[pianotech] Belly talk

[Nicholas Gravagne]

On Sat, Dec 1, 2012 at 8:36 AM, Dale Erwin <erwinspiano at aol.com> wrote:

>  At some point my eyes kind of glaze over with splittin hairs on certain
> things and this is one.


Agreed, Dale.

So I see it this way thru my smoke and mirrors.
> The inner rim has an approx 1 1/2 degree bevel cut into the inner rim at
> the factory. Set a straight edge on it & it becomes apparent.
>   We have a soundboard, be it rib crowned or other wise crowned. I don't
> care. It is dome shaped.
>

Agreed; though at first, coming out of the rib press, whatever that may be,
the board and rib assembly is more channeled across the panel grain than
dome-shaped over all. Gluing on the bridge (assuming the bridge is hollowed
underneath, as most are) begins the process of forming the dome, but it is
after gluing to the rim that the board and rib assembly takes on a more
decidedly domical shape than channeled.

The shape of a dome is exceedingly rigid for its light weight. A clear
advantage for our needs. A dome is a three-dimensional support system. A
beam, whether crowned or not is the first dimension, a legitimate arch is
the second (channeled) and the dome being the third (take an arch and spin
it and you have a dome). With each successive progression from beam to dome
comes order of magnitude load-resisting capabilities.


> So it has an angle at the edges. or...said another way...It is not flat.
>  It rises in elevation from the edge to the highest point in the board.
> So whats wrong with having an approximation of that angle cut into the
> inner rim which will match the rise in elevation of the board in some
> approximation.
>

Agreed. This reality, it seems to me, should not even be in question.
Though, to be clear, the "highest point in the board" would actually exist
below the point that would be established by a 1.5 degree rim angle, given
that that a linear uphill rise off the rim would not begin to round off and
slope downward as would the curve of a soundboard, be it a circle or
parabola or whatever.

Not a damn thing and not everyone in a factory who ever designed a piano
> their way is an idiot Ron.
>
> For what its worth I have glued in several boards to inner rims that were
> cut flat and it does indeed flatten out the board a little. \
>

For sure.


> I'd prefer that not to happen. Do I cut the rim trying to match some
> idealized rise in elevation.
>

Technically and geometrically, the rim angle would have to change in direct
proportion to the rib length (or for that matter to the constantly varying
cross-grain length of the panel). Shorter ribs form less angle at their
ends. This would be a difficult process to achieve and would be, in my
view, a waste of time. Given that the shorter ribs imply less of a required
angle at the rim, if the rim is angled /  beveled at a more or less
constant 1.5 degree, the shorter ribs would have to pressed down into the
rim "pocket" as these would  not normally mate, the rim angle being deeper
than the angle naturally formed at the end of the rib / board. I prefer
more than less, the 1.5 degree angle being a minimum. No harm done, and
only an advantage to be gained. Interestingly, increasing or assuring the
rim angle is fairly easily accomplished with a small red devil handled
scraper. We do it  here all the time. See
http://www.amazon.com/dp/B001SBJIC6/ref=asc_df_B001SBJIC62286157?smid=AXPVI82I57KZA&tag=sdcbing4-20&linkCode=asn&creative=395105&creativeASIN=B001SBJIC6
for the scraper. When sharp, this tool is amazing.

No. A waste of time.  But to be sure.... No one would want the inner rim to
> be beveled in the opposite direction. Would they?
>

Right.


> jeez
>


> Dale
>
> *Dale Erwin R.P.T.
> Erwin's Piano Restoration Inc.
> ** Mason & Hamlin/Steinway/U.S. pianos
> www.Erwinspiano.com
> Phone: 209-577-8397
> *
>
>
>
>
>
> -----Original Message-----
> From: Jim Ialeggio <jim at grandpianosolutions.com>
> To: pianotech <pianotech at ptg.org>
> Sent: Sat, Dec 1, 2012 7:17 am
> Subject: [pianotech] Belly talk
>
>  Right...
>
> Regarding the "rasten", I'd like to take a step back, and come at this
> from a "what is physically possible" perspective.
>
> For the moment lets leave all design intent aside and look at this from
> a what is physically possible perspective.  The question is "what are
> rebuilders actually achieving when they do this, as opposed to what do
> they think they are achieving".  To be clear, I'm not talking about
> tonal results here. I'm simply talking about whether, if one of us said
> they were going to bevel so-and-so piece of wood at such-and such angle,
> they actually did what they set out to do...ie the "as built" wooden
> joint matched their intent.
>
> As someone with a background in setting up production runs where
> hundreds of 5 surface profiled joints had to fit dead nuts without hand
> adjustment, I had to learn how to prove what I was actually achieving in
> a particular process rather than assuming that I had achieved what I set
> out to achieve, wished to achieve, or though I achieved. Learning how to
> prove the "as built" conditions is a challenging task, much harder than
> one would expect, until one learns how to create and maintain
> trustworthy indexes.
>
> For any of us the "as built" and the intent can sometimes be wildy
> different things. Further, its hard enough to match intent to result in
> set ups where the parts are all straight lines, but with a piano where
> straight lines are few and far between, and joints are cut in tough to
> access places, its a whole other kettle of fish.
>
> I find this tug between intent and achieved results again and again in
> piano work.  In this work the tug is accentuated because there simply is
> not a trustworthy reference point or index surface to be had, unless one
> purposely sets out to create and prove one, and then refer and correct
> all work back to that known index.
>
> So my take on this is, given my background, simply that the mating angle
> at the "rasten" is highly variable both from the rim's and the panel's
> perspective and thus unknown in its "as built" reality.  At least from a
> rebuilder's perspective, the rasten joint is physically impossible to
> actually achieve with the intent techs claim they are shooting for.  It
> only introduces complexity where the complexity takes on a mind of its
> own. I see the added complexity trying to control such a miniscule
> detail becoming gratuitous, and even worse fueling speculations about
> what one achieved without proving that one actually created the intended
> physical joint.
>
> This in addition to whether there is any tonal advantage at all in
> theory. However this is hypothetical anyway, because probably its never
> actually been accomplished.
>
> Add to this, that the majority of the "rasten" is along the short
> extremely flexible grain of the panel, and the claims of its value
> become more and more questionable.
>
> Jim Ialeggio
>
> --
> Jim Ialeggio	jim at grandpianosolutions.com978 425-9026
> Shirley Center, MA
>
>
>


-- 
Nick Gravagne, RPT
AST Mechanical Engineering
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