The Richard Gertz myth

[gordon stelter]

Well, if it's not Gertz's invention, why do so many  (
all? ) old M&H's still sound like rolling thunder when
the board is riddled with cracks and the whole thing
is a dilapidated mess?
     Thump


--- Phillip Ford <fordpiano@earthlink.net> wrote:

> >All,
> >
> >Back in 1900, if the patents-office examiner had
> been paying attention, 
> >Richard Gertz never would have got his patent. The
> sound board of a real 
> >world piano does not push outward as downbearing is
> applied. While the 
> >sound board shown in the piano diagram at Mason and
> Hamlin's website 
> >(http://www.masonhamlin.com/crown/crown.html) might
> push outwards, real 
> >pianos do not have the sound board ribs offset
> higher than the cord-line 
> >as shown in their image (a jpeg conversion of the
> M&H website image is 
> >shown below).
> 
> Ron,
> 
> Would you explain what you mean by the cord line?
> 
> >...
> >So yes, a substantial back beam configuration is a
> good thing, but the 
> >Richard Gertz 'crown retention system' will be of
> virtually zero assistance.
> >
> >Ron O.
> 
> Unless it works in both directions, in which case
> it's essentially doing 
> the same job as the back beams.  It's not clear that
> it does from the 
> diagrams on the M-H site (which diagrams are hard to
> read, BTW, since they 
> chose to use red lettering on a black background). 
> I don't know if those 
> long bolts are a press fit in the holes in the rim
> or not.  There certainly 
> seems to be a gap between the bolt head and the
> outer rim which would seem 
> at first glance to allow the bolt to move outward,
> offering no resistance 
> to the inward movement of the rim.  On older M-H
> pianos the rods were 
> attached to tapered plugs in the inner rim which
> were captive by the outer 
> rim.  You can see drawings of this on the patent,
> No. 783,781.  I believe 
> that this assembly would form quite a rigid frame. 
> Those rods may look 
> insubstantial next to the large softwood beams
> beneath them, but because 
> they are steel, each of them provides the stiffness
> of a large softwood 
> beam.  Assuming a 20 mm diameter rod and a modulus
> for softwood of 10 GPa 
> and steel of 200 GPa, then each rod is equivalent to
> a softwood beam of 63 cm^2.
> Bump the rod up to 25 mm and it's equivalent to a
> softwood beam of 
> 98 cm^2 (15.2 in^2 - roughly a 2.5 in. x 6 in.
> beam), which I would 
> consider a fairly massive beam.  It's my feeling
> that if this device were 
> properly designed, then the wooden frame members
> would be superfluous.  A 
> property of the steel is that it is consistent in
> strength and stiffness, 
> which is not the case with the softwood (for those
> that value consistency 
> from piano to piano).  A downside may be that this
> type of frame would be 
> more expensive and heavier than the softwood frame,
> but I wouldn't think 
> significantly so.  Also, the centerline or line of
> action of the 'spider' 
> could be closer to the centerline of the soundboard,
> since the spider needs 
> less physical space.  On the other hand, because it
> has less vertical 
> depth, it's probably not very good at resisting
> twisting of the rim, the 
> way a 15 cm deep beam would be.
> 
> Looking at the M-H page that you mentioned I also
> noticed a couple of other 
> things that I hadn't noticed before.  They're
> expecting not only the rim to 
> act against the soundboard panel to resist board
> flattening, but the rim 
> acting on the end grain of the ribs to resist
> flattening of the 
> board.  They also make a point of mentioning that
> the grain of the ribs is 
> perpendicular to the grain of the rim.  I'm not sure
> why they think that's 
> important, and I'm not sure how that can be the case
> unless the ribs were 
> at 90 degrees to the rim at the points where they
> intersect the rim, which 
> is almost never the case.  They also seem to think
> that white spruce is 
> stronger than Sitka spruce.
> 
> Phil Ford
> 
> 
> 
> 
> Phillip Ford
> Piano Service and Restoration
> San Francisco, CA
> _______________________________________________
> pianotech list info:
> https://www.moypiano.com/resources/#archives
> 



		
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