Fw: rescaling

[Delwin D Fandrich]

pianoman wrote:
> 
> ----------
> > From: pianoman <pianoman@inlink.com>
> > To: piano tech <pianotech@byu.edu>
> > Subject: rescaling
> > Date: Saturday, September 27, 1997 5:09 PM
> >
> > A few questions for you experienced ones.
> > 1.  What happens if in the rescaling the number of notes of a given size
> > wire changes from an odd to even or vice-versa.  Where does the added hitch
> > pin come from?

It is usually possible to make wire size changes that match the hitch
pin pattern that already exists. The only common exception to this is
down toward the low end of the tenor bridge. Here I will often move or
add hitch pins as necessary to work out a better bass/tenor transition.
Sometime I will switch from tri-chord plain steel strings to bi-chord
wrapped strings in this area. It’s not as difficult as it sounds.


> > 2.  I understand the rule used to be not to change sizes at a plate strut.
> > Is this not necessarily true?

No, not necessarily. It depends on whether or not the original bridge
has an adequate “dog-leg” across the break. If the bridge is correctly
designed and the scale length progression is essentially logarithmic
across the break, it makes no difference. Unfortunately, they often are
not in which case it is necessary to play some real tricks across plate
breaks to come up with a reasonably even scale.


> > 3.  What happens when the plate is too low and the bridge is surface is cut
> > out for the bridge to fit?  How does or does it at all affect the sound as
> > to the size of wire used.  I was under the impression that this was always
> > a bad thing.  Yes-No?

It can be a bad thing though it doesn’t have to be catastrophic. The way
the soundboard is ribbed will have more to do with the sound at this
point than will the stringing scale. See answer #2. The problem with
notching the top of the bridge is that the bridge is essentially a beam
and cutting a notch in the top of a beam weakens it—it makes it less
stiff—and thereby lowers the system impedance at that point. If the
notch is deep enough and if nothing is done with the ribbing to
compensate, there can be a substantial loss of sustain. If the ribbing
is carefully done it can compensate for this somewhat. Bridging the back
of the soundboard at this point can also help, but not as much as good
ribbing.


> > 4.  What measurements on the scale are taken for measurement.  Point of
> > contact in the front and the front bridge pin.  What other measurements are
> > needed?

It depends on what you are after. Basically, I ask for speaking length
(from the center of the bridge pin to the canter of the agraffe, or as
close to the center of the V-bar as you can get), the wire diameters of
the original tenor scale, the diameter of the wrapped string core wire
and the overall diameter of the wrapped strings. I prefer the speaking
lengths to be in millimeters and the wire diameters in inches.


> > 5.  Is the re-scaling programs glorified spreadsheet programs and do all
> > the different programs use the same measurements and give you a choice on
> > inharmonicity and tension?

I don’t know what others use, but mine is a template running under MS
Excel with an attached chart that updates dynamically as each change is
made. Mine uses a couple of routines that are specific to developing new
piano scales and is not for sale. I don’t know anything about any of the
others.


> > 6.  What data do they give you to send away for bass strings?

I return to the technician a printout showing the original scale and the
modified scale. Both with charts. I also send a separate sheet listing
core wire diameters, inner & outer wrap diameters for the mono-chords
and wrap diameters for the bi-chords. These are adjusted to match Mapes
available copper wrap diameters. You’ll still need to send a paper
pattern for the bass strings unless the string winder has an original
scale stick for your particular piano. Mapes has quite a few. I don’t
know about the others. You can also send measurements from the center of
the hitch pin to the start of the wrap and for the wrap length. It’s a
toss-up as to which is better in the long run.

> > 7.  Can you take measurements on a strung piano to see just how good that
> > scale is for that piano and calculate things like amount of inharmonicity
> > and tension level?

Yes you can, but it is a bit difficult to run a tape under the bass
strings and the dampers. It can be done, but you do have to use some
care. It’s a lot easier with two people.

I hope some of this helps. I now rescale every piano that comes through
our shop. No exceptions. I see no reason to put strings on a piano that
I know will not give the best possible performance. I have not found one
original scale among the thousands that I have done that could not be
improved. There might be one someplace, but I’ve not yet found it.

—ddf