Downbearing

[Erwinspiano@AOL.COM]

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In a message dated 3/29/2002 4:15:04 PM Pacific Standard Time, 
mailinglists@home.se writes:


> 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

      >>>>>>>   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.
> 
> 
> 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? 

>>>>>>>>>>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.

> 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.

>>>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.>>>>>>>>>>>>>>>.

> 
> 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
> 


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