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

[Richard Moody]

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
>