<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Plywood shrinkage??? Laminated soundboards???</title></head><body> <div>Hi Sarah,</div> <div><br></div> <div>I would like to add a couple of comments re your observations, additional to Del's recent post.</div> <div><br></div> <blockquote type="cite" cite><font face="Arial" size="-1">My friend and I were examining some antique furniture, figuring out how we are going to restore it.  I noticed that many drawer bottoms in several pieces were made of thin plywood and, further, that the plywood panels were almost universally shrunken by perhaps 1% of their original size (e.g. 1/4" over a 25" span).</font></blockquote> <div><br></div> <div>The draw bottoms were most likely not coated with any finish to slow moisture transmission, and secondly they would be manufactured from material which was sliced through the flitch, so the grain orientation would be almost certainly 'all over the shop'. I don't believe that one should 'draw' any conclusions on the expected performance of a laminated sound board panel based on the shrinkage you observed.</div> <div><br></div> <blockquote type="cite" cite><font face="Arial" size="-1">  Moreover, the greater shrinkage seemed to be in width, rather than in length, with regard to the direction of the grain of the outer veneer.</font></blockquote> <div><br></div> <div>Yes you would expect this, since the draw base was probably of three ply construction with the outer laminates running parallel to the sides, with just one centre lamination running across. The greater shrinkeage therefore would be against the center lamination.</div> <div><br></div> <div>In a solid wood piece the shrinkage would be more pronounced across the grain. In the laminated 3 ply piece the 2 outer plies will be trying to shrink against the 1 inner ply, while the 1 inner ply will be trying to shrink against the long grain of the 2 outer laminations. Clearly, the two outer laminations will have greater success at contracting the long grain of the inner lamination.</div> <div><br></div> <div>Returning to laminated sound boards, I believe that to reduce shrinkage the laminations should be made from quartered material, and the panel should be sealed all over. I have seen pianos where the upper surface of the sound board was coated purely as a cosmetic measure, since the suspended bass bridge had unsealed sound board exposed on the underside of the bride apron. The uncoated area would act as an effective moisture conduit to ensure poor tuning stability in the bass. For the same reason the bridge notching and bridge tops should also be sealed. We mask off the inner rim to sound board gluing area<font color="#0000FF"> (as is common)</font> before spraying the underside of the board, and when installing the board we apply glue to the rib mortices and all around the rib ends<font color="#0000FF"> (completely covering all previously masked areas)</font>. Although our ribs are clear of the mortices at the sides as well as the bottom of the cutout, we apply glue to ensure that the entire sound board area is sealed. The set bolt holes are sealed  also.</div> <div><br></div> <div>As Del mentioned, all laminated panels should be rib crowned. A few on this list have relayed comments from manufacturers who have claimed that RC boards are tonally inferior to CC boards. Often laminated panels have been lumped in with similar criticism. Based on our own experience at this time I do not accept these claims. I would be very surprised if those claimants have actually built a RC laminated board as a comparison<font color="#0000FF"> (I haven't actually built an example of each either, but I've worked on compression crowned boards for almost my entire 29 years working on pianos)</font>. I suspect that their comments are based more on a perceived need to criticise any method which is different to the one they are currently using and have always used.</div> <div><br></div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div><font face="Times New Roman" size="+1" color="#0000FF"><b>OVERS PIANOS - SYDNEY</b></font></div> <div><font color="#000000"><i>   </i></font><font color="#0000FF"><i>Grand Piano Manufacturers</i></font><font color="#000000"><br> _______________________</font></div> <div><font size="-2" color="#000000"><br> </font><font color="#000000">Web http://overspianos.com.au</font></div> <div><font color="#000000">mailto:info@overspianos.com.au<br> _______________________</font></div> </body> </html>