Slanted bridge question

[Delwin D Fandrich]

Isaac OLEG wrote:

> Ron,
>
> We where talking about the reason for the slant in the treble bridge of some
> grand pianos, towards the hitch pin panel i.e; Bösendorfer with a 4 to 8 mm
> slant for 200 mm lenght (according to the specs transmitted by the factory).
> My friend thought this sland is designed push intentionally the sounboard
> (with the pression/ tension of the strings ) in a very small S shape , not
> so important than when the sounboard collapsed because of bridge roll i.e.
> This S shape would allow a more stable shape behind the bridge.
> My personal guess is it have something to do with the downbearing, better
> mechanical rendment, more pressure on the front pins on the bridge, or
> something like that.
> Or would the (curved) bridge be more rigid  with this shape ?

-------------------------------------------------

Isaac,

If the slant you are referring to is what I think it is, it is put there to keep the string's angle of incidence the same at both the speaking side and the back scale side when
the soundboard is loaded.  It is supposed to insure a slight amount of string down pressure along both the front and back edges of the bridge which, hopefully, will keep the
strings from riding up on the bridge pins over time.  You will have to visualize the plate and string assembly in relation to the soundboard and bridge assembly in cross-section
to understand what I mean.

Pianos can be designed so that this slant, or bevel, is not necessary.  The Baldwin grands with their vertical hitches are one example.  If these pianos are assembled correctly
the strings align to the tops of the bridges properly even though the top of the bridge is parallel to the bottom.  Most older piano designs, however, do require some bridge
bevel.

The 'S' shaped soundboard deformation is not a desirable feature.  It is commonly found in compression-crowned soundboards during those parts of the year when humidity is very
high.  Eventually, depending on the exact design of the piano and its soundboard, the soundboard and rib assembly may take on a permanent set in this shape.  I wrote an article
on this subject a couple of years ago in the Piano Technician's Journal that you might want to look at if it is available to you.

Regards,

Del