This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment -----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 In a message dated 12/20/2002 5:36:27 AM Pacific Standard Time, mcpiano@globetrotter.net writes: . >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? > > Marcel 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 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? The question is if I think ?:-) 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. 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) 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. 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. 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. Peter ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/bf/23/bc/04/attachment.htm ---------------------- multipart/alternative attachment--
This PTG archive page provided courtesy of Moy Piano Service, LLC