your countersunk pedal interface is a superior
solution, but it's much more difficult to apply to the millions of
existing cranks. A loctited washer and some teflon tape might be a
feasible shop solution.

- Frank Krygowski - (who's never broken a crank)

j***@stanfordalumni.org

2005-05-17 04:14:02 UTC

Post by f***@yahoo.com

Post by j***@stanfordalumni.org
Whether it is attached or not won't make any difference, the radial
fit in the recess is not a press fit and will fret radially as
pedal forces push it across its contact face. I have seen washers
used in this place that just created another interface but did not
prevent motion at the face and in the spindle threads.

ISTR you're not a Loctite fan, Jobst. Nonetheless, I wonder if a
strong Loctite compound would help if it were used to bond the
washer to the crank face.

Loctite doesn't work with adhesion but rather with crack filling
abilities. Its resulting solid form is not nearly as strong as the
metals involved in this interface and soon becomes just so much fine
dust in the joint. Loctite works best in area contacts such as
cylindrical fits (bearing OD etc) but the pedal eye is a classic shear
force at high load.

Post by f***@yahoo.com
I also wonder if a super-weak Loctite formula would help on the
pedal threads themselves...

If tightening the spindle as much as you can doesn't retard this
action, how do you expect Loctite to do it?

Post by f***@yahoo.com
Come to think of it, the pedal threads don't need the adhesion of
Loctite, since (in my experience) they're generally quite difficult to
remove as is. But they might benefit from something to fill the
clearance, as Loctite does, and reduce the motion that causes the
fretting. Perhaps Teflon tape? It's done wonders for my bottom
bracket.

That's not any help in keeping them from unscrewing on tandems that on
occasion used conventional cranks for the transfer chain, right hand
thread on the left, left hand thread on the right. They work loose.

Post by f***@yahoo.com
All in all, I think your countersunk pedal interface is a superior
solution, but it's much more difficult to apply to the millions of
existing cranks. A Loctited washer and some Teflon tape might be a
feasible shop solution.

Forget about existing equipment. If Shimano can ignore past cranks
and BB's they can do it for pedals as well.

***@stanfordalumni.org

f***@yahoo.com

2005-05-17 05:05:32 UTC

Post by f***@yahoo.com
ISTR you're not a Loctite fan, Jobst. Nonetheless, I wonder if a
strong Loctite compound would help if it were used to bond the
washer to the crank face.

I recall a machinist who loctited a coin (a quarter?) to a steel
surface as a joke. It seemed to work well enough in that situation.
Seems to me it merely has to produce an effective coefficient of
friction higher than that on the non-loctite side of the washer, no? I
think the stronger grades are easily capable of that.

Post by f***@yahoo.com
I also wonder if a super-weak Loctite formula would help on the
pedal threads themselves...

If tightening the spindle as much as you can doesn't retard this
action, how do you expect Loctite to do it?

As you said, Loctite fills the gap between components, then solidifies.
Filling the gap is supposedly at least as important as its adhesive
qualities. A thread under tension and subjected to vibratory movement
slides "downhill," just as an object sitting on an incline slides
downhill when pushed sideways.

If the pedal is prevented from moving in the crank by the filling of
the clearance space, you wouldn't get the precession-like wiggling
motion, which is analogous to the sideways motion of an object on an
incline.

Are you saying loctite doesn't help cranks reversed for tandem duty? I
was under the impression it does. I haven't heard of anyone trying
just teflon tape in that application, but I wouldn't either. I'd
expect the gap filling, motion-stopping action of Loctite to be much
better.

Forget about existing equipment. If Shimano can ignore past cranks
and BB's they can do it for pedals as well.

No doubt. But there'd still be millions of cyclists with the old
stuff. Many would appreciate a procedure that provided cheap
insurance.

- Frank Krygowski

d***@yahoo.com

2005-05-17 20:52:37 UTC