Optimum Bridge height

[Delwin D Fandrich]

> -----Original Message-----
> From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
> Behalf Of David Love
> Sent: February 14, 2004 9:07 AM
> To: Pianotech
> Subject: Re: Optimum Bridge height
>
>
> Okay, let me be more specific.  I'm replacing a soundboard on a Steinway
M.
> I'm replacing the pinblock first.  The original block tapers down
gradually
> so that the treble side is about 1/8" thinner than the bass side.  This
> corresponds to a similar change in original string height from tenor to
> high treble.   Since I am replacing the board and bridges (new caps on old
> root), I don't see any reason to duplicate this pattern exactly or why the
> top end treble shouldn't have the same string height as the tenor.
Unless,
> the added thickness that will result at the treble end of the bridge is of
> any significance.   Am I wrong to ignore this.


I'm assuming you have a tear-down sheet on which you recorded the original
string height. Also on this tear down sheet you recorded the original hammer
bore, right? And you made a note of how much space there was between the
hammershank and the wippen rebound felt with the hammer blow distance set
more-or-less normally?

When fitting the new pinblock I go back and reference these dimensions. If
the string height takes a dip toward the treble I want to know if this
affected the hammer bore. Or, if the hammer bore was "normal" was there an
attempt made to compensate by setting the shanks right down on the rebound
felts. Or were the rebound felts trimmed to make room?

Steinway tended to float the plate all over the place, compensating by
planing the bridge. Normally grand bridge height is somewhere in the 32 to
35 mm (approx. 1.25" to 1.38") range. Plus or minus depending on the piano
maker. Steinway bridges in particular often take a real nosedive in the
treble. Typically down to 28 to 30 mm (1.10" to 1.18") around C88. And down
to the 20 to 25 mm (0.8" to 1.0") range on the rare occasion. Always
expecting the action geometry to take up the slack.

Personally I tend to use the bass end of the pinblock as a general guide and
level the plate in the rim to that height. Unless there is some compelling
reason to do otherwise. This generally raises the treble end of the plate
somewhat. It also leaves the bridge just a bit taller. And makes it possible
to leave the hammer bore a bit more "normal." And allows for a bit of space
between the hammershank and the rebound felt.

Trimming all that height off of the treble bridge does just the opposite of
what you want up there. As does planing down the thickness of the
soundboard. You need some minimum amount of both mass and stiffness to
insure treble sustain. Bridge height and soundboard thickness (both of which
affect the mass and stiffness of the system) contribute to this.

Del