Strings riding up (was Tuning stability)

[fssturm@unm.edu]

Quoting David Skolnik <davidskolnik@optonline.net>:
> I use a Lowell gauge, but as a determinant for front bearing, I
> measure the 
> smallest possible segment behind the pin to compare with the sounding
> 
> string segment.  As it relates to termination, that's the only
> relevant 
> part. I also slide the gauge to the rear pin to observe the amount of
> 
> curvature  along that segment. It can range from .009" to .050", with
> the 
> .030" range not being unusual.

   This statement got me thinking (always a dangerous thing). I wonder what 
basis there is for our notion that bridge tops should ideally be flat. Other than 
"that's the way I was always taught," which is an attitude based on rote 
education (the main reason products of German and Japanese education 
systems have long been inferior in many ways to Americans, though the "teach 
to the test" attitude that has suddenly reared its nasty head in the US due to the 
so-called "no child left behind" program threatens to rob the American 
educational system of its only true glory: challenge authority. But I digress).
   I am thinking in practical terms: if one chooses (as I do) to resurface the bridge 
top, re-notch and repin, should one make a great effort to get the top back to 
flat? Perhaps not. I will theorize that a curved profile will work just fine, as long 
as, using the string test, a string run from capo or agraffe touches front of notch 
before the rest of the bridge top. In fact, maybe a mild curvature would be better 
theoretically, both for transfer of energy and for durability. Possible, I'm not 
saying it's so.
   How is load transferred through bridge to board? On violin family instruments, 
the bridge top is as close to a point as practically possible. Harpsichords (not 
counting 20th century anachronistic designs like Neupert and Sabathil) have 
the string bearing on a mild point of the bridge, 1 - 2 mm behind the bridge pin 
(with a definite gap between). The flat bridge top is definitely a piano thing, and 
probably mostly by accident of practical considerations (planes make flat 
surfaces). I'm thinking that, although I have believed, like others, that the 
process of resurfacing doesn't affect downbearing, because one is only 
removing material to the bottom of existing grooves, perhaps this isn't really true. 
One may be reducing the loading of the bridge a wee bit by removing the 
curved part in the middle of the bridge.
   Following this general avenue of thought, I wonder what measurement made 
with the downbearing gauge would reflect the reality of deflection and loading 
best, given the reality of string grooves in a bridge top (and a likely curved 
profile). One question that can be addressed is whether and how much the 
string deflects just behind the notch/pin, which will give a notion of whether front 
termination is good. But perhaps a comparison of speaking length level, back 
length level, and measurements with one leg on the middle of the bridge and 
one on speaking length, and another with middle of bridge and back length, 
would give a better picture of how much the string is being deflected/how much 
it is loading the bridge.
   Anyway, a bit of food for thought.
Regards,
Fred Sturm
University of New Mexico