From: Bernd.Kischnick@launchpad.unc.edu (Bernd Kischnick)
Subject: Re: Chain Maintenance Question
Summary: correct me if I'm wrong 
Keywords: chain wear hole
Organization: University of North Carolina Extended Bulletin Board Service
Date: Fri, 18 Dec 1992 17:50:30 GMT

In article <1460043@hplred.HPL.HP.COM> jbrandt@hplred.HPL.HP.COM (Jobst Brandt) writes:
>Bernd Kischnick writes:
>> [about Rohloff chains]
>
>All this [...] is speculation.  Let's cut out the pretentious jargon.

English is a foreign language to me, so I'll best pretend  that I don't
know the meaning of "pretentious", and apologize for any kind of
jargon my humble attempts in scientific English may resemble.

>Chains are a relatively well understood mechanical element and the
>machine industry has been using them for a century. [...]

Bicycle chains for use with derrailleurs, on the other hand, were not
invented before about 1930, because they obviously violate the fundamental
engineering dogma for chains, which demands that chain ring and
sprocket would absolutely definitely precisely have to be in line. This
indicates that industrial experiences are of limited helpfulness, and
explains why bicycle chains have not participated in the progress of
motorcycle o-ring chains.

>I don't believe for a minute that Rohloff bores non round holes in
>his components nor that he has oriented cam ground pins.

I don't know about those pins. Anyway, we cannot argue about facts. Either
the holes are slightly egg-shaped or they are not. Put a side
plate under your Tastschnittgeraet and check it, if you don't
believe it. As the holes are not drilled into the plates, it is not difficult
to change their shape.

>Normal elasticity of steel serves for adequate bearing contact and most
>liquid chain lubricants furnish an adequate separation between the
>rotating elements.  The grit is the undoing of all this and to
>claim otherwise is deception. 

I have intentionally left out those details of my simplified description,
because they do not really matter. Let me demonstrate this with an
everyday example:

What is the point in using pointed drills for drilling holes?
If I were to follow Jobst Brandt,  I could as well use a dull drill ---
which like the egg-shaped holes provides a larger contact area --- and
still do the same damage to the surface I want to pierce. The result of a
comparison dull vs. sharp drill does not change if I apply grit and grease
to the contact spot, only the total amount of destruction. q.e.d.

I refered to good old Coulomb and said that the total amount of friction
does not change. You want details: Because the larger contact area reduces
the fraction of abrasive friction, and because abrasive friction is more
lossy, the chain in fact is more effective. But this effect is of course
negligible.

>Of course you can do worse as in the
>case of the design introduced by Sedis.

It shifts slightly better, it is more silent, it is cheaper than a chain
with cylinders between the inner plates. Just my experience of course.

I don't like to have to defend that Rohloff chain which I have not yet
tested thoroughly in praxi. So I'd like to concentrate on the question
whether the design makes sense, and not whether Rohloff only claims to
implement it.

Finally, merry.christmas for all of you in net.world!
-   Bernd.

home address bernd.kischnik@cdc2.ifum.maschinenbau.uni-hannover.dbp.de
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