This idea of adding laminates to the spine of existing
ribs in old pianos can be considered a
"Band-Aid" ( TM ) or an "Overs'-style "I beam rib",
created "in situ".
Take your pick.
For those who choose to consider it the latter, I
offer this proposed methodology:
1) Trace the bridge sweep with a sheet of Mylar (TM)
wide enough to contain it.
2) Feed the Mylar between the back posts, lining the
tracing up with soundboard buttons or other indicators
of where the bridge is on the other side. Mark on the
Mylar (TM) anywhere a rib crosses the bridge sweep
tracing.
3) Obtain a plank wide enough to encompass the
footprint of the bridge sweep ( a 2" x 12" ought to do
it ) and transfer the tracing to it. Drill a 3/8"
hole everywhere a bridge sweep/rib intersection mark
exists. Knock a cheap threded insert ( from weird
parts bins at hardware store ) into each hole, and
thread a 3/8" bolt into it a little.
4 Clamp or screw the plank onto the piano
back/underside, so that when the bolts are turned in
they impinge on the rib spines directly over where
they would intersect with the bridge line on the other
side.
5 ) Make sure the soundboard is firmly secured around
its perimeter with screws, cauls, etc..
6 ) Cut your laminate strips to length and desired
width ( here I am at a loss, having little knowledge
of what sort of stresses exist in various places on
the board, and what sort of
resistance/flexibility/crown/downbearing is preferred
in those areas. As well as little knowledge about what
would make the sturdiest yet most flexible laminate.
Advice solicited. )
Also cut more laminate to proper length for
cauls. Cauls should have few brads along their edges
so they "ride" the laminate below, keeping themselves
and the auxilliary laminate centered side-to-side on
the rib spine. Place auxilliary laminates over rib
spines in proper locations, tape in place and drill
tiny center hole for locating pin ( brad ). Insert
pin.
7 ) Mix up some epoxy with filler ( to make it "non
runny" and spread this over the rib spines, one at a
time, then replace auxilliary laminate and caul, and
screw down bolts to crown out board to desired amount
on other side. ( Advice also sought on this aspect. )
8) Spread "squeeze-out" from glue line so it fills gap
caused by edge of curved rib top and flat axilliary
lamination.
9) Let cure thoroughly. Remove cauls and plank.
If this works as I imagine, the crown will be restored
and supported totally by the laminated rib creation,
and not at all by the board.
As I am pretty busy with my show-business career at
present, it may be a while before I am able to try
this myself. So I encourage others to try it, and
share the results. Perhaps on a crappy old upright
with a collapsed board, withought even re-stringing
it!
Thanks!
Thump
Then --- David Nereson <dnereson@4dv.net> wrote:
>
> This sounds similar to the last resort attempt at
> "re-crowning" old
> boards using the automotive valve spring method,
> where L-brackets are
> fastened to the back posts (or beams) and valve
> springs press on a slat
> of hardwood which rests on the ribs. There is an
> adjusting bolt to
> increase the compression of the valve springs,
> thereby pushing the
> soundboard outwards. I've seen and heard this done
> to mostly school
> studio uprights and it did help. I tried it on an
> old upright which had
> a board with only one crack, still some crown, but
> an annoying buzz.
> The valve springs got rid of the buzz, but the tone
> and sustain were not
> helpeed any. A Steinway owner asked me if the same
> thing could be done
> to increase the sustain and or volume in octaves 6
> and 7 of his model B
> (after I had already exhausted my bag of regulating
> and voicing
> tricks). I was reluctant to do this to a Steinway
> but he was willing to
> try anything. It didn't help. So we tried adding
> brass weights to the
> underside of the bridge. No noticeable results
> there, either.
> So, yeah, you can try it, but don't have high
> hopes. I realize
> these above-mentioned attempts don't include gluing
> any laminates to
> ribs. The springs are held in place by their own
> compression, resting
> on fender washers bolted to the adjusting bolts,
> which in turn are
> bolted to the L-brackets fastened to the back posts.
> The other end of
> the spring rests on the slat which is held against
> the ribs by the
> spring pressure.
> By the way, John Bloch in Denver got the idea of
> doing this from
> Johnny Pullano, long-time tuner for the Denver
> Public Schools. He's the
> one who gave the technical at a PTG meeting at John
> Bloch's shop. It
> has a dramatic effect on some pianos and none on
> others.
> --David Nereson, RPT, Denver
>
>
> _______________________________________________
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>
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