<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Re: Belly rail crown - Why???</TITLE> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <STYLE type=text/css>BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } </STYLE> <META content="MSHTML 5.50.4134.600" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><FONT face="Comic Sans MS" color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B> <A title=sec@overspianos.com.au = href="mailto:sec@overspianos.com.au">Ron Overs</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> November 18, 2002 4:13 = AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Belly rail crown - = Why???</DIV> <DIV><BR></DIV> <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></BLOCKQUOTE> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>As well you should.</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <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></BLOCKQUOTE> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <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></BLOCKQUOTE> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><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></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080></FONT> </DIV> <DIV dir=ltr><FONT face="Comic Sans MS" = color=#000080>Del</FONT></DIV> <DIV dir=ltr><FONT face="Comic Sans MS" color=#000080></FONT> </DIV></BODY></HTML>