[pianotech] Belly talk

[Dale Erwin]

 Hi Jim
  I get it. Its not a perfect system. One thought though.... and it is this. Many bellymen /piano companies glue the bridge to the board on a crowned trestle ie. or along the grain. Now I don't do that routinely. But it does induce a crown along the grain/bridge making it effectively a double crowned  or more dome shaped than simply crowned across the grain. A more 3 dimensional object it would seem or am I missing something here.
   On those few occasions when I attached the bridges this way (double crowned)I found that I could set the sound board in the case without forcing down the treble and bass end. They just plopped into place with no bending stress. To me that infers that is was perhaps a closer mate or match to the rim more generally than doing it the way I typically do it. We force crown the board a bit any way or I do and it doesn't take that much force to bend a board along the grain some amount say approx. 70 to 90 ft radius


  In the case cited the piano in question was an Stwy A-2 and having done quite a few A-2s both ways it was my subjective opinion at the time the sound was more lively and had more freedom than not double crowning it. I am considering going back to that format. 

This means, either way, 
flat or rastened, even if rastened perfectly, localized stress is added 
to the panel edge at gluedown.
Jim, but he bending stress is negligible & therefore IMO.... a non issue. There is no way to quantify every
thing we do in terms of sound. We either like it or we don't.
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 7:53 am
Subject: [pianotech]  Belly talk


Dale said:

<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.

This is precisely the point I'm trying to make.  You "prove" the bevel 
and its orientation by placing a simple 2 dimensional straight edge at 
some arbitrary point and see a bevel of some sort. Then infer this 2 
dimensionality to a 3 dimensional soundboard panel, which is not domed 
but crowned across the grain(roughly), and variable throughout, because 
the rib arc lengths vary. Where is this 1.5 deg bevel at the bass end of 
the board when we beat the panel tail into submission??

Further, the 1.5 deg bevel is not matching the "dome" in a cc board, 
since a 60' or even 40' radius board would be meeting the rim at less 
than 1 deg, depending on the length of the rib.  This means, either way, 
flat or rastened, even if rastened perfectly, localized stress is added 
to the panel edge at gluedown.

Jim Ialeggio


-- 
Jim Ialeggio	
jim at grandpianosolutions.com
978 425-9026
Shirley Center, MA


 
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