Negative bearing

[Ron Nossaman]

>Measurements were taken with a Lowell component gauge.  Leveled on top of
>the bridge and taken on either side.  The board shows about 1/8" - 3/16"
>crown in the middle of the board when a string is stretched along the long
>rib.  The piano sounds pretty good.  Reasonable power and sustain throughout
>even with old and corroded strings and original hammers.  Bass is a little
>harder to tell because the strings a bit tubby, but overall the board seems
>pretty lively.
>
>> > I'm restringing a Steinway A (6'4") c 1925.  The bearing measurements
>are as
>> > follows:
>> >
>> > Note #           80         60         40        22         10
>> > Front         +.030    +.018    +.012    .000      .000
>> > Back          -.018    -.012     +.006     .000   +.015

So you have a net bearing of about 0.6° at #80, 0.3° at #60, 1° at #40, 0°
at #22, and 0.8° at #10. If you want better numbers without spending any
money, by all means grind the bottom off of the duplexes (belt sander works
well) and try to get a little bearing on the back of the bridge in the
treble. You could also glue veneer or card stock to the bottom to raise
them if you needed to under different circumstances. If you change bearing
by moving the rear duplex bars, you'll de-featurize the piano and mess up
that patented tuned duplex. Can't have that. You can lower the plate
slightly in the low tenor to get some bearing there, which will put a
little more on the bass too. We still don't know what the crown condition
is in the area of the soundboard that goes flat/concave first, which is in
the killer octave, but it's a moot point if the original board is being
retained no matter what.

The back angle is considerably less critical than the front and net
bearing. Ideally, I like to see positive bearing at both the front and back
of the bridge (being supported by positive soundboard crown along the
entire length of the bridge, not just at the long rib, which tells us very
little about the condition of the soundboard), with perhaps a little higher
angle on the front than the back. I've seen a lot of pianos with zero or
slightly negative bearing on the bridge back that didn't sound that bad if
there was positive front and net bearing. 

BTW, bridge roll is soundboard failure.


Ron N