Hitch pin adjustment

[Delwin D Fandrich]

Serge Harel wrote:
> 
> 
> Dear M. Fandrich and list members
> 
> I got an 10 years old S&S D in my shop to restring.
> The crown is is 4mm  at 50% of humidity.
> And there is a lot of downbearing 3 to 4 degrees on the long bridge and
> 2 degres at the E20 on the bass bridge to 0.5 degrees at the A1.
> 
> Do you think it's excessive?
> 
> This piano is one of the best concert grand in town.
> 
> Serge Harel

Serge,

You don't say for sure, but I'm assuming that the string deflection
angles are taken with the piano strung and at pitch. Also, I can't
speculate on the sound of a piano I can't see and hear, but there has to
be some penalty for having this much string loading on the soundboard.  

Let's assume that you have a piano string with a speaking length of 670
mm and a back scale length of 190 mm (this example is not taken from a
Steinway D, but is a typical note taken from the middle of the tenor
section a large piano) and let's assume that this string has a
deflection over the bridge of 4.0 degrees. (This is the downbearing
angle you say this piano has.) Now strike an imaginary line from the
hitch pin (or back bearing bar) to the agraffe; i.e., a line passing
through the bridge, and not over it. Now measure straight down from the
top of the bridge to this imaginary line. The distance will be 10.3 mm.
At 3.0 degrees deflection the distance will be 7.7 mm, at 2.0 degrees it
will be 5.2 mm, and at 1.0 degree it will be 2.6 mm. 

If the soundboard on this piano actually does have a positive crown of
4.0 mm today, it sure won't for very long. It will be flat in just a few
more years and will end up around minus 4.0 mm a few years after that
due to the extremely high downforce of the strings against the bridge.
No soundboard can stand that much stress for long without giving up in
dismay.

Yes, I'd say that much string deflection is excessive. At this point in
the scale 2.0 degrees would be excessive. Eventually even 2.0 degrees
would probably drive the board into a reverse crown.

If this piano were in my shop, I'd want the answers to a couple of
questions:
  1)  Why is the piano going to be restrung?
  2)  Are you sure you've correctly measured string deflection?
  3)  Are there any clues as to why the string deflection is so high?
  4)  Has any major work been done to the piano since it left the
factory? 
  5)  Is there any evidence that the nosebolts have been used to
"adjust" the downbearing?
  6)  What does the surface of the soundboard look like? Has there been
any damage to the soundboard as a result of having this much pressure on
it to date?

Well, you get the idea. Yes, I'd suggest decreasing the string
deflection just a bit. Good luck!

ddf