<!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>Ron N. and Del,</div> <div><br></div> <div>My thoughts concur with both your contributions, so its comforting to know that if I am way out in left field I'm not alone. Regarding the next two cut-off bars we're making, I've decided to laminate them. I designed the clamping system last year but didn't get around to building it. Wal had already cut up the RHS, so I should get it welded together by tonight (Sunday Sydney time).</div> <div><br></div> <div>Ron O.</div> <div><br></div> <blockquote type="cite" cite> <blockquote>----- Original Message -----</blockquote> <blockquote><b>From:</b> <a href="mailto:sec@overspianos.com.au">Ron Overs</a></blockquote> <blockquote><b>To:</b> <a href="mailto:pianotech@ptg.org">Pianotech</a></blockquote> <blockquote><b>Sent:</b> November 18, 2002 4:13 AM</blockquote> <blockquote><b>Subject:</b> Re: Belly rail crown - Why???</blockquote> <blockquote><br></blockquote> <blockquote>To listees concerned with sound board installation,</blockquote> <blockquote><br></blockquote> <blockquote>Again I find myself questioning a long standing tradition in piano making, and why it should be so done.</blockquote> <blockquote><br></blockquote> <blockquote>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>.<br> </blockquote> </blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">As well you should.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">In the above you bring up three assumptions I have questioned over the years. First, that the soundboard should be installed 'less stress.' Second, that there should be a rise in the center of the belly to accommodate the spherically shaped soundboard. And, third, that the shape of the soundboard should be spherical.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">The whole idea of soundboard crown and its subsequent physical distortion by the effect of string loading is to distort -- stress -- the thing.</font></blockquote> <blockquote type="cite" cite> <br> <blockquote>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.<br> </blockquote> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">As you say, no soundboard panel is crowned to a true spherical shape. More typically it will take on either a cylindrical shape or, possibly, a slightly conical shape.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">With only one exception that I am aware of no manufacturer has shaped a rim to accommodate a spherical soundboard shape and that was Kimball in its later years. Of course by then they were using laminated soundboards exclusively. Some vertical piano makers do shape their soundboard liners to a more-or-less spherical shape but it is generally only a fraction of the shaping that would be required to really match the claimed shape of the soundboard assembly.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">At best crowning the bellyrail takes care of only one relatively short span of the soundboards edge. What about the rest?</font></blockquote> <blockquote type="cite" cite> <br> <blockquote>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.<br> </blockquote> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">It is my practice to set the rim and bellyrail, including the soundboard cutoff rail, flat. Since the soundboard will be stressed -- i.e., have considerably less crown -- once the strings go on I prefer to have a flat, consistent mounting surface for the parameter of the board. Besides, my cutoff bars tend to be so shaped that very little of the soundboard is actually glued to the bellyrail.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">And, while we're on the subject, for the same reasons I fail to see any advantage to beveling the inner rim to (supposedly) accommodate the shape of the soundboard. It is claimed that this somehow aids the maintenance of crown but I surely don't see how. To illustrate simply clamp a piece of spruce to a bench and see how easily it is bent.</font></blockquote> <blockquote type="cite" cite> </blockquote> <blockquote type="cite" cite><font face="Comic Sans MS" color="#000080">Del</font></blockquote> <blockquote type="cite" cite> </blockquote> <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>