On Sat, Feb 14, 2015 at 10:34 PM, Benedikt <neutralbuoya...@comcast.net> wrote:
> I added a few pictures for those of you who wanted to see the other side > of the crank including some "mating" the two up. > > https://www.flickr.com/photos/neutralbuoyancy/16529273621/in/album-72157607896493013/ > - Brian > > Thanks, that was very helpful. It didn't look like I thought it would at all, judging from the first photos - I thought the big gentle inner curve was a flat machined surface. Even if there's a gentle curve, the very transition to the arm is abrupt and sharp, and it's a definitive stress riser. And the crack started exactly there. Even so, I would not say it's a poor design - it could improve in that detail to have more margin of error, but it's likely a materials problem in manufacturing. I have decades of experience with dogsled runners made of 7075 aluminium, and they are subject to an extreme amount of flex and corrosion compared to a bicycle crank, and they mostly break because of severe mechanical damages and cut-outs that initiates the break. I don't know how the original French cranks were shaped there, I use an old Stronglight 49A crank myself daily in summertime but the bike is in storage now and I can't take a look. Johan Larsson, Sweden -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
