Down bearing

[Daniel Lindholm]

Hi!

It seems like (because of my not-so-good english) that my 
total post have been misunderstood.

The problem isnt to measure the downbearing. There is 
really not any problem at all. I'm just wondering if the 
stringtension can make the soundboard compress through the 
lenght of the piano increasing its crown when strunged.

Just to give you an answer about the downbearing. We 
noticed about 4mm difference when the strings were up to 
tension and when the strings were taken away. We usually 
notice this kind of behavior when we remove the strings. 
Its not a question about IF the downbearing decreases when 
the strings are removed. Its rather a question about how it 
is possible.

So, could it be that the string tension actually do 
compress the cast iron, pushing on the soundboard and thus 
increasing the crown when strung?

When I get back home I'll take some photos where I can draw 
some arrows etc, just to make sure that there are no 
missunderstandings because of my way of explaining (in 
other words my bad english ;)

Best regards,
Daniel Lindholm / Sweden

> David,
> 
> When apparent downbearing is small it is very easy to be 
fooled by these
> commercial 3 feet gauges sold. They will show you a gap 
behind the bridge,
> where it goes in a slant, and you can take that for down 
bearing showing.
> After that, if you use the string method You will see 
that the sting goes in
> a straight line from one end to the other.
> Is it what gives your input unclear ?
> If you move the gauge at every possible place before and 
after the bridge,
> you will have a better figure and see bridge roll, the 
slant on the top of
> the bridge and how it is related to "measured" down 
bearing.
> 
> It is way more precise to have some home made gauges of 
different lengths,
> that can help you to ascertain the existing bridge and 
strings segment
> geometry.
> BTW if your gauge have only 2 feet  I can't see how it 
works
> The measuring gauge with a bubble, while not so accurate 
as we can think,
> can add some information too.
> 
> I feel it is necessary :
> - to learn to use the sound as a DB appreciation (but 
this seems to me a
> long process to learn for a beginner (?))
> - To check crown BEFORE & AFTER unstringing.
> - To use the same method of measure before and after if 
you want to compare
> things and try to deduct something.
> 
> I remember reading some very instructive lectures on 
these subjects in old
> (! 8 years) PUT journal issues, and these are now 
available on the CD ROM
> reprints. at these times it helped me to understand why 
what different
> gauges where showing was different of the real picture.
> 
> Illustrations are needed there.
> 
> Hope and so on .
> 
> There is an old adage that says, the less you know about 
DB and crown, more
> happy you live !
> 
> Much respected by many "restorers" there.
> 
> Another says " In the factory, it worked to put 1mm 
there, 2 there and 3
> there, so it may work the same 40 years after that "
> 
> 
> Regards
> 
> Isaac OLEG
> 
> Francium
> 
> 
> 
> 
> > -----Message d'origine-----
> > De : owner-pianotech@ptg.org [mailto:owner-
pianotech@ptg.org]De la part
> > de Daniel Lindholm
> > Envoyé : samedi 30 mars 2002 23:11
> > À : pianotech@ptg.org
> > Objet : Re: Re: Downbearing
> >
> >
> > Hi David
> >
> > When the strings where on we used one of those metal-
> > thingys with two leveled 'legs'. One leg on the sounding
> > part of the string and one on the part of the string 
that
> > rested on the bridge. If you can wip it, it tells you 
that
> > you got positive downbearing. If it stands firmly on the
> > string, it tells you that you either have zero or 
negative
> > downbearing.
> >
> > As for asking our instructor, we did. He couldnt come up
> > with any better theory than we did with the cast iron 
and
> > soundboard actually getting compressed between the cast
> > iron pins and the tuning pins, increasing the positive 
or
> > negative crown of the soundboard, altering the 
downbearing.
> >
> > I suspect that even though it has alot of negative
> > downbearing right now, when the strings are off, it 
would
> > get back to what it was (positive) before removing the
> > strings, if we restrung it and tuned it.
> >
> > > Hello Daniel -
> > >
> > > At this point I would ask you how you went about 
taking
> > downbearing
> > > measurements.  The rest of your question seems to 
reflect
> > some basic
> > > confusion which might be best addressed by your
> > instructors.
> >
> > Thanks,
> > Daniel Lindholm / Sweden
> >
> >
>