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>>There was some list discussion about sound board presses recently. I
>>got the first image of my vacuum sound board laminating press
>>prepared for the web site yesterday. The image below shows the press,
>>with a test strip of sound board panel and one rib being pressed.
>>
>>http://overspianos.com.au/vacpress.jpg
>>
>>The press is 6' x 8'
>>(1800mm x 2400 mm). The vacuum pump is a Becker 3ph 2 hp unit.
>>
>>A cutaway of the pump can be seen at;
>>
>>http://www.becker-international.com/en_z010.html
>>
>>It can pump 28 cfm when unrestricted and the vacuum can be adjusted
>>from 1.5 psi to 12 psi. (12 psi will yield a hold-down pressure of
>>around 0.75 tons/square foot - or 0.8 atmospheres). We use the
>>minimum 1.5 psi vacuum for gluing the panel to the ribs. The vacuum
>>diaphragm is a fibreglass reinforced vinyl, fitted to a lightweight
>>RHS frame which can be lifted on and off the table with ease. The
>>vacuum is delivered from the pump to the the table using the RHS
>>frame as a vacuum plenum. A series of holes on the inner edge of the
>>RHS allow the air to be evacuated from around the perimeter of the
>>table. Apart from its use as a sound board assembly table, the press
>>is also very useful for gluing veneer to panels. We will also use it
>>for the manufacture of the laminated sound board panels which we are
>>using for our own piano. By the way, the poser in the image is my
>>Rottweiler 'Harry'. He likes to fossick around the workshop chewing
>>the odd sound board off-cut.
>>
>>Best,
>>Ron O.
>--
>
>Ron,
>
>I also meant to comment on this and got this out of the archives as
>well. At some point you mentioned, either on this list or to me
>personally, that you were still undecided about whether to use solid
>boards or laminated boards in your pianos and that you were going to
>do some further experimentation.
Phil,
Yes, we discussed this at Reno.
> Since you mention the vacuum press for making laminated
>soundboards can I assume you've decided that laminated soundboards
>are superior to solid boards for giving the results that you want?
>
>Phil Ford
Yes, I now believe the laminated panel is vastly superior in
performance to the solid panel. The vacuum press is for gluing up
laminated sound board panels, and other panels which we might wish to
veneer, and for gluing the rib set to the sound board panel. Since
our ribs are flat on the bottom and machined on the top surface to
the radius at which we wish to crown the board, the ribs can be set
out on the flat surface of the vacuum press with the panel pulled
down onto them by the vacuum diaphragm. Using this system, we don't
need individual gluing cauls for different pianos, since the rib
profile determines the crown and the ribs sit directly on the flat
board (there is a plywood panel between the ribs and the press, to
which the ribs are screwed at the ends - the screwed down section is
machined away afterwards when ribs are feathered). We are using an
ordinary short-knap paint roller for applying the glue (Titebond) to
the ribs before placing the panel on top. After a little experience
you get used to applying just the right amount of glue so that there
is no squeeze out. One other matter, which is most important, is that
the panel must be lowered directly onto the ribs without slewing the
panel sideways during the process. Otherwise the panel will get an
unsightly glue smear, and glue will be lost from between the adjacent
gluing surfaces. To facilitate lowering the panel vertically onto the
ribs, I made up two telescopic guide pins which are fitted into the
rib-mounting plywood panel. The two guides are positioned such that
the panel practically balances on them. The telescopic guide pins
extend upwards 25 mm clear of the rib set (with internal piano wire
springs of course) when there is no panel weighing them down. After
applying glue to the ribs and quickly removing the panel from the
conditioning box, it is placed onto the telescopic guide pins, then
the weight of the panel compresses the guide pins down until it rests
on the rib set. That's it, just placing the diaphragm over the whole
'shabang' and turning the pump on is all that's left to do.
After much consideration, I am now of the view that I probably won't
ever use a solid sound board panel. I am not referring here to the
'el-cheapo' laminated panels which are common in the bottom end
instruments, which have given laminated panels a bad reputation
(although one low ender recently gave up laminated panels - which
seemed to have some redeeming qualities - in favour of traditional
solid panels, which like so many other traditional solid panels, just
go flat even before the piano makes it to the showroom). I am
referring to carefully built laminated panels, where each laminate is
constructed as if it were to be a first quality solid sound board
panel, but 1/3 the nominal thickness, ie. properly quartered boards
shot and joined properly with no air gaps. Three of these 2.5 mm
thick panels make up one laminated panel (we sand the middle laminate
to 2.5 and the outers to 2.8 - this allows for some final sanding
after they are glued together).
There are several compelling reasons why I believe the laminated
panel is superior to the solid version. Firstly, the solid panel is
more prone to self destruct with the hygroscopic changes which
encourage compression/tension set. Have you ever wondered why some
sound boards check in certain boards of the panel, while other boards
in the same panel remain without cracks? Well this problem is
probably due to the variation in strength and density of the various
boards which make up a panel. When the panel is subjected to humidity
variations it tries to expand or contract. When it tries to expand
the weaker boards in the panel will tend to crush or compression set
more quickly so that when the panel dehydrates under drier
conditions, it will be the weaker and lighter boards which tend to be
the first to to be pulled apart. If the panel is cross laminated, the
cross laminated long grain will force the panel to share the
expansion and contraction more evenly. This is one reason why you
just don't see compression ridges in a properly laminated panel, and
it is also the reason why cracks in a laminated panel are almost
unheard of.
So the laminated panel, with cross grain which is much less prone to
change dimension with hygroscopic variations, will result in a panel
which is more stable regarding tuning stability. After having some
experience with laminated panels, and after finding that there is
almost no shrinkage of the panel when dried down to 6% moisture
content, I would doubt if CC boards could be made using laminated
panels, since to achieve any noticeable crown, one would almost
certainly have to crown the ribs.
We are running the top and bottom laminates in the same direction as
for a traditional solid panel, ie. along the line of the long bridge,
with the middle laminate at 90 degrees and parallel to the sound
board ribs. While some might see this as a disadvantage, since 1/3 of
the panel thickness is oriented with the ribs, I don't see any
problems associated with it. Certainly the laminated panel is
somewhat more flexible along the line of the long bridge, and stiffer
parallel to the ribs, but the long bridge if adequately dimensioned
will be more than capable of ensuring the whole assembly maintains
its togetherness. With a rib crowned board, the most important job
the panel has do is to ensure that air doesn't leak past the ribs
when they go up and down. The laminated panel will do this without
encouraging variations in crown as moisture levels change.
Ron O.
--
OVERS PIANOS - SYDNEY
Grand Piano Manufacturers
_______________________
Web http://overspianos.com.au
mailto:ron@overspianos.com.au
_______________________
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