"Oval or Round Shanks" or to bend or not to bend

[pianoman]

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> From: Richard Moody  <remoody@easnetsd.com>
> To: pianotech@ptg.org
> Subject: Re: "Oval or Round Shanks" or to bend or not to bend
> Date: Thursday, September 04, 1997 12:48 AM
> 
> OK.   So has anyone seen rectangular hammmer shanks?  Well my
> Chickering Anniversery Grand has 'em. I better measure,  they might
> be square.  Hmm wonder if I can get replacements?
> 
> 	Also just to open another can of worms, what does "stiffness
> requirements of transferring the necessary energy to the hammer mass
> of each note"  mean? 
> 	The hammer can only do one thing as it approaches the string, and
> that is acheive a certain velocity. If Newton's (Sir Isaac) Laws are
> correct, full velocity is reached at the moment let off starts to
> occur.  The hammer is in acceleration to that point.  In the space
> past that point no acceleration can occur because the source of
> energy  has suddenly let off.  Since this let off occurs some
> distance from the string, the  hammer must then be decelerating, or
> loosing velocity as it strikes the string. Since let off is so close
> to the string the deceleration must be miniscual (sp? a word?) so we
> can envision the hammer velocity as the same at let off until
> striking the string. 
> 	But is this what is really happening?   Del suggests an idea by
> bringing up the "stiffness" factor in the shank.  Thus the hammer
> might be decelerating (or not accelerating as fast as the key is
> being pushed down) during the key blow because the shank is bending
> as a reaction to inertia. Because the hammer shank bends and  robs
> the  hammer of acceleration, this can be viewed as a waste of energy.
>  Perhaps the ideal shank would be one of ultimate stiffness, or one
> that doesn't bend at all.  
> 	On the other hand, a bent hammer shank may possess potential energy
> just as a bent bow ready to shoot the arrow.  So perhaps after let
> off, the bent shank tends to spring back and actually accelerates the
> hammer onto the string.  But maybe the paltry distance of 1/16 inch
> let off isn't enough for the bent shank to respond with its fullest
> energy potential.  Maybe a let off of say, 1/4 inch would give more
> space to allow more of this energy to be released. 
> 	Anyhow one can conclude that the let off of 1/16 (1.5mm) without
> considering hammer shank flex, is only concerned with the idea of 
> most contact with the key to acheive the greatest velocity  of the
> hammer. In that construct, the hammer shank stiffness cannot be a
> criterion. 
> 
> 	Finally all of the above is mostly moot if we want to consider  the
> most important phenomena, what happens to the string during and after
> hammer contact?
> 
> Richard The Space Jockey  
Dear Richard,
On the Yamaha silent series pianos the let-off is set further away from the
strings.  I wonder if these pianos could be measured against normal let-off
as far as de-celeration is concerned?
James Grebe
pianoman@inlink.com
> 
> ----------
> > From: Delwin D Fandrich <pianobuilders@olynet.com>
> > To: pianotech@ptg.org
> > Subject: Re: "Oval or Round Shanks"
> > Date: Tuesday, September 02, 1997 9:04 AM
> > 
> > The
> > hammershank is a beam.
> > 
> > The best hammershank shape would be one that is rectangular--not
> round
> > or oval--right out to the end where it would have to be made round
> to
> > fit the bored hole in the hammershank. The cross-section of this
> > rectangular hammershank, i.e., its width, could be varied as
> required to
> > meet the stiffness requirements of transferring the necessary
> energy to
> > the hammer mass of each note.
> > 
> > --ddf
> >