Down bearing

[Isaac OLEG SIMANOT]

Keith,

In my understanding, when the board goes flat, if the stings are pulling the
bridge up, by reaction, the front of the bridge will go down (bridge roll) .
I hardly imagine how it can go high enough to add visible DB at the front
pin.

What I have seen is that the pressure place moves slowly from the first
front third of the bridge when in a normal configuration, to the rear of the
bridge, to the point apparent DB remains only visible a t the rear pins,
giving that particular sound without much density and clearness.

Any further explanation I will appreciate.

Regards.

Isaac OLEG

> -----Message d'origine-----
> De : owner-pianotech@ptg.org [mailto:owner-pianotech@ptg.org]De la part
> de Keith Roberts
> Envoyé : mercredi 3 avril 2002 20:01
> À : pianotech@ptg.org
> Objet : Re: RE: Re: Down bearing
>
>
> Daniel,
> No, I don't think we misunderstood you. You said the board pulled
> away from
> the strings as you destrung the piano. The bridge has to be
> thicker than the
> distance between the string and the sound board to have
> downbearing. In your
> case, because of the slant(downward slope towards the hitch pin) of the
> bridge, the rear bridge pin pulls the bridge upwards causing the front pin
> to rise higher than the string plane. Yes it appears normal to the gauge.
> Pay attention to Dale Erwins post on stringing the board from underneath
> before and after.
> No, the plate does not flex enough to change the crown of the
> soundboard or
> downbearing. Nose bolts are supposed to stop the plate from
> flexing to much
> and cracking. Sometimes they are needed but are never used to distort the
> plate to affect bearing.
> Boards are crowned by arcing (cutting not bending) the ribs to a
> 40 to 60 ft
> radius or drying the board more than normal for gluing and the swelling of
> the board after makes the crown. Or both.
> Check the list archives for discussions on soundboards.
> Keith R
> ----- Original Message -----
> From: "Daniel Lindholm" <mailinglists@home.se>
> To: <pianotech@ptg.org>
> Sent: Sunday, March 31, 2002 2:40 PM
> Subject: Re: RE: Re: Down bearing
>
>
> > 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
> > > >
> > > >
> > >
> >
> >
> >
>
>