Capstans... which brings me back to....

[David Ilvedson]

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Ric,

You've really blown it.  You now cannot take out a patent on your=
 idea...;-]  

"if you publish a method before patent filing, novelty is=
 violated and you 
can get no patent"  Bernie

Or maybe this isn't considered publishing?

David I.







Original message
From: Ric Brekne 
To: pianotech 
Received: Sun, 17 Apr 2005 22:26:26 +0100
Subject: Capstans... which brings me back to....


And update on my Magnetic Assist mechanism for the grand action.=
 The Virtual capstan of a couple years back that btw has been  up=
 and working just dandily this past year now.  8 hours a day they=
 are banging away on this instrument..

But too the point.... I have not been satisfied trying to deal=
 with the standard capstan adjustment when using the fold down=
 magnet assembly.   So... I've come up with a new version of the=
 old rocker arm... which I think has many good points.

Note... The following  amounts to Public Disclosure of an=
 invention. True to style any one is free to open source develope=
 the concept as they wish, but no patents can follow unless one=
 devises a clear improvement on the basic idea.

First a drawing of the rocker arm.



The assembly features an axled roller (brass) instead of a=
 standard capstan for the interface with the whippen cushion. It=
 is also axled to the key (red dot on the half round in the=
 middle) The magned assembly is just behind that, and the height=
 adjustment is in the front.  It employs a lock nut on both the=
 under and top sides of the rocker arm.  This allows for precise=
 adjusment of the roller height with the use of only one screw=
 instead of the old two screw type. Further, only one screw is=
 needed as the assembly is held in place both by the front=
 adjustment screw and the center pinnning in the middle.

All this allows for complete freedom of adjustment of both  the =
 physical <<capstan>> height (in the form of the roller) and the=
 virtual capstan height (magnet)

The roller allows for a minumum of friction between the key=
 assembly and whippen cushion. No sliding whatsoever.

An article on this is in the works and I expect to publish soon.=
 The Magnetic Assist Grand Action by Richard Brekne is an open=
 source development project and can be used to replace=
 significant amounts of lead in the keys.  Read the article in=
 both the PTG Journal last year and the European for more=
 infomation.

Cheers 
Richard Brekne



A common misperception.  It does slide.  The involute curve is=
 the standard
gear tooth profile.  The important quality of the involute curve,=
 is that
it transmits uniform angular velocity.  So that as the driving=
 gear rotates
at constant RPM, the driven gear also rotates at constant RPM,=
 with minimum
noise and vibration.  But they do slide.  Make your self a paper=
 cutout and
try it.

It's also interesting to consider the angle of gear teeth. =
 Standard angles
for spur gears are 14 and 20 degrees.  14 degree teeth are=
 smoother and
quieter, and have a longer wear life because at a given load they=
 have
lower contact stress.  In fact, zero angle or negative angle=
 would be even
better, from a contact stress point of view, but with small or=
 negative
angles there is a geometry problem known as "undercutting", =
 where the base
of the tooth ends up narrower than the contact area, and is prone=
 to
fracture.  20 degree teeth are a compromise, used for pinions=
 with very few
teeth to prevent undercutting.

So does a capstain slide on the wippen cushion felt, except for=
 the instant
that the contact point passes through the "magic line".  Before=
 and afer
that point, the Overs capstain slides the least, standard=
 vertical capstan
slides a little more, and the Steinway backwards leaning capstan=
 slides a
little more than that.

more than you wanted to know, and it still does not explain why=
 S&S might
have done that.

Mike


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