On 30 Sep, 13:55, jim beam wrote:
On 09/29/2009 10:01 PM, wrote:



On Sep 29, 6:52 am, *wrote:
On Sep 29, 12:37 am, wrote:

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. I am
glad you escaped any mishap.

It doesn't have anything to do with rust or cleanliness.
There is a bit of surface oxidation inside the fork,
but it's totally superficial.

There is a stress concentration where the fork
crown meets the blade. *The joint was possibly
overheated during manufacture leading to a
weakness at the braze. *The crack initiated at
the rear of the fork, at the place where the crown
meets the blade, and propagated forward.

You can kind of see this from the pictures

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

Along the broken surface, at the upper right it's
fairly dark, which indicates it's been cracked
for a while and exposed to atmosphere, dirt etc.
This is where the crack follows the line of the crown.
Along the front of the fork blade, the line of breakage
is more smooth than scalloped, as if it were just
torn away, and the surface looks cleaner. *This is
what was still attached until the final break
happened.

disagree - this is not a typical fatigue fracture. *the fact that part
of the crown has come away with the blade is testament to that - highly
unusual.

more likely is a combination of poor brazing leaving a gap between the
crown and the blade. *subsequent chroming would leave chromic acid
deposits [and others] which would partially erode both the blade and the
crown, and initiate fatigue. *the rest is simply fatigue propagation.

I have made this kind of fracture at thre other end of the forks when
attempting to correct a build error. You know, cold set the forks.
New fork blades ,I was bending them but they wouldn't give, used
alittle more leverage than I expected and they snapped. Checked with
my trusted framebuilder, and he said "Nio, they shouldn't have done
that. You just cold set the forks after brazing." The coarse
granularity of what was steel was caused by an excess of spelter being
absorbed due to prolonged and/or excessive heat. There was no chrome,
only paint. The 'steel' failed in tension with two applications of
force. The point is the metal would not yield, it could only
fracture. The klutz who had 'brazed' the forks had turned the
advanced steel into a similar metal to cast iron. Only the colour of
fracture was different. This had the slightest tinge of yellow where
one would expect blue or neutral. Cast iron is grey with variations
of shade in the granulation.