Negative bearing

[David Love]

Ron:

Thank you for your comments.  What is the most effective means to measure
the crown in the killer octave (string?), and what kind of crown would one
look for there.  Since the board is being retained it is a moot point
anyway, more for my own info.

David Love


----- Original Message -----
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: December 01, 2001 7:56 AM
Subject: Re: Negative bearing


> >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
>