<HTML>In a message dated 3/29/2002 4:15:04 PM Pacific Standard Time, mailinglists@home.se writes: <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">Subj:Downbearing Date:3/29/2002 4:15:04 PM Pacific Standard Time From:<A HREF="mailto:mailinglists@home.se">mailinglists@home.se</A> Reply-to:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A> To:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A> Sent from the Internet                 Daniel</BLOCKQUOTE>       >>>>>>>   More information would be helpful in diagnosing your dilemma but I suspect there is an error perhaps in the way you are measuring bearing. How was that done? It is rather difficult to determine the exact amount of bearing in aged strung pianos. Having been deceived many time myself the only reliable test when minimum bearing and crown is suspected or anticipated is to measure all you wish but the proof of the matter is when the strings come off. If the board rises upward this a positive out come. If it sinks further Hmmm. Since this one has cracks it is likely that the board is completely flat or reversed crowned and that the bearing you were measuring was the result of the strings actually lifting up on the bridge/board fooling you into thinking that there was at least a little bearing. I believe this id why as you let the tension off some of the strings the bearing began to sink.   Also the angle of the top of bridge can fool the best efforts at bearing measurements as that it is usually sloped (hopefully to the rear so as to provide for positive front termination through out most of its life span. You did not mention crown. Did you check it before and then after it was unstrung  with a string across the bottom of the board. I've been fooled by this as well. Also remember you can have crown with no bearing and bearing also with no crown. Many strange conditions exist in piano soundboard systems that were set up carelessly or that have degraded with age. <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px"> Then I formed a second theory about the dissapearing downbearing. Could it be that the strings actually compresses the cast iron and the cast iron compresses the whole soundboard giving it a part of its crown in that way? </BLOCKQUOTE> >>>>>>>>>>Are you using crown and bearing as innerchangeable concepts? Becasuse the above sentence is unclear. And 2o tons of tension is enough to compress most things even a little and the wedged system is a way of allowing the beam super structure  to carry some of the tension load. <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">I cant think of any other way, but I'd like to hear what you all have to say about this since I got little experience in this area. Do you always measure the crown before and after the strings are taken away to make a more accurate calculation of the downbearing when rebuilding instruments? Any tips, theories etc are welcome. I'll be back on thuesday to reply to any comments to this post.</BLOCKQUOTE> >>>I usually don't because if it has ehough when the strings come off I can reuse the board and if not it gets a new one. I honestly put more stock in the way the piano sounds before it's torn down than any physical measurements. For example I've had some amazing sounds come from boards with no crown and minor amounts of bearing so what do I care what the measurements are. I've also had fully crowned 9 ft kawai piano les than ten years old with 10 mm of crown strung and no bearing. I hated the sound. Both in this case were verifiable with measurements. Hope this helps >>>>>>>>>>>>Dale Erwin R.P.T.>>>>>>>>>>>>>>>. <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px"> Note that the downbearing was measured just before and after the strings were taken away on that grand mentioned above and the difference was very big. In some parts we had about 2mm positive downbearing before removing the strings. After we removed the strings we had 1-2mm negative downbearing in some places. Thanks, Daniel Lindholm / Sweden </BLOCKQUOTE> </HTML>