Robert Kercher wrote, On 7/17/2007 11:54 AM:
>> I recently dismantled a Shimano cassette that was held together not
>> by rivets but by small bolts. They were all loose and the cassette was
>> a lot tighter after I cinched them up a little.
>>
>>
>>
>> Keith
>>
> I don't know how common the bolts are, but they are very useful for
> recycling the riveted cassettes. Just grind away head of the rivet and
> recycle the useable gears with the bolts plus the smallest gear from the
> bolted cassette (which is the one with the thread for the bolts).
>
> My guess is that Shimano went for the rivets because
>
> a) they are cheaper
>
> b) it makes reusing good gears of cassettes more difficult
>
> Somebody please contradict me. I also would like to know why Shimano
> went from regular grooves for cassettes which enable me to turn the
> gear by 180 degrees, thus doubling its service life to an irregular
> pattern which prevents this. Why do I sense the evil monopoly here?
>
> Sigh. If economy would only be ruled by engineers and not marketing
> people....
>
> Robert
Shimano's engineers would point out to everyone that their Hyperglide
sprockets are specially designed so that that the chain will to engage
two adjacent sprockets simultaneously during shifting. Shimano shapes
each of their sprocket with a set of ramps and modified teeth that
allows the chain to mesh with the new sprocket before it has disengaged
from the old one. This system provides much smoother shifting than older
designs. But it also means that each sprocket must be oriented so that
the "take-off teeth" on one sprocket lines up with the "landing teeth"
on the next sprocket. Flipping a sprocket 180 degrees "to double its
service life" would upset this geometry and probably result in a
cassette that would be very difficult to shift. So all Hyperglide
sprockets have a special spline to ensure that they can only go one one way.
It seems like a reasonable engineering trade off - better shifting
performance verses somewhat reduced servicability.
See:
http://sheldonbrown.com/gloss_ho-z.html#hyperglide
http://sheldonbrown.com/k7.html
--
Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)