<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html> <head> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii"> <meta name=Generator content="Microsoft Word 10 (filtered)"> <title>Re: Soundboard drydown for installation</title> <style>  </style> </head> <body lang=EN-US link=blue vlink=blue> <div class=Section1> <p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size: 10.0pt;font-family:Arial;color:navy'>Nice illustration.  I would be curious to see or hear about the jigs people use to crown ribs when they are not crowing by bending and laminating.  </span></font></p> <p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size: 10.0pt;font-family:Arial;color:navy'> </span></font></p> <div> <p><font size=2 color=navy face="Times New Roman"><span style='font-size:10.0pt; color:navy'>David Love</span></font><font size=2 color=navy><span style='font-size:10.0pt;color:navy'><br> davidlovepianos@comcast.net<br> www.davidlovepianos.com</span></font><font color=navy><span style='color:navy'> </span></font></p> </div> <p class=MsoNormal style='margin-left:.5in'><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>-----Original Message-----<br> <b><span style='font-weight:bold'>From:</span></b> pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] <b><span style='font-weight:bold'>On Behalf Of </span></b></span></font><font size=2 face=Tahoma><span style='font-size: 10.0pt;font-family:Tahoma'>John</span></font><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Delacour<br> <b><span style='font-weight:bold'>Sent:</span></b> Saturday, January 19, 2008 2:05 PM<br> <b><span style='font-weight:bold'>To:</span></b> </span></font><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>Pianotech List</span></font><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'><br> <b><span style='font-weight:bold'>Subject:</span></b> Re: Soundboard drydown for installation</span></font></p> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>At 10:45 -0500 19/1/08, Farrell wrote:</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <blockquote style='margin-top:5.0pt;margin-bottom:5.0pt' type=cite cite> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Again, I agree with Ron - the darn thing won't crown anyway from rim constraint.</span></font></p> </blockquote> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Quite so, but let's leave opinion aside and look at the reality of the matter, which seems to be something like this.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Consider a section of soundboard 6" wide with one rib.  Consider them first separately.  Which will it be easier to bend a certain amount?  No contest : the 6" strip of board will bend with the slightest effort and the rib with great difficulty.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>The picture below is a scale drawing, which you can see (using Firefox or Opera or Safari) as an SVG file which you can enlarge if you wish. Click <a href="http://pianomaker.co.uk/technical/temp/crown.svg">here</a> or on the image to view the file.  How to zoom it will depend on your browser.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'><a href="http://pianomaker.co.uk/technical/temp/crown.svg"><span style='text-decoration: none'><img border=0 width=450 height=104 src="cid:image001.jpg@01C85AAB.E0B9F590"></span></a></span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>I have exaggerated the crown to a radius of 15ft.  The length of the section is 500 mm.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Note that lines of force acting between the two red lines run mainly through the rib, preponderating if anything slightly towards the top of the rib.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>When wood takes on moisture it expands, as we all know, but it doesn't expand isotropically -- far from it; the expansion along the grain is practically negligeable in comparison to the expansion across the grain.  I'm not looking at any figures at the moment but I imagine the difference for softwoods is even more marked.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>So the assembly takes on moisture... not only does the rib expand as a result by but a negligeable amount but whatever expansion there is will tend if anything to make it bend downwards and reduce the crown.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>As you have just pointed out, spruce compresses very easily across the grain has  low elasticity across the grain.  Whatever expansion there is of the soundboard across the grain (left to right in the picture), and there will be significant expansion, will result in compression of the wood within or beyond the yield point, but any power it might have to make any difference to the crown will be completely negated by the action of the rib and the forces to which this is subjected.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Incidentally I have drawn the rib as it would be in a soundboard made in the English fashion, ie. planed to radius before assembly and planed straight on the underside after the assembly has settled down to the normal environment.</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>JD</span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> <div> <p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> </span></font></p> </div> </div> </body> </html>