Plate load- piano engineers know this?--how?

[Frank Emerson]

I was involved in one such test.  Many "strain gages" were affixed at strategic locations on the plate.  These gages were about two inches long, and were glued to the surface.  They can detect the slightest tension or compression that might occur at the location where they are attached.  Wires from each gage are connected to a monitor which measures and records changes that occur as the strings are pulled up to tension.  Typically, where one gage is placed on the top of a bar, another was place at the same position, but on the bottom surface.  Where one gage shows a tension strain, the other would typically show compression on the opposite face.  There were some surprises, where the tension and compression stains were showing to be the reverse of what was expected.

These days, similar testing can be done in cyber-space, if you have about $10,000 to spend on the software.  I would expect it would be a six-month project to create 3-D models of every structural component of a piano, defining each component's mass properties, and the terminations and forces applied by each of about 250 strings.  I suspect that the results would be questionable, since the software is designed to be used with metals, plastics, etc., i.e. materials with more predictable reactions to strain than would be the case with components made of wood.  For example, I doubt that the software could factor in the structural strength of a laminated rim, vs. a rim cut to the same shape, with both made from the same species of wood.

Frank Emerson


----- Original Message ----- 
From: 
To: pianotech at ptg.org
Sent: 4/25/2007 6:01:19 AM 
Subject: Plate load- piano engineers know this?--how?


Greetings, 

         Is there any way to view exactly how stringing a piano effects the stress on the harp plate? For example, if you had an unstrung plate and only strung the bass would it have any compressive or tensile stress effect/changes on the high treble section of that plate and visa-versa ; stringing only the high treble...effects bass section of plate?  

          What if you only strung the center, would that have any effect on either bass or treble end or both? How can I get an idea of what are those stresses are and is there any way they can be viewed graphically or measured throughout the casting? 

           Is the only way we know that the stresses are present is by how the piano behaves during a pitch raise? And how do we separate/differentiate what forces are happening in the plate, as opposed to what stresses are absorbed by the bridges and the force they are either releiving or transferring off the plate to themselves or elsewhere in the instrument, i.e. transfered to the sound board and/or case and/or rim? Do piano companies' R&D have a way of testing these things? If so how?

Thanks in advance,
Julia Gottshall
Reading, PA






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