[pianotech] Belly talk

[David Love]

A bit of an overreaction.  No hypocritical pontification that I've heard,
for that matter not much pontification at all.  Simple comments for the sake
of discussion.    

The stress I was referring to (don't know about others) was more to do with
the glue joint than the panel.  With modern glues the stress at that joint
is probably not significant.  But with hide glue maybe it is.  If you bend
the panel enough there to bring it down to the inner edge of the inner rim
when the rim is not beveled there probably is a fair amount of pulling apart
stress on that point and it probably made sense to insure that that point of
contact was as stress free as possible.  The amount of panel bending at the
rim may not be significant enough to impact the sound but what benefit could
there be to not having a bevel to at least more closely match the panel
landing area?  Why introduce additional stress to the panel by forcing it
into an additional bend there?  If you are using more conventional rib
crowning methods (or, for that matter none at all) I can see where using a
beveled rastern to help introduce additional crown into the panel could be a
benefit. Once glued down to an immobile rim, the dome shape would add some
wanted stiffness to the entire assembly.   That being said, I've certainly
glued in soundboards where the rastern was not beveled.  I can't say I
noticed a difference but how would you know?  It's hard to do a side by side
comparison and harder to separate out the relative contributions of the rib
scale versus the minimal crowning effect of the beveled rastern.  

As far as the other issues go.  No smoke screen necessary.  I've abandoned
variable and super tight radius ribs as unnecessary and sometimes
counterproductive.  Similarly the treble fish.  I find too much stiffness to
be as objectionable as too little (sometimes more so) and there is a danger
there with both those features.  For that matter, I've also abandoned the
1/3, 1/3, 1/3 tapering pattering for a more conventional approach especially
in the top of the piano where excess stiffness is objectionable.  However,
with the 1/3, 1/3, 1/3 rib tapering an argument can well be made to insure
that the rastern is beveled since the ribs tend to be stiffer near the rim.

Cut off bars do present a problem (mine tend to be more modest when I use
them and I don't always, nor find them necessary with an adequately designed
ribscale).  They do add a certain control to the sound but that's a two
edged sword.  Boards without cutoffs can have more "life".  I've found the
best solution is to go ahead and angle the cutoff slightly to more closely
match the bevel and then cut the panel along the cut-off and glue on the
corner panel separately.  That avoids the "s" bend at the joint there.
However, I've also just installed the cut-off flat and just forced down the
panel onto it for that short section.  The pianos I've taken apart that have
existing cut-offs don't seem to be beveled even if the rest of the rastern
is.     

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Friday, November 30, 2012 8:24 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Belly talk


It's interesting how many unconnected dots there are in this discussion. 
For instance, it's presumed and generally agreed that the rasten (where did
that word come from, incidentally?) ought to be beveled to "match" 
the landing angle of the soundboard to minimize undue stress on
installation. So since this seems to be an acceptable premise for most, a
few questions come to mind. Have any of you who have installed soundboards
have actually measured or calculated the panel landing angle and compared
that with that of the rasten? Who has then adjusted the rasten bevel angle
to accommodate the panel? How about the relatively recent tribe of
redesigners using multiple rib radii? Tighter radii will need steeper rasten
bevels to match. Does anyone do this? How about bass cutoff bars? How do you
bevel the tops of these to match the panel angle? Or do you? How about the
fish in the treble? Rib radii in the treble of "typical" redesigns tend to
be pretty tight, like in the 4-6M radius range. How do you contour the fish
to match the panel? Does anyone do this? If so, how about some details? If
not, why all this hypocritical pontification about matching rasten bevels to
panel landing angles to minimize panel stress if you don't bother to do it?
I'll tell you up front that I don't bother and don't think it means anything
anywhere near worth the posturing and pretending it typically gets. With
more people all the time exploring soundboard design and function, it seems
to me like a good time to clear up some of this glaringly contradictory
stuff. It's okay. Nobody's looking. You can come out from behind the smoke
screen and fess up. Trust me, no one will notice and the world will go back
to exactly like it was by morning. No darkness will be unduly illuminated.

Ron N