Bridgetop Extravaganza Revisited

[Stephen Bellieu]

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    Hi All, =20
Just joined,  first post to this or any other group.  Serendipitous =
timing, just read all the recent bridgetop/ bridgepin posts.  Have a =
1985 Stwy D in the shop for action overhaul and restring.  I thought I =
was noticeing something funny about the bridges but was in denial until =
I started taking all the teardown notes.  The plain wire strings have =
been pounded (seated) into the bridge so that at the edges there is more =
wire diameter below the bridge top than above it.  When viewed from the =
side the wire makes a pronounced curve up onto the bridge and down again =
out the rear making accurate component readings impossible to do from on =
top of the wire.  It was showing negative front bearing until I realized =
what was happening and started using the actual bridgetop as reference.  =
Situation is most severe at capo sections and diminishes down to what =
looks like normal grooves to me under the bass strings.  Deflection in =
strung piano is .5 deg at bottom of low capo,  1-1.5 deg rest of capo =
sweeping up to 2.5 deg at note 88.  There is .250" crown at low capo.  =
(measured from top of board) =20
    Is it possible this condition is due to the quality of the capping =
material?   I usually work on much older instruments.  I have never seen =
string cuts like this.  Also the various pressures have caused dead wood =
to swell up and check here and there around the terminations.  Again I'm =
not used to seeing this.  Inspection of the pins under magnification =
shows the string resided in two distinct locations.   My theory:  Pre- =
and Post Pounding.  There are also a lot of unexplainable nicks on the =
side of the pins.  The pins pull out easily.  No cracks to speak of.  =
This is an institutional piano which has probably been in Southern =
California its whole life.
    What I'm thinking about doing is similar to what Dale Erwin just =
posted.  I've never done the epoxy bridge thing but I'm familiar with =
the nasty stuff. I'm imagining thickening it enough with colloidal =
silica so it won't run down the notches or too much into the holes and =
applying it with a small spatula.  I want to fill those deep grooves (at =
least on the speaking side) and then sand the top flat.  If I put the =
stuff on in the morning can I pare/renotch and redrill at the end of the =
day before it gets too hard and while I can still find the original =
holes?=20
    Looking forward to peoples responses.

    I want to stop using the misnomer "string seating" in favor of wire =
straightening (or something similar)  which is what I do at a low =
lateral angle (around the bridges anyway).  I have never been convinced =
of the need of downward tapping pressure at the bridges.  For some =
reason this is one of the first things new technicians are taught and =
the thought of them going around with little hammers and pounding on =
pianos scares me.  We straighten wire for control of damper and hammer =
contact and for quick stabilization of new strings.  Perhaps having the =
wire come straight out of the bridge helps the string to vibrate in a =
more perpendicular plane even.  I don't really know.  After you take a =
few pianos apart you find that even in a negative bearing situation the =
angled pins hold the string tight to the bridge.  If there is so much =
negative bearing that they don't then no amount of pounding will hold =
them there.  But I guess that is another thread.   Right now I need help =
getting out of this mess.  I have finally accepted I have to pull the =
plate.  So much for the quick restring of a fairly new instrument. =20

Thanks,  Steve Bellieu

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