<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Belly rail crown - Why???</title></head><body> <div>To listees concerned with sound board installation,</div> <div><br></div> <div>Again I find myself questioning a long standing tradition in piano making, and why it should be so done.</div> <div><br></div> <div>The theory of sound board curvature<font color="#0000FF"> (whatever that might be)</font> tells us that the shape of a sound board panel ideally should conform to that of a sector of a sphere. Since it has been decided that the sound board should be installed so that it experiences less stress, makers historically have decided that there must be a rise in the centre of the belly rail to accommodate the spherically shaped 'board<font color="#0000FF"> (6mm or 1/4" would seem to be a typical figure)</font>.</div> <div><br></div> <div>I am wondering about the validity of this practice, since the board does not in reality assume a spherical shape. It would appear to be crowned more or less perpendicular to the 'line' of the long bridge, ie. along the line of the ribs. Furthermore, the treble corner tends to curl up like a potato crisp after the ribs have been fitted, which would cause the raised centre of the belly rail to place the glued down belly under even greater stress than if the belly rail was made straight.</div> <div><br></div> <div>Just sitting at an empty case thinking about this, I can see no disadvantage in setting the belly rail straight. In fact with the piano I am setting up at present, the cut off bar extends so far across to the treble end of belly rail that the 'board will not be supported by the belly rail until the highest treble section is reached. The cut off rail I am building is a continuously curved member of 30 mm depth and 40 mm wide. It will be glued to the back posts, and the entire non-sound board bass corner will be filled in with a 19 mm thick plywood piece which will butt up to the sound board panel over the cut off bar. This is intended to provide a high level of lateral support for the cut off bar and sound board perimeter. I can see no advantage in setting any part of the sound board perimeter at a height other than that of the inner rim.</div> <div><br></div> <div>Dale, Del, Ron N. etc. what are your thoughts on this matter.</div> <div><br></div> <div>Ron O.</div> <div><br></div> <div><br></div> <x-sigsep><pre>-- </pre></x-sigsep> <div>_______________________<br> <br> OVERS PIANOS - SYDNEY<br> Grand Piano Manufacturers<br> <br> Web: http://overspianos.com.au<br> mailto:info@overspianos.com.au<br> _______________________</div> </body> </html>