Leveling of strings

[Delwin D Fandrich]

Maxpiano@aol.com wrote:
> 
> In a message dated 97-08-01 15:51:28 EDT, Michael writes:
> 
> <<
>  In the case of non-level strings, the wave shape due to the contact of the
>  hammer's twisting while contacting would certainly give a more out of the
>  ordinary shape to the wave on the string.
>   >>
> Thanks for the insight.



> 
> 3.  What if the mass of the hammer/shank combination is off center such that,
> even though the strings are level and the initial strike is square,  the
> hammer wobbles before leaving contact with the string; would this not also
> produce unwanted sounds?  I can envision a scenario where either the hammer
> does not rise 90 degrees to the plane formed by the level strings, or it does
> rise 90 degrees but the mass is not squarely behind the impact.  I hope I
> make myself clear.
> 
> Bill Maxim, RPT



Bill, 

Therein lies the problem, of course. Hammers do not travel in a straight
line (or more accurately, arc) to the string(s). 

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                          !!! WARNING !!!
The following may be too mind numbing for a Saturday morning. If you
choose to ignore this warning, then get a good, strong cup of coffee, a
muffin and proceed on at your own risk.
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Wood is often regarded as a homogeneous material when in fact it is
heterogeneous. A material is homogeneous if it has a similar composition
throughout its section. The material forming a marshmallow homogeneous.
Most un-reinforced plastics and metals are homogeneous materials. A
heterogeneous material, on the other hand, has a composition that varies
through its cross-section. In a piece of wood as long and as slender as
a hammershank we must remember that it is not homogeneous, but
heterogeneous. Its composition does vary throughout its section.

In a member of some size—a piano leg, for example—wood can be treated as
if it were homogeneous. It is so large and the wood grain is so fine
that the variations of density and stiffness among the individual grain
lines can be averaged together and treated as if the material were a
uniform solid. However, in a member as small as a hammer shank the
heterogeneous character of wood must be considered. The grain of the
wood used to make hammershanks runs more or less lengthwise to the
central axis of the hammershank, but both the grain angle and the
density and stiffness of the grain varies from one piece of wood to the
next. The density and stiffness of the latewood layer is greater than
that of the earlywood layer. Often a hammershank will be made up of a
piece of wood having only one earlywood layer and one latewood layer.
Even if there are more, if they are not symmetrically positioned—and it
would truly be serendipitous if they were—the hammershank will not be
uniformly stiff throughout its section. 

Add to this the problem that the bore of the hammer is rarely exactly in
line with the hammers center of mass and even if it were it is unlikely
that the hammer will be hung with its center of gravity exactly in line
with the arc of the hammershank. 

Yes, there is a point to all of the above ramblings. When the jack
applies force to the hammershank knuckle—Is the jack aligned exactly to
the center of the knuckle?—and forces the hammershank to begin moving
through its arc—Do both action center felts have exactly the same
density and resiliency?—and the hammer begins its path toward the
strings IT DOES NOT TRAVEL IN A STRAIGHT LINE, OR ARC. The hammershank
bends and twists and the hammer wobbles and flops around like crazy.
There is no way of predicting exactly where the point of impact on the
tip of the hammer will be. Oh, certainly, it time it will average out
and eventually grooves will form on the striking surface of the hammer
just as grooves ultimately form on the highways from the millions of
truck tires that pass over them. But there is a bit of uncertainty with
each specific hammer blow. 

Therein lies my problem with the practice of trying to “fine-shape” each
hammer to fit slightly out of level strings. If you gently pull the
hammer up to contact the strings and pluck each string of the unison to
find any that are “open” and then file the hammer to match the strings
what guarantee do you have that the hammer will actually strike the
strings in that same spot? None at all, actually. 

Like all aspects of piano service, this is one more that can be—has
been—taken to its illogical extreme. If no string leveling has been done
since the piano was strung, then do it. Shouldn’t take more than about
ten minutes. If the hammers haven’t been filed smooth and square, then
do it. Shouldn’t take more than an hour or so (maybe a bit more if
you’re slow like me). But, if the hammers are filed reasonably clean and
square, and if the strings are reasonably level, and if the agraffes (or
V-bar) are properly machined, you’re simply not going to have a problem
here. Get on with tuning the piano, fix that squeaky pedal and get on
with life.

ddf


(By the way, in another post someone asked about string leveling on
vertical pianos:
It’s usually not necessary and there is a reason. Vertical pianos are
capable of inherently better upper string termination, the reasons for
which are too lengthy to go into here. But I did write about this at
some length a year or so ago in one of my Journal articles and which. If
anyone is interested and can’t find the appropriate article, let me know
and I’ll try to track down which issue it was in.)