Case separation or delamination question

[Isaac OLEG SIMANOT]

Hello,

I don't understand why this method is still used, and why not in conjunction
with crowned ribs.

Is it because it is more difficult then (with crowned ribs and 4% moist when
gluing) to ascertain a regular , even predictable crown ?

I guess that gluing on crowned ribs only does not build enough internal
tension to the board to be very efficient is not it ?

Just (very) curious.

Regards.

Isaac OLEG



> -----Message d'origine-----
> De : owner-pianotech@ptg.org [mailto:owner-pianotech@ptg.org]De la part
> de Ron Nossaman
> Envoyé : dimanche 31 mars 2002 17:41
> À : pianotech@ptg.org
> Objet : Re: Case separation or delamination question
>
>
>
> >
> > Crowning method was compression, I believe.  I didn't see the
> piano when it
> > first came back, nor before it went out for rebuilding, as this
> preceded my
> > period of employment at the University.  Piano was rebuilt
> during the summer
> > time and, as previously stated, the humidity in this venue does
> hover in the
> > 20% and below region for some part of the winter, at least it
> did so before
> > GWSR  (Global Warming Seasonal Recalibration).    I installed a
> series of
> > crown indicator strings between ribs 3&4, 5&6, 7&8, 9&10, and
> 11&12 (piano
> > has total of 13 ribs).  They are held in place with masking tape, and I
> > retension them and note bearing whenever I tune.  Most
> recently, the numbers
> > I got were: 3&4 - 1/16"; 5&6 - 1/16"; 7&8 - 1/16" or Flat; 9&10
> - Flat; 11&12
> > - Flat.
>
>
> Compression crowning usually involves force drying the panel to
> something in
> the 4%MC range (assuming accurate measurement), and gluing on
> flat ribs. The
> crown comes from the panel expanding with rehydration. In summer
> humidity, it's
> harder to get them dry, and easy to get crown when they
> rehydrate. A soundboard
> panel in a room at 70°F and 20%RH (again, assuming accurate
> measurement), is at
> about 4.5%MC, dropping to 4%MC at 17.5%RH at the same
> temperature. The panel is
> at a moisture content very near that at which it was assembled,
> so it's not
> surprising there isn't much, if any, measurable crown. This is
> one of the major
> problems with this crowning method, and tonal problems in dry
> winter conditions
> are common with this type of board. The tone should improve some
> just by doing
> nothing but waiting for the humidity to go up with warmer weather.
>
>
>
> >
> >  With regard to bearing angles, I am currently revising the
> method I use for
> > measuring downbearing, and so I don't have precise numbers at
> the moment,
> > however, I am virtually positive that the bearing isn't. Why, is that a
> > problem???!!   As far as positive on both sides of the
> bridge...only in my
> > dreams...No, not those, the other ones.
>
>
> That the bearing isn't what? Ideally, you will want both positive
> crown and
> positive overall bearing. Positive bearing on the front of the
> bridge is fairly
> critical, less critical on the back, but overall should be
> positive - but not
> excessive. Yes, knowing the bearing and it's relationship to crown is
> important.
>
>
> >
> > What do you consider to be "some measurable crown"? 1/32"? 1/16"? What?
>
>
> No numbers, just more than none. If gap = true, then crown - else
> not crown.
> With a string stretched rim to rim (or cutoff bar) between ribs,
> If you can see
> a gap between the string and board on both sides of the bridge,
> the crown is
> positive. If you have no gap, or a gap behind the bridge, but
> none in front,
> you may have a problem.
>
> Ron N