broken crank (was: crank crack)
Tom Paterson
http://technology.open.ac.uk/materials/mem/mem-ccf4.html
Good one there (IMHO)! Looks like the common Campagnolo "spider crack" might
have found full expression on this crank. --Tom Paterson
jobst....@stanfordalumni.org
> http://technology.open.ac.uk/materials/mem/mem-ccf4.html
> Good one there (IMHO)! Looks like the common Campagnolo "spider
> crack" might have found full expression on this crank.
Nice picture. I've had cranks like that.
This is a common failure and the one most easily prevented but the
bicycle industry doesn't want to bother. One solution is to take the
Campagnolo C-Record approach and make the crank one of the five spider
arms. Ritchey cranks do that also. Shimano doesn't do that because
their cranks are hollow and might crack from the chainring bolt
entering the hollow crank. However, with the crank in the picture,
Campagnolo and others who use this design need only to machine away
the thin web between spider and both sides of the crank so that it no
longer looks like the skin between index and middle finger spread
apart.
Jobst Brandt
jobst....@stanfordalumni.org
Palo Alto CA
jt
<jobst....@stanfordalumni.org> wrote in message
news:xKCya.15692$JX2.9...@typhoon.sonic.net...
>
> This is a common failure and the one most easily prevented but the
> bicycle industry doesn't want to bother. One solution is to take the
> Campagnolo C-Record approach and make the crank one of the five spider
> arms. Ritchey cranks do that also. Shimano doesn't do that because
> their cranks are hollow and might crack from the chainring bolt
> entering the hollow crank. However, with the crank in the picture,
> Campagnolo and others who use this design need only to machine away
> the thin web between spider and both sides of the crank so that it no
> longer looks like the skin between index and middle finger spread
> apart.
>
Dremel.
Or needle file and about 20 minutes...
Scic
>However, with the crank in the picture,
>Campagnolo and others who use this design need only to machine away
>the thin web between spider and both sides of the crank so that it no
>longer looks like the skin between index and middle finger spread
>apart.
Hmmm...just curious. Your statement seems to suggest that the web can
contribute to a crank's failure rather than its strength. How is this so?
Sig
Chicago
jobst....@stanfordalumni.org
>> However, with the crank in the picture, Campagnolo and others who
>> use this design need only to machine away the thin web between
>> spider and both sides of the crank so that it no longer looks like
>> the skin between index and middle finger spread apart.
> Hmmm... just curious. Your statement seems to suggest that the web
> can contribute to a crank's failure rather than its strength. How
> is this so?
Thin webs that are at the extremes of a bending element carry many
times the stress of the main member. That is why I-beams have thick
flat "caps" connected by a thin web less than half the thickness of
the caps. Cutting the beam in half lengthwise through the web and
putting the caps back to back so that the half-webs are outermost is
what we have in the crank. Structural engineers are aware of this but
the bicycle industry is not.
In the collection of failed cranks, we also see evidence of failures
at embossed or cast-in logos. Formerly, most cranks had a lengthwise
vanity groove on the outside that reduced crank stiffness by at least
30%. There are still I-beam like cranks on the market even though
this shape has notoriously poor torsional stiffness. It may be a
fashion statement because many people recognize the I-bean shape and
think cranks are stressed mainly in bending. Failures are as much
from torsion as bending. Where do these guys go to school, if at all?
http://pardo.net/pardo/bike/pic/fail/FAIL-001.html
Matt O'Toole
<jobst....@stanfordalumni.org> wrote in message
news:8qSya.15901$JX2.9...@typhoon.sonic.net...
Art school.
Matt O.
Andy Dingley
wrote:
>Where do these guys go to school, if at all?
Sloan ?
The bike trade is about selling things, not making things. If you want
to see a better crank, try educating the bike mag journos who rave
about a product, despite some obvious design horror (certainly for the
UK MTB scene).
When a logo is seen as a fashionable branding, then it's going to be
on there. Only when the punter starts to see it as a potential stress
riser, and not buy the product, will they disappear.
jobst....@stanfordalumni.org
>> Where do these guys go to school, if at all?
> Sloan?
> The bike trade is about selling things, not making things. If you
> want to see a better crank, try educating the bike magazine
> journalists who rave about a product, despite some obvious design
> horror (certainly for the UK MTB scene).
> When a logo is seen as a fashionable branding, then it's going to be
> on there. Only when the punter starts to see it as a potential
> stress riser, and not buy the product, will they disappear.
I still have hope for Shimano. Their DA cranks no longer have a
vanity groove, they don't emboss their logo and they are continuing in
their pursuit of a reliable and easy to install BB. The current ones
don't meet that criterion and that's why we see the one on the Lance
Armstrong bicycle with the double pinch-bolt cranks. They may be
thinking about pedal attachment on the back burner.
http://www.lancearmstrong.com/lance/OnLine2.nsf/Docs/D37499CB86AB278C86256D15006F21CD
Qui si parla Campagnolo
to see a better crank, try educating the bike mag journos who rave
about a product, despite some obvious design horror (certainly for the
UK MTB scene)
on there. Only when the punter starts to see it as a potential stress
riser, and not buy the product, will they disappear.
Reality, what a concept....
Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
Richard Chan
>... Their DA cranks no longer have a vanity groove, they don't emboss
their logo and they are continuing in their pursuit of a reliable and
easy to install BB. ...>
I haven't follow bike trends for ~ 10 years. When was the last
generation that Shimano cranks have "vanity" grooves? In the 70s?
Chris Zacho The Wheelman
"I haven't follow bike trends for ~ 10 years. When was the last
generation that Shimano cranks have "vanity" grooves? In the 70s? "
The Dura Ace cranks I bought in '77 for my Lygie had "vanity grooves"
They started disappearing round the early eighties.
Whether that was for engineering reasons or just fashion change, I don't
know. My Sugino AT (which I bought in 84) doesn't have them.
It's name is lightly embossed into the arms though.
May you have the wind at your back.
And a really low gear for the hills!
Chris
Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner
A Muzi
news:<IAVya.15938$JX2.9...@typhoon.sonic.net>...
>
> >... Their DA cranks no longer have a vanity groove, they don't emboss
> their logo and they are continuing in their pursuit of a reliable and
> easy to install BB. ...>
"Richard Chan" <a019...@yahoo.com> wrote in message
news:81ba5168.03052...@posting.google.com...
> I haven't follow bike trends for ~ 10 years. When was the last
> generation that Shimano cranks have "vanity" grooves? In the 70s?
The Dura Ace EX before it became New Dura Ace (7400) in 1983?4?
--
Andrew Muzi
http://www.yellowjersey.org
Open every day since 1 April 1971