NY Steinway Ribs and MC

[Stéphane Collin]

Hi Ric and all.

I take the opportunity of this thread to do the comparison with the default
protocol at Ciresa in Italy.
They insist that they can do anything on customer's specifications, but this
is what they do when the customer doesn't give any.

The ribs are flat to begin with.
The surface of the press on which the soundboard is put for ribs gluing and
crowning can be bended in variable modes, according to the soundboard
dimensions and the desired target crowning.
Panel moisture at gluing time is 8%
Ribs moisture at gluing time 8 - 10 %
Temperature of the hot box is 42° C  and relative humidity of the air inside
30 %

Crowning data for a board 150 cm x 220 cm large :

Rib 1 (treble side) 232 mm long, 1,5 mm between middle of the flat rib and
the curved board.
Rib 5 : 396 mm long, 3,5 mm ...
Rib 8 : 798 mm long, 10 mm ...
Rib 11 (maximum) : 1235 mm long, 18 mm ...
Rib 14 (last one) : 813 mm long, 9 mm ...

Remaining crown measured one week later in a 22,5 ° C  45% relative humidity
environment :

Rib 1 : 0,9 mm
Rib 5 : 1,9 mm
Rib 8 : 3,9 mm
Rib 11 : 8,8 mm
Rib 14 : 4,5 mm

I'm just discovering this part of the picture, but I'm sure these data will
mean more for all you who daily have your hands on it.
As always, your comments enlight my darkness.
Seems to me that in this process, the board is dried much less than in your
protocols.  Would this mean that these data are intended for a quite humid
climate ?
Also strikes me the small difference between board and ribs moisture
content.

Best regards.

Stéphane Collin.



-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Richard Brekne
Sent: dimanche 24 février 2008 11:44
To: pianotech at ptg.org
Subject: NY Steinway Ribs and MC

Hi Folks

Just got back from NY where I got the opportunity to do a long 
personalized tour of the factory.  As always one sees too much in too 
short a time to take it all in, but I had my eyes open for a couple 
special particulars.  When passing the rooms for soundboard and rib 
dry-down just prior to glue up I noted posted beside the doors the 
target MC for both.  So here is the absolute straight skinny.

Soundboards are dried to 3.8 to 4.5 % depending on the season. Ribs to 
8.6 %.  Both are put in their respective hotboxes for 3 days prior to 
glue up. The ribs are flat as we have been made to understand, and they 
glue them in shaped dish cauls (I saw glue up in the restoration room 
only f.o.s.) pressing the SB into shape and then ribs into resultant 
curves.  Bridges are cut to match the resultant curvature along its 
footprint by a computerized cutting machine.

This was very different from the Hamburg process. Hamburg did not use 
dished cauls do begin with, but individual cauls for each rib length.  
Nor did they have a dry down room for either prior to glue up.

I'm unsure of to what degree using dished cauls will affect the after 
glue up shape. Straining the panel in directions other then 
perpendicular to the grain before glue up ?? Have to think about that one :)

Anyways... this stands in contrast to the post I have referred to 
previously from John Patton I am unsure of why. It may be that they have 
some short waiting period between removing the panel and ribs from their 
respective hotboxes before actually gluing them together.  The rooms are 
quite warm and wood inside as well. Perhaps they need at least to let 
everything cool just a bit ?  The person guiding me was unsure of that 
answer and we didn't get the chance to confirm one way or the other.

Cheers
RicB