Plate Horn

[Overs Pianos]

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Hi Avery,

>A question for you rebuilder types:
>
>I guess basically it's what is the procedure,=20
>when restringing, to ensure the plate
>horn is snug? Here's what happened:
>
>My apprentice had restrung the plain wire=20
>section of a Yamaha G3. To save a little
>time, I'd pulled up the middle strings for him=20
>with my SAT before he arrived (whole
>step flat) and then he was in the process of pulling in the outside strings=
=2E
>
>I happened to be standing on the bass side and=20
>noticed a piece of gold-painted metal
>lying on the keybed. A little quick looking and=20
>we discovered it was a wedge between
>the horn and the belly (is that what that area's=20
>called?). Well, it wouldn't go in
>but just a little, so I had him start lowering=20
>tension, starting at the bottom of the
>tenor section. After several notes, the wedge=20
>fell out, so I knocked it up again as
>far as it would go. Had to remove the sostenuto=20
>rod to give some "banging" clearance.
>Then, same procedure done again and once more=20
>the wedge fell out. We continued this
>until the wedge was almost all the way in.=20
>Finally, it went all the way up to where
>it'd been originally. Plate screws had been=20
>tightened, BTW. I'm assuming everything is
>OK now. No plate cracks, etc. :-)
>
>I've never had this happen before and am=20
>wondering why it did. Obviously, the plate=20
>moved/flexed a little for this to have happened.=20
>I'd never seen a wedge like this
>before, so didn't think to check it. I don't=20
>know exactly when it fell out: while
>unstringing, pounding in the pins when=20
>restringing, while pulling up the pitch?
>
>Any ideas on what I should have done to prevent this from happening?

There is always a risk of a horn wedge falling=20
out when the pins are pounded in when=20
re-stringing.

The horn has become a rather standard item in=20
contemporary grand piano design. Not all grands=20
have a plate horn, eg. KG series Kawai and=20
B=F6sendorfer grands. However, I believe the horn=20
is a useful way of the improving the structural=20
rigidity of the case/plate assembly. It can=20
slightly improve tuning stability, and may also=20
help the sustaining qualities of an instrument=20
(although the sound board design is by far the=20
most important factor for sustain). While most=20
plates will be capable of withstanding the string=20
tension at pitch, even when the wedge has either=20
been left out or has fallen out during=20
re-stringing, there may be a small risk of some=20
of the lighter plates sustaining damage.

As a general practice, it is a good idea to use=20
tape to hold the wedge in place until sufficient=20
string tension has been applied to hold it. When=20
the wedge is missing and string tension has been=20
applied, it isn't necessary to completely release=20
all string tension before driving the wedge home.=20
Just the minimum tension release required to=20
drive the wedge home will be OK. The plate and=20
pinblock does flex down under tension if the=20
wedge isn't in place, but the flexure will=20
reverse once the wedge is replaced.

I find this design tendency to use just one horn,=20
positioning it at the bass/treble break, along=20
with most if not all of the longitudinal back=20
beams, which also meet at what some magically=20
(and fictitiously) call the 'Tone collector', to=20
be quite a strange design practice/custom. After=20
all, when one considers the belly of a grand=20
piano and the characteristics that we should be=20
aiming for, it is the treble areas where we=20
require the greatest stiffness and rigidity of=20
design, not down in the tenor area. So the=20
traditional placement of the plate to belly=20
bracing might be better placed at the next higher=20
string section break.

With our current Overs 225 piano, it has a=20
traditional cast horn at the bass/treble break.=20
But we also fit additional braces (2) to the top=20
two treble string section breaks. For the Kawi=20
KG5 piano we recently remanufactured and re-named=20
Overs - Kawai, we fitted two additional struts,=20
one at the bass/treble break (since there was no=20
horn in the original design) and one at the next=20
higher break (where the capo section starts). An=20
image of the higher strut can be found at;

http://members.optusnet.com.au/ronovers/overskawai6.jpg

The diameter of the strut is 0.5" (12.7 mm), and=20
the custom-made threaded fitting has a 1/2"=20
thread with 70 mm of thread length in the belly=20
rail. A hardwood block is glued in behind the=20
belly rail sound board support strip, before the=20
sound board is fitted, to provide sufficient wood=20
depth for the 70 mm of thread to be fully engaged=20
with the belly.

I'm a big fan of these plate to belly rail=20
struts. This latest version is quick to make and=20
I think they really help to stiffen the plate=20
against downward flexure at the pin-block area=20
when its subjected to string tension. They must=20
be helping to keep the entire piano stable. We've=20
found that pianos fitted with these struts seem=20
to exhibit improved tuning stability.

>  Any other comments,

We've all been there Avery. You are not alone.

Best,
Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron@overspianos.com.au
_______________________
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