MH BB Pinblock

[Fenton Murray]

Nick,
Great to see you come in on this. I love your writing, reminds me of the old 
'Good Vibrations' in the PTJ.
Fenton
----- Original Message ----- 
From: "Nick Gravagne" <gravagnegang at att.net>
To: "'Pianotech List'" <pianotech at ptg.org>
Sent: Saturday, August 02, 2008 9:25 AM
Subject: RE: MH BB Pinblock


> Hi All,
>
> For what it is worth it is interesting to consider the forces acting on 
> the
> pinblock by the immense pull of the strings. Steinways and M&Hs do not 
> come
> equipped with plate bushings, thus the rearward pull of the aggregate
> tension is uncompromisingly transferred via the tuning pins directly to 
> the
> pinblock wood, and thence to the plate flange for resistance.
>
> But that is only part of the story; we also have a significant downward
> force acting on the block as well. Assuming a 5 degree lean-back of the
> tuning pin and a 160 pound pull (and much higher in the bass) of a single
> piano string, the axial load down the center of a single pin would be 
> about
> 14 pounds (a 4 degree lean would cause an 11 pound axial force). The 
> tuning
> pins are thus charged or "energized", and the force is directed downward 
> to
> the pinblock. The 5 degree lean-back on all the pins would cause a 
> combined
> downward force of about 3000 pounds. With zero degree lean-back there is 
> no
> such direct downward force at all.
>
> The pinblock is also acted on by a significant rotational force or moment 
> as
> well. The force to rotate the block down at the plate flange and up at the
> stretcher amounts to about 1500 foot pounds (depending on where we assign
> the actual point of rotation), and much of this is resisted also by the 
> bass
> and treble supports and fit of the block all around. I have not double
> checked my math and trig, but it seems correct to me.
>
> The factors acting to keep all in equilibrium are several: a firm fit of 
> the
> block to the plate flange (most critical), the bass and treble rim 
> supports,
> a firm fit to the stretcher, the strength of the plate webbing and bracing
> there, and lastly, our lowly plate screws. Given a good pinblock fit all
> around, and a reasonable amount of cast iron and bracing, a higher tension
> scale should require more plate screws - and that is what we see in the
> higher-tensioned and larger pianos in general.
>
> Still, having said all that, it comes down to a matter of choice. Plenty 
> of
> examples of well built and fine sounding pianos do not have blocks rigidly
> attached to the stretcher, and some cannot, like the Chickering I am
> currently working on. However, I think there is something to be said for
> full-fit treatment where the original block was so installed. Regarding 
> the
> Mason in question here, we all know that most original Mason grands come
> equipped with full-fit blocks. That would guide me if nothing else.
>
> Nick Gravagne, RPT
> Piano Technicians Guild
> Member Society Manufacturing Engineers
> Voice Mail 928-476-4143
>
> -----Original Message-----
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On 
> Behalf
> Of A440A at aol.com
> Sent: Saturday, August 02, 2008 7:31 AM
> To: pianotech at ptg.org
> Subject: Re: MH BB Pinblock
>
> David writes:
>
> << pinblock is screwed to the inner rim via a couple of plate screws that
> penetrate the block down to the rim) all the way to the stretcher why 
> would
> you need to attach the pinblock to the stretcher to create case stability.
>
>>>
>
> I don't think it is a question of case stability, but rather, stiffness in
> the plate/block assembly.
>    The attachment of the block to the stretcher assists the block in
> resisting  movment of the strings in the vertical plane.  These vibrations
> are quite
> small, but I consider them important, and without some vertical component 
> to
>
> the "beam" that resists them, more energy is lost to heat than otherwise
> would
> be.
>   It could be that the increased stiffness afforded by attaching the block
> to the stretcher would also increase the entrainment of the strings'
> vibration
> to the case.
> Regards,
>
> Ed Foote RPT
> http://www.uk-piano.org/edfoote/index.html
> www.uk-piano.org/edfoote/well_tempered_piano.html
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