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

[Marcel Carey]

Richard & List,

I think that you forget to take into consideration the decceleration of the
hammer when it hits the string. The decceleration is much much more than the
acceleration. The hammer stops right there and then the shank will have to
flex to absorb that decceleration. The hammer has about 1-7/8" to accelerate
as it stops almost on the string (mind you, I know the string will move
around a bit). I think this is where the shanks flexibility will affect the
string contact time. And we all know that string contact time equals
voicing. So there must be an ideal compromise to be made depending on pianos
in order to get the "ideal" power to tone ratio.

Who knows, even I could be right.

Marcel Carey, RPT

At 00:48 97-09-04 -0500, you wrote:
>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  
>
>----------
>> 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
>> 
>
>