rescaling tension

[Delwin D Fandrich]

----- Original Message -----
From: <ANRPiano@AOL.COM>
To: <pianotech@ptg.org>
Sent: June 28, 2000 8:32 PM
Subject: rescaling tension


> I am attempting to rescale a Hazelton 5' grand I had asked you all about
> awhile back.  I am finding I am adding about 1500 pounds of tension by
> getting rid of the very high enharmicity in the bass.

OK.  I'll bite.  Why did you find it necessary to add about 1500 pounds of
tension 'by getting rid of the very high inharmonicity in the bass?'  In the
wrapped string section In is determined primarily by the diameter of the
core wire and that can usually be selected to blend In to fit whatever curve
you want.  (Yes, I know tension and end wraps have an effect as well, but
mostly it's the core diameter.)



> The plate is of pretty
> heavy construction but still 1500 pounds strikes me as a bit much to add.
> Although I thought I once read somewhere that plates are designed to
> withstand 1/3 additional tension than they normally carry.  Would moving
the
> bridge back be a better solution.

Yes, I've read claims like this from time to time as well, but I don't
generally believe them.  Keep in mind that very few piano plates have ever
been 'designed' as we think of the term today.  Drawings were made by
designers and patterns were made by pattern makers to a scantling that
looked good.  If it had enough mass to be acoustically acceptable it was
probably strong enough to support whatever tension the scale had.  Only a
very few companies have ever made any effort to engineer any part of the
piano; plate included.  Remembering, too, that it wasn't until fairly
recently -- as piano history goes -- that the mathematical tools existed to
calculate wrapped string tensions.

You are also assuming that there was any design effort made at all in
developing this plate.  More often than not both the scaling and plate
'design' were simply copied from some other manufacturers piano, changing
and modifying just enough to not get charged with plagiarism.  It was
assumed that the design was strong enough if the pianos being copied did not
break.  If something was lost in the translation and enough of them broke
during production a bit of iron would be added to the weak area and the
problem was solved.  Kind of like is being done today by some of the newer
factories.

Still, with a piano this short you shouldn't have any problem.  Short plates
are generally able to withstand higher tension loads than are their longer
counterparts.  (No point in doing so, of course, unless the soundboard is
really ugly, but that is a decision you will have to make.)  The place to be
especially careful is the X between the bass/tenor break.  This is the
weakest spot in most plates.  Sometimes they were made quite thin,
presumably to accommodate the dampers, sometimes simply by mistake.

Good luck.

Del