Inertia, was "Grand Touch"

[Michael Spalding]

Dean,

Please read my comments to Ed re:  Math, Debate, Experiment.

Mike


> [Original Message]
> From: Dean May <deanmay at pianorebuilders.com>
> To: Pianotech List <pianotech at ptg.org>
> Date: 7/14/2006 9:19:08 PM
> Subject: RE: Inertia, was "Grand Touch"
>
> Mike wrote:
> At the midpoint of a 1/2" hole in a 1" tall key, the
> stiffness is reduced by approx. 12%.  Is this negligible, or can a
> sensitive pianist feel the difference?  
>
>
>
> You are technically correct. Actually, according to my quick and dirty
> calculations, the rigidity of the keystick is reduced about 18%, assuming
> the lead does nothing to add to the stiffness. But, as you say, that is at
> the midpoint of the hole, a very narrow region of the key. The reduction
of
> stiffness on either side of the hole is reduced exponentially as one moves
> to either side of the midpoint. 
>
> So what are we talking about? Flexure of the keystick occurs as a sum
total
> of infinitesimal strains along the keystick, from the front to the back.
But
> it is certainly not uniform. At the front and back there is no flexure.
The
> maximum strain occurs at the balance rail hole where the maximum bending
> stress occurs and it decreases linearly to the front and to the back of
the
> keystick. Integrate all of the micro strains along the keystick and you'll
> get the total flex. 
>
> The question, then, is how much will the total flexure change because of
an
> 18% reduction in stiffness in 4 very narrow regions of the key where the
> bending stress is 30-50% of it's maximum? I don't want to do the calculus
> but I'll stand by my statement that it is very negligible. 
>
> Ron N's fix of adding the hardwood shoe at the balance rail hole on the
> other hand will make a huuuge difference. Why? Because he is increasing
the
> stiffness at the outer fibers where it does the most good: at the point of
> the greatest weakness (balance rail hole goes through the outer web) where
> the key is experiencing its greatest bending stress. My quick and dirty
> calculations show the balance rail hole reduces the stiffness of the key
at
> that point of greatest strain by at least 40%.
>
> The weakening effect of that balance rail hole on the keystick beam cannot
> be overstated. It is the weak link in the system. The effect of any hole
> drilled for leads pales in comparison. I suspect cracks between the holes
> occur not because of bending stress per se, but because of the internal
> stress placed on the wood by swedging the leads in holes too close
together.
>
>
> But I've been wrong before. :-)
>
> Dean
>
>
>
> -----Original Message-----
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
Behalf
> Of Michael Spalding
> Sent: Friday, July 14, 2006 5:58 PM
> To: Pianotech List
> Subject: RE: Inertia, was "Grand Touch"
>
> Dean,
>
> Think for a moment about the assumptions behind your statement.  Do you
> assume the key material is homogeneous and isotropic?  Ever see a key with
> 3 or 4 closely spaced 1/2 inch leads with cracks in the wood connecting
> some or all of the lead holes?  Text book formulae are one thing, the real
> world is  another.  At the midpoint of a 1/2" hole in a 1" tall key, the
> stiffness is reduced by approx. 12%.  Is this negligible, or can a
> sensitive pianist feel the difference?  What about 2 holes, or 3 or 4? 
> Worth testing on actual components, I say.
>
> Mike
>
>
> > [Original Message]
> > From: Dean May <deanmay at pianorebuilders.com>
> > To: Pianotech List <pianotech at ptg.org>
> > Date: 7/13/2006 9:53:51 AM
> > Subject: RE: Inertia, was "Grand Touch"
> >
> > The stress is all carried by the upper and lower fibers of the wood.
Holes
> > in the middle have negligible effect. Think I-beam. All the stress is
> > carried by the upper and lower webs. You don't want to drill holes in
> them.
> > You can, however, drill through the connecting center web with no loss
of
> > strength.
> >
> > Dean
> >
> > -----Original Message-----
> > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
> Behalf
> > Of Michael Spalding
> > Sent: Thursday, July 13, 2006 9:31 AM
> > To: Pianotech List
> > Subject: Re: Inertia, was "Grand Touch"
> >
> > Jude,
> >
> > I think it's great thatyou will be testing this experimentally.  One
> factor
> > you might want to look at is how the lead holes in the keystick affect
its
> > flexibility.  It seems to me that a keystick with several large led
holes
> > close to the balance pin would flex more on a hard blow than one with
> fewer
> > or smaller holes further away from the balance pin.  Looking forward to
> > hearing and discussing y our results.
> > \
> > Mike
> >
> >
> > > [Original Message]
> > > From: Absolute Piano <absolutepiano at comcast.net>
> > > To: Pianotech List <pianotech at ptg.org>
> > > Date: 7/12/2006 9:02:37 PM
> > > Subject: Re: Inertia, was "Grand Touch"
> > >
> > > Thanks Vladan and all for all the info.
> > >
> > > There is a lot to chew on. My interest is in the practical
application.
> > Why 
> > > is it that two keys with the same balance weight and the same front
> > weight 
> > > but leads arranged differently seem to me to feel the same?
> > >
> > > I ask because I had a customer that asked me to place all the leads
> > closer 
> > > to the front and to use less leads after I had already set up the FW
to
> > my 
> > > specification in a new keyboard using a tower pattern nice and close
to
> > the 
> > > balance rail. I went through all the trouble but as far as I or anyone
> > else 
> > > could tell the action felt the same.
> > >
> > > I'm in the process of building several action models to test the
science
> > as 
> > > I am slowly digesting it so you are all being quite helpful.
> > Unfortunately 
> > > with reality hanging over me it may take awhile to report back any
> > results.
> > >
> > > Best,
> > >
> > > Jude Reveley, RPT
> > > Absolute Piano Restoration, LLC
> > > Boston, Massachusetts 
> > >
> >
> >
> >
> >
>
>
>
>