20 tons of tension

[Roger Jolly]

Hi Clyde,
          Plate design has come a long way since the post war years, the
average manufacturer has done more with stress analysist. The Schimmel if I
recall has what is termed a full perimeter plate. In other words the outer
struts or webbing form a box, this prevents trapezium distortion from the
in balance of tension due to the cross stringing, but is a cheaper design.
A little more cast iron and no back support. now the draw back. The centre
of gravity has moved back  closer to the rear edge, in a school setting
there is a danger that the piano can easily be flipped over. The other
disadvantage is that the  soundboard liner does not have the same kind of
support as in the more conventional method of manufacture. MY gut instinct
makes me think long term stability may be an issue.
 Most of the tension is taken by the plate in all designs, depending on the
ductility of the cast, rigidity and placement of plate webs ect. will
determine the need for back post, the material used, cross sectional area
and placement. Getting back to the liner and back assy. the average piano
has to bear 1000-1500lbs of down bearing pressure, the sound board is
carrying this load and this is where the liner and back support really
comes into play,as it keeps the perimeter of the board more rigid if well
designed, therefore reflecting more energy back to the centre of the board,
many of the full perimeter plate designs that I have listened to have only
so so sustain qualities. This could be overcome with hard maple or beach
liners, but is not usually the case. You have opened a real can of worms
with this question, so now I will don a flame suit.
Roger



At 10:54 PM 25/08/98 -0400, you wrote:
>Friends:
>
>As I was tuning a late model Schimmel studio piano today I noticed it
>had no back posts, really no back at all that I could see, other than
>the soundboard and ribs.
>
>Which got me to wondering -- how much of the 20 tons of tension is
>usually on the back and how much is on the plate?  Only once before did
>I see a vertical piano without back posts, an old upright.  I also
>remember about 20 years ago a salesman pointing out the rather thick
>back posts on Everett studio pianos as an indication of their high
>quality (I knew much less about pianos then than I do now).  How
>important are those posts really?
>
>Clyde Hollinger (who is getting tired of adding RPT Lititz PA)
>
>
Roger Jolly
Baldwin Yamaha Piano Centre
Saskatoon and Regina
Saskatchewan, Canada.
306-665-0213
Fax 652-0505