Jim Beam writes:
>> It probably has carbon-steel spokes, as did most bikes back then. Although carbon-steel spokes
>> are not as strong as stainless (and prone to rusting) they are less subject to fatigue than
>> stainless spokes are.
> The carbon alloy steel spokes were galvanized most likely. Flashy [literally] ones were
> chrome plated.
> Technically, carbon alloy steel wire is usually stronger than stainless. It's still used in steel
> rope where strength [&/or price] outweighs weather considerations.
If exposed to weather, such cables are galvanized and often painted to protect them from rusting.
This is mostly a matter of cost, stainless cables being far more expensive than carbon steel.
> Carbon steel spokes /were/ less prone to fatigue. Modern stainless steels are significantly better
> than they used to be and now the two are roughly comparable. High strength carbon alloy steels do
> not typically have a fatigue endurance limit - it's just that it's been possible to make "cleaner"
> carbon alloy steels [cheaper] longer than has been possible for stainless.
> If ever you travel to San Francisco, there are two pieces of interesting wire that you must see:
> One is at the golden gate bridge. There is a section of the main span rope cut open for inspection
> at the visitor center. Interesting un-twisted strand design. High strength carbon alloy steel.
You will notice that these "cables" are completely encased in a waterproof steel jacket and are in
real life pumped solidly full of grease like preservative... as they are on most suspension bridges.
The suspenders on the GG Bridge are exposed strands but are helically wound and are galvanized and
painted with the traditional red paint of that bridge. What is less evident to the casual observer
is that because the bridge lives in fog and salt spray, it does not have exposed riveted lattice-
work as other bridges around the bay. It's towers are enclosed so the structural elements within the
towers can be kept dry and clean.
> The other is the crowd barrier rope at the cable car turnaround on Powell & Market. It's a piece
> of actual cable car traction rope. Unlike all the [wire] rope you normally see that is twisted to
> make the exterior strands run axially, this one is twisted to make the exterior stranding as close
> to perpendicular as possible. This is to give maximum possible friction for the cable car's rope
> clutching mechanism as it goes up the hills. Again, carbon alloy steel.
Since these cables bend around pulleys and curves, they must be helically wound or they would break
immediately. They are made this way for the same reason control cables on bicycles are helically
wound... so they will have uniform stress in all strands when bending around curves. Cable car cable
has a special layer of external friction strands that are smooth and rectangular, like the ones for
aerial trams where cables are sued as rails on which the tram rides. This is done to reduce wear
that would occur if the outer strands had a round cross section or even themselves made of strands,
as are old Campagnolo bar-end shift cables.
> /utterly/ useless trivia, but thrillingly geeky!
http://www.cablecarmuseum.com/Anat/Anat.html
Don't pass along myth and lore.
Jobst Brandt
[email protected]
