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 > <BR><BR><BR>**************<BR>Looking for a car that's sporty, fun and > fits > > in your budget? Read reviews on AOL Autos.<BR> > (http://autos.aol.com/cars-BMW-128-2008/expert-review?ncid=aolaut00050000000 > 017 )</HTML> > > >
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