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.