<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; = charset=us-ascii"> <TITLE>Bericht</TITLE> <META content="MSHTML 6.00.2722.900" name=GENERATOR></HEAD> <BODY> <DIV> </DIV> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px"> <DIV></DIV> <DIV class=OutlookMessageHeader lang=nl dir=ltr = align=left>-----Oorspronkelijk bericht----- Van: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] Namens = Erwinspiano@aol.com Verzonden: vrijdag 20 december 2002 17:08 Aan: pianotech@ptg.org Onderwerp: Re: = Soundboard Clamping for Downbearing </DIV>In a = message dated 12/20/2002 5:36:27 AM Pacific Standard Time, mcpiano@globetrotter.net writes: <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">. >Marcel wrote: > >>To me, after the crowning process, the = board should not >be dried again. I >>think that high = temperature MIGHT affect the glue >hardness and cause = crown >>collapse (a little at least). > >Please explain what you mean by = "high temperature". And why >would it be used? > ></BLOCKQUOTE> <DIV>          &n= bsp;           &nb= sp;   = Marcel           &nb= sp;           &nbs= p;  I often keep the boards in the hotbox after they are pressed at what = ever temp needed to keep the rh between30 and 40% which is often 70 to 80  = degrees in a high humidity sesaon. However it doesn't hurt any thing if the = board is dried down to it's pre-ribbed state of say 90 degrees and 25 to 30% = R.H. Even if you glued the board to the case in that dry it will still regain = whatever crown was lost due to being redried when it gains moisture = content.Besides whatever crown there is due to the ribs being crowned is more than = ample, even in the driest conditions. Purely =            &nb= sp; Compression crowned panels will suffer greater losses of crown under = the conditons described above and will have very little or none if they = were'nt carefully dried to about 4.5% EMC before ribbing instead of what Peter = posted earlier describing basically no drying at all. Peter, what were you thinking? </DIV> <DIV> </DIV> <DIV>The question is if I think ?:-)</DIV> <DIV> </DIV= > <DIV>1)I have experienced now = that compression crowned boards loose very much crown by unstressing them; = so if you want to work this method you should carefully dry the panel so the = wood will swell and taking crown by the change of humidity.  And = you also have to "overbend" the ribs to keep some crown after a few days, weeks.  That's the only way to be shure to keep some crown.</DIV> <DIV>2)Using compression crown = and drying the (in my case not dried before gluing on the ribs)board before = installing it in the piano will present the risc of having negative crown (which is the = case for the moment with me) and cracks (in extreme conditions).  = Problems then are : how can one attach the bridges to the board? By puching = more you also bend the board in the direction it may not bend.  If you = have crown and you puch with more force, the board is going flatter which will = allow to have the bridge full contact with its complete surface.  (Of = coarse you can puch that much so you will puch through the board, but I think = no-one will take that risc)</DIV> <DIV> </DIV= > <DIV>So if you want to know, I'm = going to restart, ie taking of the ribs whith a plane and placing new crowned = ones, drying the board and the ribs carefully to a MC as low as possible and = then gluing and clamping them = together.</DIV> <DIV>The "only" problem I still = have: how much crown should I give to the beams of my press: none, and arc of = +/-18m for the longest ones and +/-15 for the shortest ones, (like the ribs are precrowned),  +  for having  more  crown at the = end?  (How much should one have with a new board anyway?) Can = somebody me tell that please?  I only know that the uncrowned beams of my = press give about one cm of crown when I'm blowing the hoses. </DIV> <DIV> </DIV= > <DIV> </DIV= > <DIV>I also want to thank all of = you who have discussed this item.  Do not think I feel blamed but it was hard = at some points.  I have learned my lesson and made my conclusions = that you can read above.  But I think this was the money I have to pay = for.  And after all, in doing 15 years of restoration of piano's, I have = only to restart 2 times a job.  I think that's not bad.  And also, = making soundboards, I love it more and = more.</DIV> <DIV> </DIV= > <DIV>Peter</DIV>= <DIV>  </DIV></= BLOCKQUOTE></BODY></HTML>