"Modern crank manufacturers also seem to not be aware that their name embossed into the metal is enough to start cracking."
More likely it is that they do know - they just want their name on the crank regardless.
=8-)
Robert Shackelford San Jose, CA USA
Quoting Eric Keller <eekeller@psu.edu>:
> I've seen pictures of pedal end cracks on modern cranks. One source
> of cracks is those scratches from toe clip straps that are prominently
> evident on your Stronglights. Modern crank manufacturers also seem to
> not be aware that their name embossed into the metal is enough to
> start cracking. I also have seen pictures of a TA crank that
> apparently came from a milling mark that would normally be hidden
> under the TA sticker.
>
> I can't really argue with your analysis, but I think it may just be a
> case of a surface wear mark being in the wrong place. In my work I
> have created hundreds of fatigue cracks. During the initiation phase
> there are many cracks that can get fairly large until one crack face
> wins out. Depends on the alloy as to how pronounced this might be.
> It can be amazing and disheartening how small of a flaw will cause a
> crack to start even when there is a much larger flaw nearby.
> Eric Keller
> Boalsburg, Pennsylvania USA
>
> On Mon, Jan 3, 2011 at 8:15 PM, verktyg <verktyg@aol.com> wrote:
> > This weekend I was assembling another French bike from the frame on up. I
> > had a set of Stronglight 105 cranks that I wanted to use on it. While
> > cleaning the left arm I noticed a small spot of dirt that wouldn't clean
> up.
> >
> > On closer examination it looked like a crack was starting so I examined
> the
> > arm under my 10x-60x-200x digital microscope. The crack was easy to see at
> > 10x and 60x it looked like the Nile River Delta!
> >
> > The crack is at the pedal end of the forged in flute.
> >
> > http://tinyurl.com/
> >
> > There's one picture that I drew in a red line to show that the crack is
> not
> > only across the arm at 90° but there is some laminar failure under the
> > surface to.
> >
> > What I suspect is that the billet may not have been hot enough when the
> > flute was hammered in and/or there was a lap seam flaw in the aluminum
> > billet.
> >
> > (LAP A surface irregularity appearing as a fissure or opening caused by
> > the folding over of hot metal fins or sharp corners and by subsequent
> > rolling or forging (but not welding) of these into the surface.)
> >
> > This makes 2 orphan Stronglight 105 RH crankarms... ;-(
> >
> > Stronglight produced the 105 crank arms with the forged in logo from
> around
> > 1875 until about 1980, After that they switched to a shallower flute (see
> > last picture).
> >
> > That's around the same area I've seen a number of Campy cranks crack. In
> the
> > early 80s most crank makers switched to flat top or slightly curved top
> > crank arms. I've not seen a pedal end crack like this one on any of the
> > latter style cranks.
> >
> > So, another suggestion for those long winter nights, closely examine your
> > crankarms for any signs of cracks developing.
> >
> > Good riding...
> >
> > Chas. Colerich
> > Oakland, CA USA