Fw: bore distance: was Re: hammer replacement

[David Love]

In a class given by Richard Davenport he demonstrated that over centering 
the hammer by 2 mm resulted in a reduced DW of 4 grams and an increased UW 
of 1 gram.  The balance weight is reduced by 2.5g as is the friction.  Let's 
assume this is true.  Of additional interest to me is this:  The change in 
downweight is measured from the rest position.  But the downweight can be 
measured from any point in the stroke.  If you measure the downweight from a 
point, say, when the hammer is halfway to the string, you will get a reading 
that is something less than the downweight measured from rest position.  But 
the downweight measured from the halfway point should not vary as much 
between the over centered and normally centered hammers.  If we hypothesize, 
for the moment, that measured starting from the halfway point, the 
downweights are equal.  Then in the normally centered hammer there would be 
a 4 grams greater difference between the downweight measured at rest and the 
downweight measured halfway through the stroke.  Another way of saying it is 
that the rate of change of resistance through the key stroke would be 
greater in the normally centered hammer than in the overcentered hammer.  If 
that is true, it suggests to me that the overcentered hammer would have a 
"smoother" feel.  The key would not feel as though it is falling away from 
you once you got it moving or that the resistance goes through a more sudden 
change.

On another matter, the loss of power from an overcentered hammer I believe 
comes from the hammer delivering a glancing blow to the string (if it is not 
perpendicular on contact).  Raking the hammer out should solve that problem.

David Love

>From: Newton Hunt <nhunt@optonline.net>
>Reply-To: pianotech@ptg.org
>To: pianotech@ptg.org
>Subject: Re: Fw: bore distance: was Re: hammer replacement
>Date: Sat, 30 Jun 2001 07:26:25 -0400
>
>This discussion on hammer bores is great.  Now we need some numbers so we 
>can
>specify what we want and how any changes will effect action performance.
>
>This is exciting stuff.
>
>More, more!
>
>		Newton

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