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Chain stay bridge musings

Old 08-13-22, 11:29 PM
  #26  
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Originally Posted by smd4 View Post
Not worried. My Cinelli doesn’t have a CS bridge, as I noted in the first post. But thanks for the suggestions.
Both my Cinellis do. But then, they are both old (mid-1960s), they both have long chain stays by today's standards, and both include an M5-threaded hole for attaching fenders. (Both of them also have one on the underside of the rear brake bridge,)

Other than for attaching fenders, does CS bridge vs. no brake bridge matter? Probably not at all, and certainly not a lot. My take: either way, if it was good enough for Cino and Luigi, it's good enough for me.
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Old 08-14-22, 05:47 AM
  #27  
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Originally Posted by davester View Post
If you're that worried about the extra weight, you could cut your shoelaces shorter or not take that last bite of sandwich at lunch.
I remember looking at photos of European pros in races back in the '60s and '70s and wondering why so many of them were wearing bulky-looking wristwatches. Your bike is as light as possible: why drag around the weight of that wristwatch when the guy holding the chalkboard (or whatever was) on the back of the motorcycle keeps showing you the time to the breakaway group?
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Old 08-14-22, 09:07 AM
  #28  
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Originally Posted by bikingshearer View Post
Other than for attaching fenders, does CS bridge vs. no brake bridge matter? Probably not at all, and certainly not a lot. My take: either way, if it was good enough for Cino and Luigi, it's good enough for me.
The absence of a chain stay bridge looks much more elegant to me. And it was good enough for Mario…
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Old 08-14-22, 09:54 AM
  #29  
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Originally Posted by smd4 View Post
The absence of a chain stay bridge looks much more elegant to me. And it was good enough for Mario…
"Less is more." I like it.

I've done a couple of chain and brake bridge repairs. Obviously a brake bridge is a necessity. Even if you're using cantilevers or brazed on centerpull posts it mitigates twisting of the small diameter seat stays when braking. @RustyJames brought this frame in to repair a brake bridge that was only held in place from one side.



Proud of my work, I posted it to a thread somewhere that I can't find. What I didn't notice, but @bulgie did was that the right side chainstay bridge didn't appear to be quite as attached to the stay as one would like. Sure enough, same issue. While heating the other side up to liquify the silver based filler I contemplated just leaving it off. I've always wondered what structural improvement it might give. I'm sure the extra triangulation stiffens the rear triangle a bit. Somebody with a finite element analysis (FEA) package could model this and answer that question, but this may well be a "yes, it does, but not significantly".

So, I still don't know if a chainstay bridge is worth brazing onto a frame, but I did learn that crowd sourcing quality control by posting pics to Flickr is a smart thing to do (thanks again, Mark B.!)
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Old 08-14-22, 10:31 AM
  #30  
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Originally Posted by gugie View Post
"Less is more." I like it.

I've done a couple of chain and brake bridge repairs. Obviously a brake bridge is a necessity. Even if you're using cantilevers or brazed on centerpull posts it mitigates twisting of the small diameter seat stays when braking. @RustyJames brought this frame in to repair a brake bridge that was only held in place from one side.



Proud of my work, I posted it to a thread somewhere that I can't find. What I didn't notice, but @bulgie did was that the right side chainstay bridge didn't appear to be quite as attached to the stay as one would like. Sure enough, same issue. While heating the other side up to liquify the silver based filler I contemplated just leaving it off. I've always wondered what structural improvement it might give. I'm sure the extra triangulation stiffens the rear triangle a bit. Somebody with a finite element analysis (FEA) package could model this and answer that question, but this may well be a "yes, it does, but not significantly".

So, I still don't know if a chainstay bridge is worth brazing onto a frame, but I did learn that crowd sourcing quality control by posting pics to Flickr is a smart thing to do (thanks again, Mark B.!)
A big thanks to bulgie for catching that separated stay.

Interesting discussion, this. I was rattle canning my fillet brazed SuperSport, looking at the integrated kickstand doodad and wondering if I could cut that off. I isn’t no genius regarding frame structural integrity so I left it in situ. Also, there’s something quaint about it that I like.
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Old 08-15-22, 07:48 PM
  #31  
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Originally Posted by 79pmooney View Post
West System. The issue I had was that the scrap was a roving-like material with plastic "threads" holding it together that did not break down like fiberglass mat when exposed to polyester resin. Also the roving-like coarse CF strands.

Carbon forks are vacuum bagged which squeezed the fabric against the fork mold; much like my inner tube wrap did manually. What CF forks don't get that my repair did was human eyes on the finished laminate. Flaws. little and big, are never seen until the fork breaks, is cut apart for forensics or is X-rayed or scanned. I could see all of my work after. Nothing hidden until 18 months later when I had the bike painted.
Vac bagging places 14.7PSI against the layup. More can be achieved with a two part mold. Think sheet molding compound in a press, with vacuum extraction.
Sonograms and infrared are the decent non destructive tests today.
Binding up the layup with innertube will improve the compaction, but nowhere near vacuum. Might get a nice surface between the binding laps.

I don't like all carbon forks. The industry has marketed the 1.125 to 1.5" tapered steerer as a stiffness thing, sure, but also reduces the deflection the carbon has to make at the crown race, that can be cheated by having the strands spiral at the turn vs meeting the corner head on.
The bike industry has jumped the shark in design there and the assembly schemes to route internal cables.
One brand has gone another way and placed the structural element of the fork IN FRONT of the frame headtube/steering axis. might be more aero to boot. first seen on TT machines, now on road bikes.
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