Straightening a bent Dura Ace crank arm
Jpinkowish
Patient is a 7400 square taper left crank arm, 170mm, absolutely no scratching,
scuffs, or dings.
Off the bike and next to an unbent arm, the pedal end of this crank arm is bent
inward(toward the chain stay) about 3-4mm from a single impact.
I know the arm is aluminum. There's got to be a way to safely move this thing.
Comments???
Jan Pinkowish
Alex Rodriguez
says...
I recall seeing in the Loose Screws catalog a tool that could be used to
straighten crank arms. Basically a large lever. If I was to do this, I
would examine the crank arm on a regular basis to see if any cranks were
forming.
-----------------
Alex __O
_-\<,_
(_)/ (_)
Sheldon Brown
If you do straighten it, I would advise wearing a titanium cup when you
ride.
Sheldon "Don't Do It" Brown
+-----------------------------------------+
| If a fool would persist in his folly, |
| he would become wise. |
| --William Blake |
+-----------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
jobst....@stanfordalumni.org
>> I know you're not supposed to, but... Patient is a 7400 square
>> taper left crank arm, 170mm, absolutely no scratching, scuffs, or
>> dings.
>> Off the bike and next to an unbent arm, the pedal end of this crank
>> arm is bent inward(toward the chain stay) about 3-4mm from a single
>> impact. I know the arm is aluminum. There's got to be a way to
>> safely move this thing.
> I recall seeing in the Loose Screws catalog a tool that could be used to
> straighten crank arms. Basically a large lever. If I was to do this, I
> would examine the crank arm on a regular basis to see if any cranks were
> forming.
Aieeeee... Banzai!
Can't we just say "crank". Where did we get this "crank arm"
or "cranks arm set" yet?
Webster's Dictionary:
Crank:
1 : a bent part of an axle or shaft or an arm keyed at right angles to
the end of a shaft by which circular motion is imparted to or received
from the shaft or by which reciprocating motion is changed into
circular motion or vice versa
Jobst Brandt
jobst....@stanfordalumni.org
Palo Alto CA
Derk
> If you do straighten it, I would advise wearing a titanium cup when you
> ride.
:-)
OUCH!
Greets, Derk
DiabloScott
Sure, but you should heat it up first so it doesn't crack - 900 Kelvin
ought to be enough. T(mp)=933K
--
Check out my bike blog!
http://diabloscott.blogspot.com
Check out my bike blog!
http://diabloscott.blogspot.com
>--------------------------<
Posted via cyclingforums.com
http://www.cyclingforums.com
jobst....@stanfordalumni.org
> If you do straighten it, I would advise wearing a titanium cup when
> you ride.
The same sentiment was expressed when Lance Armstrong landed with his
foot on the road as his gear shift while standing failed.
Those who repeat this admonition probably haven't observed such a
failure and are imagining the result. Such failures occur under load
while standing on one pedal. In this position the rider does not land
with crotch centered on the top tube as one might imagine. It did not
happen in the TdF and I can vouch for that having broken about 30
Campagnolo and Shimano cranks in my cycling career, most occurring
while standing.
You'll note that Lance was uninjured and got back in the pedals with
practically no loss of time.
Sheldon, please add this to your myth and lore collection.
Chalo
> Can't we just say "crank". Where did we get this "crank arm"
> or "cranks arm set" yet?
How would you propose to distinguish between a single arm and the pair
or the assembly? How would you distinguish between a single arm and a
one-piece crank?
I think common usage in this case reflects the amount of distinction
most folks feel they need to make themselves correctly understood.
In automotive circles, the term "crank" is used interchangeably with
"crankshaft", though technically speaking those are not the same
thing. I've never heard anybody complain about that.
What I find confusing is this "chainset" business from Old Blighty.
There are no chains in a chainset, oddly enough.
Chalo Colina
jobst....@stanfordalumni.org
>> Can't we just say "crank". Where did we get this "crank arm" or
>> "cranks arm set" yet?
> How would you propose to distinguish between a single arm and the
> pair or the assembly? How would you distinguish between a single
> arm and a one-piece crank?
Just as you did in that paragraph. We have right cranks and left
cranks and both cranks and Ashtabula cranks and Shimano right cranks
w. spindle and left cranks.
> I think common usage in this case reflects the amount of distinction
> most folks feel they need to make themselves correctly understood.
A crank is a crank and adding arm sets is like the guys with the
sedans with spoilers on the trunk or Porsches whose trunk lid opens at
40mph. It's gratuitous verbiage that sounds like more than it is.
> In automotive circles, the term "crank" is used interchangeably with
> "crankshaft", though technically speaking those are not the same
> thing. I've never heard anybody complain about that.
So? This ain't cars and just because they have their problems doesn't
make ours any better. It's like cog in bicycling. It sounds so much
more IN than sprocket or chainwheel which say more than cog, which is
one tooth on the afore mentioned devices.
Webster's: COG
1 : a tooth on the rim of a wheel or gear
> What I find confusing is this "chainset" business from Old Blighty.
> There are no chains in a chainset, oddly enough.
Yes but it rings so much more like bicyclese than cranks or crank
assembly. Set theory has taken over.
The news is full of these enhanced words, roadway instead of road,
weather system in place of weather, heavy traffic conditions instead
of heavy traffic, rain showers instead of showers...
Phil Brown
>Sure, but you should heat it up first so it doesn't crack - 900 Kelvin
>ought to be enough. T(mp)=933K
Are you mad?
Phil Brown
jim beam
jan, *DO NOT* heat. for 3-4mm bend, you /might/ be able to get away
with cold setting it back, but you're going to need to keep it under
/real/ close observation afterwards.
the d/a cranks are cold forged and should be able to take it, but the
chance of /you/ being able to bend it back without introducing nicks,
scratches and other defects is small unless you have access to some
fancy tools.
jb
gwhite
jobst....@stanfordalumni.org wrote:
>
> Chalo Colina writes:
>
> >> Can't we just say "crank". Where did we get this "crank arm" or
> >> "cranks arm set" yet?
>
> > How would you propose to distinguish between a single arm and the
> > pair or the assembly? How would you distinguish between a single
> > arm and a one-piece crank?
crank (kràngk) noun
2. A clever turn of speech; a verbal conceit: quips and cranks.
3. A peculiar or eccentric idea or action.
4. Informal. a. A grouchy person. b. An eccentric person, especially one
who is unduly zealous.
The American Heritage® Dictionary of the English Language, Third Edition
copyright © 1992 by Houghton Mifflin Company. Electronic version
licensed from INSO Corporation. All rights reserved.
> The news is full of these enhanced words, roadway instead of road,
> weather system in place of weather, heavy traffic conditions instead
> of heavy traffic, rain showers instead of showers...
When I clean up after I ride, it doesn't mean I'm standing in the rain.
David L. Johnson
> Can't we just say "crank". Where did we get this "crank arm" or "cranks
> arm set" yet?
>
> Webster's Dictionary:
>
> Crank:
>
> 1 : a bent part of an axle or shaft or an arm keyed at right angles to the
> end of a shaft by which circular motion is imparted to or received from
> the shaft or by which reciprocating motion is changed into circular motion
> or vice versa
2: a person with a mental twist esp on some one subject
3: a bad-tempered person : GROUCH
Couldn't resist....
--
David L. Johnson
__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkien
Qui si parla Campagnolo
or the assembly? How would you distinguish between a single arm and a
WTF cares...was anybody confused? when the guy said crankset, arms, crank...
Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
Qui si parla Campagnolo
Lewis Campbell
>>>Webster's: COG
>
> 1 : a tooth on the rim of a wheel or gear <<<<
There is also a second definition, "A subordinate member of an
organization."
In LimeyLand, where I grew up and served my machine shop
apprenticeship, back in the 50's, we used the term 'cog' to refer to
the smaller gear, or gears, in a train.
Just last week they had an answer on Jeopardy, 'its a tooth on a
gear', the question being, 'what is a cog?' I almost called in to
correct them as I had caught them in an error once before but now I'm
glad I didn't.
However, I can now add this to a list of words that are perfect
English but do not mean the same thing on both sides of the pond.
:-)
Lewis.
************************************
jobst....@stanfordalumni.org wrote in message news:<LdQ3b.16601$dk4.5...@typhoon.sonic.net>...
jim beam
well, when you cold forge something, you have to do it within the limits
of the ductility of the material. and when you're done, a reliable
manufacturer will still have a margin of ductility left, otherwise the
material will be unusably brittle. for 3-4mm of deformation, depending
on exactly how it's bent, there should still be just enough ductility to
return it to original position and still have a /small/ safety margin.
this of course assumes that jan is being sensible and the original bend
is not all focussed on a weak spot like the spindle or pedal holes.
you are absolutely right in that the /ideal/ solution is to buy new &
start again, particularly if you don't have the skill or experience to
know what you're doing. but technically, if the deformation is within
the material's limits, there's no reason not to give it a go. i would
/not/ say this for anything other than high end components like the xtr
mentioned here.
jb
jobst....@stanfordalumni.org
>> Webster's: COG
>>
>> 1 : a tooth on the rim of a wheel or gear
> There is also a second definition, "A subordinate member of an
> organization."
That's an idiom derived from the Webster's definition of a gear having
cogs as subordinate elements.
> In LimeyLand, where I grew up and served my machine shop
> apprenticeship, back in the 50's, we used the term 'cog' to refer to
> the smaller gear, or gears, in a train.
That's the point. Jargon often obscures the true meaning of words and
the use of "cog" here in bicycling and among mechanics is widespread,
most of these folks not having any idea what a cog really is.
Cogwheel railways are a mystery to most folks for that reason.
http://tinyurl.com/lqej
http://tinyurl.com/lqeo
> Just last week they had an answer on Jeopardy, 'its a tooth on a
> gear', the question being, 'what is a cog?' I almost called in to
> correct them as I had caught them in an error once before but now
> I'm glad I didn't.
> However, I can now add this to a list of words that are perfect
> English but do not mean the same thing on both sides of the pond.
I assure you that the term and usage is the same in the USA and GB.
Qui si parla Campagnolo
/not/ say this for anything other than high end components like the xtr
I would not do it, nor would I rec. anybody else do this..For the cost of a new
crankarm, it just isn't worth having it break.
Phil Brown
>the material's limits, there's no reason not to give it a go. i would
>/not/ say this for anything other than high end components like the xtr
>
>mentioned here. >>
Sorry, by defination when aluminium bends it has exceeded its limit, unlike
steel.
Phil Brown
dianne_1234
Which limit are you thinking of?
Jim Beam has mentioned the limits of the ductility of the material,
which are clearly not exceeded yet, or the crank would be cracked.
Is there some other limit that bending aluminum exceeds? How do they
forge aluminum parts?
Not trying to be funny, I honestly don't know.
Phil Brown
>Is there some other limit that bending aluminum exceeds? How do they
>forge aluminum parts?
>
>Not trying to be funny, I honestly don't know.
There is the modulus of elestacisity and the yeild point, steels are far apart
and aluminium's very close. When alumium bends that's it it cal't be rebend.
Just try it with a piece of aluminium strip-bend it, try to straighten it and
you've broken it. Try it with steel and you can do it many times before it
breaks
Phil Brown
Dave
OK, this is not even close. Modulus of elasticity and yield point are
very different for all metals and comparing them is not meaningful here. I
can bend and rebend a lot of aluminum alloys in lots of forms (sheet,
plate, bar). Some steel will fracture before it yields significantly.
In general it is probably a bad idea to straighten aluminum alloy
parts on bicycles, but you can get away with it for most steel
parts. However, spreading metallurgical and mechanics nonsense that
happens to support these generally sound rules of thumb is not a good
thing.
On the other hand we have Jim Beam who is throwing around a lot of red
herrings that are technically correct, but generally irrelevant to the
problems being discussed.
I think I will stop reading this stuff and go ride,
Dave Korzekwa
jim beam
> parts on bicycles, but you can get away with it for most steel
> parts.
as a "rule of thumb", aluminum alloys are more ductile than steel. two
components reduced down to 10% ductility are both on the edge of
acceptibility whether they be steel /or/ aluminum.
> On the other hand we have Jim Beam who is throwing around a lot of red
> herrings that are technically correct, but generally irrelevant to the
> problems being discussed.
how so? the original poster wanted to know if it was possible to
straighten a crank with a /small/ bend. it /is/ technically possible!
by way of example, i guess the "red herringness" of that response
depends on whether you simply reinstall windows if your pc messes up, or
whether you get into the problem and manually fix it. just because
microsoft support charges you $60 to say "reinstall your system" doesn't
necessarily mean that's the /only/ solution for those with the skill &
knowledge to fix it another way.
Dave
> > In general it is probably a bad idea to straighten aluminum alloy
> > parts on bicycles, but you can get away with it for most steel
> > parts.
>
> as a "rule of thumb", aluminum alloys are more ductile than steel.
That's pretty broad statement, given the wide variety of steel and
aluminum alloys and processing methods. In the context of bike parts
it is usually true, but I don't think you want to straighten a bent
bottom bracket spindle (hardened steel). On the other hand,
straightening small dents in an aluminum rim does not usually lead to
failure.
> two components reduced down to 10% ductility are both on the edge of
> acceptability whether they be steel /or/ aluminum.
>
> > On the other hand we have Jim Beam who is throwing around a lot of red
> > herrings that are technically correct, but generally irrelevant to the
> > problems being discussed.
>
> how so? the original poster wanted to know if it was possible to
> straighten a crank with a /small/ bend. it /is/ technically possible!
> by way of example, i guess the "red herringness" of that response
> depends on whether you simply reinstall windows if your pc messes up,
> or whether you get into the problem and manually fix it. just because
> microsoft support charges you $60 to say "reinstall your system"
> doesn't necessarily mean that's the /only/ solution for those with the
> skill & knowledge to fix it another way.
You are assuming a lot here. It is highly unlikely that the aluminum
crank derives its strength from work hardening. It is probably a heat
treatable alloy, and any precipitation hardened Al alloy in a high
strength condition is almost certainly a poor candidate for
straightening. But my point is that you (and I) probably do not know
the alloy or processing history, so we don't know whether it is safe
to straighten the crank or not, even if we have it in our hands to
examine.
My gripe with your post is the implication that some sort of
forming/ductility limit related to cold working is the deciding
factor. Also, in my (admittedly limited) experience, XTR is
especially bad (or good?) at minimizing the weight at the expense of
durability. Cheaper parts are probably more likely to survive
straightening.
In other threads you seem to be taking the attitude that an
understanding of deep metallurgical principals is necessary to
understand and diagnose various bike part failures. You may have
something to contribute here. However, in my opinion you have been
attacking people unfairly based on what they may or may not know about
metallurgy that is, at best, peripheral to the technical issues.
Yes, I am a metallurgist, too. I hope that I am not coming across as
grumpy as Jobst.
Dave Korzekwa
jim beam
> crank derives its strength from work hardening. It is probably a heat
> treatable alloy, and any precipitation hardened Al alloy in a high
> strength condition is almost certainly a poor candidate for
> straightening. But my point is that you (and I) probably do not know
> the alloy or processing history, so we don't know whether it is safe
> to straighten the crank or not, even if we have it in our hands to
> examine.
afaik, 7400 series cranks are dural - forged & precipitation hardened.
and as a metallurgist, /you/ should be able to get a very good feel for
it's processing history just by looking. my old prof used to throw us
pieces of planes and have us tell him what it's processing history was
just by looking - even if we didn't know what the part was! if it's
machined, you know part of it's history. if it's forged, you know part
of it's history. if you look on shimano's web site, you know part of
it's history - or at least enough to make judgement based on your
experience of the available options!!!
> Also, in my (admittedly limited) experience, XTR is
> especially bad (or good?) at minimizing the weight at the expense of
> durability. Cheaper parts are probably more likely to survive
> straightening.
i don't agree with this - not for the cranks at any rate. my experience
has been that they are longer lasting and more abuse tolerant than
shimano's lesser models. that's not what a lot of people want to hear
because they like to bash the expense, but hey, that's another issue.
> in my opinion you have been
> attacking people unfairly based on what they may or may not know about
> metallurgy that is, at best, peripheral to the technical issues.
what kind of a statement is that???
just so you know, i /have/ straightened an xtr crank. with apparent
success. it's in weekly use by a friend and has been for the 2 years
since we worked on it. i take care to check it each time i see it, but
so far, so good. ymmv.
if someone writes into an open forum and starts dispensing "advice"
based on incorrect or incomplete data, then i don't see how they can
possibly expect to have a problem [assuming their ego allows] if someone
knows different. if you think i'm wrong, go ahead and say so - just as
long as you can to back it up. just don't expect bluster to be an
effective smokescreen that's all.
i chose my pc analogy carefully. the bike shop solution is to replace
the piece. it's quick, simple, and you can feel safe in the knowledge
that all the other bike shops will say the same thing - just go ahead &
reinstall windows.
/but/, if you can use the registry editor, or you know something like
"fdisk /mbr", i personally think it's worth exploring those options
before using the "one size fits all" remedy. but hey, i'm the guy that
fixed my car for the cost of a $15 relay when the dealer wanted $2,300
to replace the ecu & ignition system.
call me mean.
j
Dave
> > You are assuming a lot here. It is highly unlikely that the aluminum
> > crank derives its strength from work hardening. It is probably a heat
> > treatable alloy, and any precipitation hardened Al alloy in a high
> > strength condition is almost certainly a poor candidate for
> > straightening. But my point is that you (and I) probably do not know
> > the alloy or processing history, so we don't know whether it is safe
> > to straighten the crank or not, even if we have it in our hands to
> > examine.
>
> afaik, 7400 series cranks are dural - forged & precipitation
> hardened. and as a metallurgist, /you/ should be able to get a very
> good feel for it's processing history just by looking. my old prof
> used to throw us pieces of planes and have us tell him what it's
> processing history was just by looking - even if we didn't know what
> the part was! if it's machined, you know part of it's history. if
> it's forged, you know part of it's history. if you look on shimano's
> web site, you know part of it's history - or at least enough to make
> judgement based on your experience of the available options!!!
Interesting. Dural is a trade name. Do you know the AA alloy
designation? If it is precipitation hardened, then correctly designed
forging step should only improve the ductility, and as I stated, the
limits of ductility will not depend on that. If you can infer the
alloy and heat treatment by looking at a piece (especially without
knowing its function) then we could use you where I work. We usually
have to resort to costly analysis methods to get that information.
Being able to assess fatigue life after straightening a damaged part
is even more impressive.
>
> > Also, in my (admittedly limited) experience, XTR is
> > especially bad (or good?) at minimizing the weight at the expense of
> > durability. Cheaper parts are probably more likely to survive
> > straightening.
>
> i don't agree with this - not for the cranks at any rate. my
> experience has been that they are longer lasting and more abuse
> tolerant than shimano's lesser models. that's not what a lot of
> people want to hear because they like to bash the expense, but hey,
> that's another issue.
>
> > in my opinion you have been
> > attacking people unfairly based on what they may or may not know about
> > metallurgy that is, at best, peripheral to the technical issues.
>
> what kind of a statement is that???
Sorry, I was referring to other threads where you were bringing up
dislocations and such in the context of failure initiation. In those
cases, the pre-existing flaws made the initiation irrelevant, in my
opinion. I would go farther and argue that essentially all fatigue
failures of bike components are initiated at geometric stress
concentrations or mechanical damage sites. I should also probably
include microstructural perturbations like heat affected zones from welding
or brazing.
> just so you know, i /have/ straightened an xtr crank. with apparent
> success. it's in weekly use by a friend and has been for the 2 years
> since we worked on it. i take care to check it each time i see it,
> but so far, so good. ymmv.
>
Well,that is an interesting data point. Too bad that we did not hear
that earlier. In a forum where we do not really know the
qualifications of the participants, I generally draw conclusions based
on the collective individual experiences (like this one) and what I
know from my technical background. I like to think that I can also
be swayed by a good technical argument.
>
> if someone writes into an open forum and starts dispensing "advice"
> based on incorrect or incomplete data, then i don't see how they can
> possibly expect to have a problem [assuming their ego allows] if
> someone knows different. if you think i'm wrong, go ahead and say so
> - just as long as you can to back it up. just don't expect bluster to
> be an effective smokescreen that's all.
>
So based on your knowledge and experience you would recommend to
someone in this forum that they straighten a bent crank? I would not.
My experience has left me much less sure that I know the safety
envelope.
>
> i chose my pc analogy carefully. the bike shop solution is to replace
> the piece. it's quick, simple, and you can feel safe in the knowledge
> that all the other bike shops will say the same thing - just go ahead
> & reinstall windows.
I understood your analogy. I offer this one: If your system has been
compromised by a hacker, would you trust that system with data that
your company depends on or would you reinstall the operating system?
I suppose that if you know as much about windows as you do aluminum
alloys you would patch the registry, manually clean the system and
move on, or whatever. I run and administer various unix systems
myself, but would not trust a compromised sytem, because I don't
believe that I can know for sure that there is no malicious code
planted somewhere. (OK, I should run a file modification monitor of
some kind, but I do not know of a metallurgical equivalent.)
>
> /but/, if you can use the registry editor, or you know something like
> "fdisk /mbr", i personally think it's worth exploring those options
> before using the "one size fits all" remedy. but hey, i'm the guy
> that fixed my car for the cost of a $15 relay when the dealer wanted
> $2,300 to replace the ecu & ignition system.
So you are not only an uber-metallurgist, but a computer guru and auto
mechanic. There are at least a few regular posters here with a lot of
technical and engineering expertise, along with several bike shop
owners who have a large amount of empirical data available. I also
consider myself to be well rounded technically, but I am not going to
get into "my Dad can beat yours" in this forum. My point is that the
various people that are recommending replacement are not necessarily
doing that just because that is all that they are capable of
understanding.
I am sure that this has become very boring to most of the potential
audience, so I suggest that you contact me by e-mail if you want to
continue this. If you want the last word in this thread, have at it.
Dave Korzekwa
Ted Bennett
> afaik, 7400 series cranks are dural - forged & precipitation hardened.
> and as a metallurgist, /you/ should be able to get a very good feel for
> it's processing history just by looking. my old prof used to throw us
> pieces of planes and have us tell him what it's [sic] processing history was
> just by looking - even if we didn't know what the part was! if it's
> machined, you know part of it's history. if it's forged, you know part
> of it's [sic] history. if you look on shimano's web site, you know part of
> it's [sic] history - or at least enough to make judgement based on your
> experience of the available options!!!
Jim, in the interest of clarity, would you please learn the difference
between "its" and "it's". It makes a big difference in the meaning.
But please continue posting, your expertise is valuable here.
--
Ted Bennett
Portland OR
jim beam
> designation?
no. shimano's site gives this info:
http://bike.shimano.com/Road/Dura-Ace/componenttemplate.asp?partnumber=FC-7701
that's for 7700 series not 7400, but i believe the only real difference
is the "hollowtech" fabrication route.
> If you can infer the
> alloy and heat treatment by looking at a piece
not exactly, but there are a limited number of routes to making
component for kind of application and you can therefore take an educated
guess.
> So based on your knowledge and experience you would recommend to
> someone in this forum that they straighten a bent crank? I would not.
> My experience has left me much less sure that I know the safety
> envelope.
you definitely have a good and valid point. all i'm saying is that for
the situation as described, i would be inclined to give straightening a
go. judging by the way jan has described his concerns, the quality of
the piece, the extent of the deformation and the fact that he's alert to
the dangers of surface defects, i think he's a good candidate to conduct
the experiment he seems to want to undertake. particularly as a
replacement for this extinct product line is no longer available. i do
*not* however think that all bent cranks are candidates for
straightening and i'm saying this to jan, not anyone else. i guess i
need to be more specific in making this statement.
> If your system has been
> compromised by a hacker, would you trust that system with data that
> your company depends on or would you reinstall the operating system?
no, in that situation, i'd wipe, just like you. but if i had a problem
with lilo.conf [or some such] i'd edit it to get the system back on its
feet rather than reinstall. the right solution for the problem.
> My point is that the
> various people that are recommending replacement are not necessarily
> doing that just because that is all that they are capable of
> understanding.
any implication to that effect was not intended. i'm merely saying that
/i/ think there's more than one solution to the problem and that thought
is required in each case.
j
Jan Pinkowish
> > Don't do it. It doesn't like being bent once, let alone twice...
> is not all focussed on a weak spot like the spindle or pedal holes.
> you are absolutely right in that the /ideal/ solution is to buy new &
> start again, particularly if you don't have the skill or experience to
> the material's limits, there's no reason not to give it a go. i would
> /not/ say this for anything other than high end components like the xtr
> mentioned here.
The crank is a 7400 series Dura Ace. It has a rectangular profile.
The crank was bent when a car hit my foot, and my leg, and my thigh. So,
it was a cushioned impact.
Of course I'm not being being sensible. I'm an MIT grad which means I
know just enough about lots of things to get myself in trouble.
My thinking is to secure the BB end of the crank, wrap the straight
section in a cloth, and use a steel tube(ideally with a flat profile) to
lever the arm at intervals(pick a distance--10mm, 15mm?). Assuming the
straight section of the arm is 130mm, that means about a dozen
micro-tweeks. I've got a microscope, so I can check before and after.
I won't need the titanium cup that Sheldon suggests. I already have one
of his concrete saddles.
Jan
--
Scic
>My thinking is to secure the BB end of the crank, wrap the straight
>section in a cloth, and use a steel tube...
As long as you're going to do it, why not just place it between the jaws of a
good machinist's bench vise and tighten. Wood lath can be used on either side
to protect the finish.
Just an idea, and not a very good one. I don't think I'd attempt to straighten
one if bent.
Sig
Chicago
Werehatrack
have said:
>The news is full of these enhanced words, roadway instead of road,
>weather system in place of weather, heavy traffic conditions instead
>of heavy traffic, rain showers instead of showers...
Unlike for French, there is no sanctioning body to declare what is and
is not part of the English language, or what any given word's precise
meaning may currently be; indeed, the OED's compilers have expressly
stated that they only catalog, not dictate, the usages of the words as
they are found in the language.
BTW, "cog" as an abbreviation of "cogwheel" has been in common usage
in machinery manuals and documentation for at least 30 to 40 years;
I've been seeing it for at least that long. Yes, technically, the
original usage of "cog" limits that word's applicaility to the actual,
individual (and separable!) tooth...but the usage has long since moved
on. In my experience, old "cog" = new "tooth", old "cog-wheel" = new
"cog" in common usage. Most of this is probably due to the fact that
unlike those produced by19th-century techniques, virtually all modern
toothed wheels are made by machining metal away from a solid blank to
produce integral teeth, rather than taking a wheel, perforating it,
and inserting teeth. As such, the old sense of "cog" doesn't really
apply to the modern product at all.
But I agree that a lot of the needless added complication of
terminology (particulatly the gratuitous "ness") is aggravating when
it adds nothing to the precision of the expression. (However, the
*simplification* implicit in the shift from "cogwheel" to "cog" would
seem to be a move in the opposite direction...)
(OTOH, "weather" is what's happening to me, but a "weather system" is
what's bringing those local effects to my area. Not all added
verbiage is superfluous.)
On the poster's original topic, though, I'd be happier if the crank
was straightened using a press, but that's because I've always tended
to use presses to straighten things. It could also be done with care
using a large vise and three soft support blocks...if the aluminum
hasn't become work-hardened in the area of the bend. (If it has, it
may still be possible to render it *useful*, but it may not be
possible to return it to it's exact original shape.)
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