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Broken steel road bike fork



 
 
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  #11  
Old September 29th 09, 10:00 PM posted to rec.bicycles.tech
someone
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Default Broken steel road bike fork

On 29 Sep, 16:29, Tim McNamara wrote:

Chrome plating *can* result in embrittlement but does not necessarily do
so. *Millions of bikes and other load bearing appplications are chromed
without such failures happening.


More likely the cause of embrittlement is what causes it with non-
chromed forks. Overbrazed.

Current common practice is to use oxy-acetylene torch and spelter wire
because it is quicker overall. I suspect the higher temperatures
obtainable with oxy-acet ensure a deeper penetration of the spelter,
alloying with the steel, causing the embrittlement. In skilled
experienced hands, oxy-acet does produce excellent results when there
are no distractions. I would certainly favour a builder which had the
certification of qualification from a technical college in the use of
oxy-acetylene for brazing if I was unable to locate one with historic
recommendation. That (college cetificate) does not necessarily
qualify him to braze cycle forks. And be careful that builders
although say they do the work, leave spotty Nigel to do the
preperation.

Hearth brazed forks heated with natural gas may also suffer with
brass embrittlement due to excessive duration in the flame. Good
preparation is the key. No cutting with abrasive grit, only by file,
plenty of flux in the joint and the use of granular spelter inside the
end of the fork reduce the heat exposure of the steel so keeping the
alloying depth to a minimum at the edge of the crown. I think it be
the filling from the end of the crown rather the end of the fork to be
the killer.

Nigel, may of course used carbarundum instead of the file and scraper
to prepare the forks and crown and if he's applied a paste flux, how
much water?


The reason for the failure seem pretty self-evident in the photo. *Note
how the crack followed the shore line of the socket so perfectly, and
note the relative thicknesses of the metal. *Note also the lack on a
reinforcement tang on the inside of the fork leg.


Overbrazed.


for the future, consider quality cfrp - unless abused, it's pretty
much "fatigue proof".


More clueless advice from "jim beam."


overbrazed.
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  #12  
Old September 29th 09, 10:15 PM posted to rec.bicycles.tech
someone
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Posts: 2,340
Default Broken steel road bike fork

On 29 Sep, 21:12, Jobst Brandt wrote:
Frank Krygowski wrote:
When I took the wheel off, my heart skipped a beat. *Without much
effort, this is the result:


*http://www.bitrealm.com/misc/fork/p1000783.jpg
*http://www.bitrealm.com/misc/fork/p1000784.jpg
*http://www.bitrealm.com/misc/fork/p1000785.jpg



It was hanging by no more than 2mm of steel. *I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. *I don't think it would have held together and
when you lose the front like this, it's going to be bad.

Lucky you caught it when you did. *Last year, our old custom tandem
let go of both blades simultaneously. *The warnings I got were
nowhere near as explicit as yours. *Fortunately, we were moving only
about 10 mph at the time.
In my case, the bike was built by Jim Bradford, formerly of the
Atlanta, Georgia area. *It was the last bike he built before getting
married and leaving on a honeymoon. *I suspect he slapped in
whatever fork blades he had lying around in order to get the job
done, because the wall thickness was roughly one-third of the proper
gage for Reynolds 531 tandem forks.
I wish I could offer advice on how to choose a competent and ethical
frame builder, but I can't.
BTW, I think you shouldn't have too much trouble finding a
replacement. *I was able to buy a replacement tandem fork from
Tandems Ltd in Alabama. *For a single bike I intend to build, just
last year I was able to buy a chromed Japanese fork from Citybikes
in Portland, Oregon.


*http://www.citybikes.coop/

This is a classic fork failure in which the lug interface between fork
blade and fork crown had not been feathered after brazing. *This
failure could be seen coming while "Cinelli" fork crowns that are
internally lugged, do not reveal their trend to failure until after
fracture. *However after failure they were obvious failure points.

Many joints between lugs and frame tubes may be shiny chrome but they
have discontinuous transitions that cause fracture as in this one.

Jobst Brandt


you're as bad as beam. The error is in the brazing. Plenty of aero
crowns and forks survive despite their 'design flaw'.

I used a 'full aero' crown on a Raleigh Competition for five years
with 531 light gauge forks with no ill effects. I repainted the frame
and forks in the last year and so know, because I gave it a careful
inspection, that there were no faults whatsoever in the
framebuilding. There did not appear to be any dressing of the lugs
following brazing, the cutouts were clear and the depth was consistent
all around with a tiny fillet. One 'fault', seat stay end cap had a
little gap in the braze, the gap was irrelevant and sealed by the
paint. The dent I put in the seat stay (crash) could not be covered
by paint.
  #13  
Old September 29th 09, 10:34 PM posted to rec.bicycles.tech
jay
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Posts: 117
Default Broken steel road bike fork

On Sep 29, 1:12*pm, Jobst Brandt wrote:
Frank Krygowski wrote:
When I took the wheel off, my heart skipped a beat. *Without much
effort, this is the result:


*http://www.bitrealm.com/misc/fork/p1000783.jpg
*http://www.bitrealm.com/misc/fork/p1000784.jpg
*http://www.bitrealm.com/misc/fork/p1000785.jpg





It was hanging by no more than 2mm of steel. *I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. *I don't think it would have held together and
when you lose the front like this, it's going to be bad.

Lucky you caught it when you did. *Last year, our old custom tandem
let go of both blades simultaneously. *The warnings I got were
nowhere near as explicit as yours. *Fortunately, we were moving only
about 10 mph at the time.
In my case, the bike was built by Jim Bradford, formerly of the
Atlanta, Georgia area. *It was the last bike he built before getting
married and leaving on a honeymoon. *I suspect he slapped in
whatever fork blades he had lying around in order to get the job
done, because the wall thickness was roughly one-third of the proper
gage for Reynolds 531 tandem forks.
I wish I could offer advice on how to choose a competent and ethical
frame builder, but I can't.
BTW, I think you shouldn't have too much trouble finding a
replacement. *I was able to buy a replacement tandem fork from
Tandems Ltd in Alabama. *For a single bike I intend to build, just
last year I was able to buy a chromed Japanese fork from Citybikes
in Portland, Oregon.


*http://www.citybikes.coop/

This is a classic fork failure in which the lug interface between fork
blade and fork crown had not been feathered after brazing. *This
failure could be seen coming while "Cinelli" fork crowns that are
internally lugged, do not reveal their trend to failure until after
fracture. *However after failure they were obvious failure points.

Many joints between lugs and frame tubes may be shiny chrome but they
have discontinuous transitions that cause fracture as in this one.

Jobst Brandt- Hide quoted text -

- Show quoted text -



What is feathering?
  #14  
Old September 29th 09, 10:48 PM posted to rec.bicycles.tech
someone
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Posts: 2,340
Default Broken steel road bike fork

On 29 Sep, 22:34, jay wrote:
On Sep 29, 1:12*pm, Jobst Brandt wrote:



Frank Krygowski wrote:
When I took the wheel off, my heart skipped a beat. *Without much
effort, this is the result:


*http://www.bitrealm.com/misc/fork/p1000783.jpg
*http://www.bitrealm.com/misc/fork/p1000784.jpg
*http://www.bitrealm.com/misc/fork/p1000785.jpg


It was hanging by no more than 2mm of steel. *I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. *I don't think it would have held together and
when you lose the front like this, it's going to be bad.
Lucky you caught it when you did. *Last year, our old custom tandem
let go of both blades simultaneously. *The warnings I got were
nowhere near as explicit as yours. *Fortunately, we were moving only
about 10 mph at the time.
In my case, the bike was built by Jim Bradford, formerly of the
Atlanta, Georgia area. *It was the last bike he built before getting
married and leaving on a honeymoon. *I suspect he slapped in
whatever fork blades he had lying around in order to get the job
done, because the wall thickness was roughly one-third of the proper
gage for Reynolds 531 tandem forks.
I wish I could offer advice on how to choose a competent and ethical
frame builder, but I can't.
BTW, I think you shouldn't have too much trouble finding a
replacement. *I was able to buy a replacement tandem fork from
Tandems Ltd in Alabama. *For a single bike I intend to build, just
last year I was able to buy a chromed Japanese fork from Citybikes
in Portland, Oregon.


*http://www.citybikes.coop/


This is a classic fork failure in which the lug interface between fork
blade and fork crown had not been feathered after brazing. *This
failure could be seen coming while "Cinelli" fork crowns that are
internally lugged, do not reveal their trend to failure until after
fracture. *However after failure they were obvious failure points.


Many joints between lugs and frame tubes may be shiny chrome but they
have discontinuous transitions that cause fracture as in this one.


Jobst Brandt- Hide quoted text -


- Show quoted text -


What is feathering?


JB flapping.
  #15  
Old September 30th 09, 12:59 AM posted to rec.bicycles.tech
someone
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Posts: 2,340
Default Broken steel road bike fork

On 29 Sep, 23:15, Jobst Brandt wrote:
Jay Drew wrote:
What is feathering?


A fading out of one cross section into another where they meet:

*http://www.gtgtandems.com/tech/brazing.html


like I said, JB flapping. That's about fillet joints not lugged, as
in the OP's photographs.


The sudden step in cross section causes a stress concentration that
leads to cracking.


No, you're flapping. and maybe you're cracking.

*Most better metal workers are aware of this.
Sadly the sloping fork crown of 1960's Cinellis were not feathered and
cracked for those of us who rode much.


Should have chosen a better metal worker, rather than one who would
fit such a terrible fork crown , and then overbraze it so you could
prove you rode much.

*After two of these failures I
got a Masi Fork crown instead. *




Feathering can be done as Hetchins did with curlicues and fade-outs,
or as Masi did with tapering pointed lugs.


The ovality of the fork blade spreads the strain so there is no
extraneous stress level.
  #16  
Old September 30th 09, 03:40 AM posted to rec.bicycles.tech
jim beam[_5_]
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Posts: 941
Default Broken steel road bike fork

On 09/29/2009 03:15 PM, Jobst Brandt wrote:
Jay Drew wrote:

What is feathering?


A fading out of one cross section into another where they meet:

http://www.gtgtandems.com/tech/brazing.html


wrong. feathering is simply filing the edges of the lug.



The sudden step in cross section causes a stress concentration that
leads to cracking.


which is why it's not a straight cross section, it's got curved features
that mitigate - effectively radius reduction, a standard fatigue
mitigation technique.


Most better metal workers are aware of this.
Sadly the sloping fork crown of 1960's Cinellis were not feathered and
cracked for those of us who rode much.


that's not feathering - that's radius reduction.


After two of these failures I
got a Masi Fork crown instead.


good for you. of course, if you'd understood what you were looking at
the first time, you'd only have suffered one failure...



Feathering can be done as Hetchins did with curlicues and fade-outs,
or as Masi did with tapering pointed lugs.


nope, that's radius reduction, not feathering. hetchins and masi [and
many others] do feather, but they do it with a file, and it's not a
function of lug shape.
  #17  
Old September 30th 09, 03:40 AM posted to rec.bicycles.tech
jim beam[_5_]
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Posts: 941
Default Broken steel road bike fork

On 09/29/2009 01:12 PM, Jobst Brandt wrote:
Frank Krygowski wrote:

When I took the wheel off, my heart skipped a beat. Without much
effort, this is the result:


http://www.bitrealm.com/misc/fork/p1000783.jpg
http://www.bitrealm.com/misc/fork/p1000784.jpg
http://www.bitrealm.com/misc/fork/p1000785.jpg

It was hanging by no more than 2mm of steel. I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. I don't think it would have held together and
when you lose the front like this, it's going to be bad.


Lucky you caught it when you did. Last year, our old custom tandem
let go of both blades simultaneously. The warnings I got were
nowhere near as explicit as yours. Fortunately, we were moving only
about 10 mph at the time.


In my case, the bike was built by Jim Bradford, formerly of the
Atlanta, Georgia area. It was the last bike he built before getting
married and leaving on a honeymoon. I suspect he slapped in
whatever fork blades he had lying around in order to get the job
done, because the wall thickness was roughly one-third of the proper
gage for Reynolds 531 tandem forks.


I wish I could offer advice on how to choose a competent and ethical
frame builder, but I can't.


BTW, I think you shouldn't have too much trouble finding a
replacement. I was able to buy a replacement tandem fork from
Tandems Ltd in Alabama. For a single bike I intend to build, just
last year I was able to buy a chromed Japanese fork from Citybikes
in Portland, Oregon.


http://www.citybikes.coop/

This is a classic fork failure in which the lug interface between fork
blade and fork crown had not been feathered after brazing.


no it isn't jobst.

1. you don't know **** about fatigue.
2. you've failed to observe the fatigue interface.
3. you don't understand the nature of the loading forces.
4. you're completely ignorant of the effects of chrome plating.


This
failure could be seen coming while "Cinelli" fork crowns that are
internally lugged, do not reveal their trend to failure until after
fracture. However after failure they were obvious failure points.


er, this is not a cinelli fork. and the failure is not the same.



Many joints between lugs and frame tubes may be shiny chrome but they
have discontinuous transitions that cause fracture as in this one.


no, they cause fatigue. fatigue causes fracture. what did you learn at
stanford jobst? analysis and logic were obviously absent from your
curriculum.


  #18  
Old September 30th 09, 03:42 AM posted to rec.bicycles.tech
jim beam[_5_]
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Posts: 941
Default Broken steel road bike fork

On 09/29/2009 08:29 AM, Tim McNamara wrote:
In article
,
wrote:

On Sep 29, 5:42�am, jim wrote:
On 09/28/2009 09:37 PM, wrote:

So, I've been noticing that the front brakes of my road bike were
acting "grabby" in that the front would shimmy pretty badly just
as I'm coming to a stop. �The rims felt a little sticky, maybe
some Gatorade got on them and it hasn't really rained in a while.
�I cleaned the wheels last night and rode into work today. �It
was still bad, but didn't seem as bad. This has been going on for
a week, I didn't think anything of it. �I decided to not ride
after work and just come home, coming down the driveway, the
grabby-ness was really pronounced, so I figure that the brake
pads must be contaminated with something. When I took the wheel
off, my heart skipped a beat. �Without much effort, this is the
result:

http://www.bitrealm.com/misc/fork/p1000783.jpg
http://www.bitrealm.com/misc/fork/p1000784.jpg
http://www.bitrealm.com/misc/fork/p1000785.jpg

It was hanging by no more than 2mm of steeel. �I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. �I don't think it would have held together
and when you lose the front like this, it's going to be bad.

The shimmy was the wheel moving back and forth due to the fork
leg being fatigued. �There hasn't been any accident damage since
I put this fork on the bike. �The crack was almost all the way
through, starting from the BACK of the fork leg.


The crack initiating in the back of the leg is not unusual.

chrome plate is bad for fatigue - it contains many fatigue
initiators.


Chrome plating *can* result in embrittlement but does not necessarily do
so. Millions of bikes and other load bearing appplications are chromed
without such failures happening.

The reason for the failure seem pretty self-evident in the photo. Note
how the crack followed the shore line of the socket so perfectly, and
note the relative thicknesses of the metal. Note also the lack on a
reinforcement tang on the inside of the fork leg.


oh, timmy the retard is now a fatigue expert!!! tell us timmy, which
end of the microscope did you cram up your ass when you learned all this
bull****?



for the future, consider quality cfrp - unless abused, it's pretty
much "fatigue proof".


More clueless advice from "jim beam."


which is the larger force timmy - 1600N or 5000N?



This fork was on the bike for about 8 years and had probably around
12K miles on it in that time.

I would like to find a 1" threaded replacement that has eyelets for
fenders, but they seem pretty thin on the ground. I can find the
exact same fork shown here (in black) that I could still buy. It was
a 200 mm steerer tube with 35mm of threading. Cut, it is 190mm with
25mm of threading. The one shown here was made for 27" wheels and I
just run long reach calipers. I had to have the crown race cut from
27 to 26.4mm.

If not, any 1" threadless forks with eyelets and room for fenders?


Harder to find these days since most aftermarket forks are aluminum or
CF, lack eyelets and are for 700C wheels (if the bike was made for 27"
wheels, going to a 700C fork will affect the geometry). But I would
think that any bike shop with a QBP account could order you a fork to
fit. Or you could have one made, but that would be expensive.


what ridiculous retardation.
  #19  
Old September 30th 09, 03:47 AM posted to rec.bicycles.tech
jim beam[_5_]
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Posts: 941
Default Broken steel road bike fork

On 09/29/2009 02:16 PM, Still Just Me! wrote:
On Tue, 29 Sep 2009 05:42:51 -0700, jim wrote:

for the future, consider quality cfrp - unless abused, it's pretty much
"fatigue proof".


The fact that it was steel and demonstrated fatigue instead of just
failing catastrophically (like crappy fiber does when it fails) is the
only thing that saved him.


er, so a failure is better than a non-failure??? because you're
confused between fatigue and over-load or abuse??? jeepers dude, you're
winning that stupidity contest again!



As always, your advice is useless.


no, i cast pearls before ignorant incapable swine.
  #20  
Old September 30th 09, 03:48 AM posted to rec.bicycles.tech
jim beam[_5_]
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Posts: 941
Default Broken steel road bike fork

On 09/29/2009 06:52 AM, raamman wrote:
On Sep 29, 12:37�am, wrote:
So, I've been noticing that the front brakes of my road bike
were acting "grabby" in that the front would shimmy pretty
badly just as I'm coming to a stop. �The rims felt a little
sticky, maybe some Gatorade got on them and it hasn't really
rained in a while. �I cleaned the wheels last night and rode
into work today. �It was still bad, but didn't seem as bad.
This has been going on for a week, I didn't think anything of
it. �I decided to not ride after work and just come home, coming
down the driveway, the grabby-ness was really pronounced, so
I figure that the brake pads must be contaminated with something.
When I took the wheel off, my heart skipped a beat. �Without much
effort, this is the result:

http://www.bitrealm.com/misc/fork/p1...k/p1000785.jpg

It was hanging by no more than 2mm of steeel. �I shudder when I
think of the roads I was about to go on, including one really
bad bump at the bottom. �I don't think it would have held together
and when you lose the front like this, it's going to be bad.

The shimmy was the wheel moving back and forth due to the fork
leg being fatigued. �There hasn't been any accident damage since
I put this fork on the bike. �The crack was almost all the way
through, starting from the BACK of the fork leg.


well, there you go, "steel is real" has been the mantra- but the
phrase " suseptable to rust" could be added. The fork looks very
clean, so I wonder how it happened to escape your notice earlier.


no ****.


I am
glad you escaped any mishap.


 




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