Cut-Off Bar Attachment & Floating Rim

[Ron Overs]

At 4:04 PM -0400 19/10/02, Farrell wrote:
>Should a cut-off bar (also called a dumb bar, I think) be attached 
>to the backpost?

Ideally, for improved structural integrity - Yes.

>  I have one that has one end on top of middle-fo-the-piano backpost 
>and the other end at the side/edge post. It crosses over another 
>backpost. It is not attached at all - although you could only slip a 
>piece of paper in between them. I should think this a possible 
>source for a buzz.

Indeed it could.

>  But more importantly, I should think it advantageous to attach the 
>cut-off bar as securely as is possible, and anywhere possible. Is 
>there any reason to have it floating next to an available backpost?

To great extent, this will depend on whether the bar is installed 
into the piano with the board, or before the sound board is fitted. 
If the bar is first fitted to the sound board and both are installed 
into the case simultaneously, it is most practical to allow for a 
clearance between the bar and back post (this is the most common 
scenario and the weaker of the two options, eg. Bechstein, Blüthner, 
Bösendorfer and Stuart). This is common practice since it is 
difficult to achieve a good fit between the sound board/inner rim, 
and the bar/back post joints simultaneously. However, if the bar is 
fitted to the case prior to installing the sound board, then the bar 
should be attached also to the back post. This will greatly improve 
the rigidity of the sound board perimeter and improve slightly the 
sustaining qualities of the instrument.

For our next two 225 grand pianos, now under construction, the cut 
off bars will be of a substantial curved hardwood section (with an 
ADD of 0.77 gr/cc) and fitted to the case prior to the installation 
of the sound board. The cutoff bars will therefore also be glued and 
doweled to the back posts, and the sound board perimeter will follow 
the curve of the cut off bars. Furthermore, there will be no sound 
board spruce covering the bass corner area  (which I believe to be a 
waste of good spruce). This area will be filled with a structural ply 
(veneered with the same material as the inner surface of the outer 
rim) which will further strengthen the structurally integrity of the 
cut off.

Ron O.
-- 
_______________________

OVERS PIANOS - SYDNEY
Grand Piano Manufacturers

Web: http://overspianos.com.au
mailto:info@overspianos.com.au
_______________________