Chickering

[Frank Weston]

>   I am planning on removing a section of soundboard behind the bass
bridge to
> gain gluing/clamping access to top and bottom of the knees/rim joint and
then
> jigging up formed clamping boards...... glue and clamp.
> 
>   Question: Has anyone addressed this particular problem before? If so
how did
> you handle it?  Any thoughts/suggestions?
> Jim Bryant (FL)

This may be blasphemy to some, but I have had great success with rim
repairs using West System 105 resin and 206 hardener.  Here's the secret: 
this epoxy can be made to flow like water by heating it with a hot air gun.
 It will wick into the smallest gaps.  The heat will also release toxic
fumes, so wear a respirator (you may not smell the fumes, but take it from
me you will be affected, and the effect is cumulative).  If you over do the
heating the epoxy will cease to flow and harden immediately, so try a test
piece first to get the idea how things will go.

I place the piano, minus the plate upside down on a trolley.  Try to clean
as much debris out of the cracks as possible.  High pressure air does help.
 Make sure the wood is dry.  I locate all my large clamps and blocks close
at hand.  If the epoxy is likely to flow right through any gaps, I seal the
bottom of the gaps with masking tape.  I then mix up a batch of about an
ounce of epoxy in a paper plate*.  I usually just pour the epoxy over
delaminations in the rim, then heat it with the hot air gun.  The epoxy
will flow and penetrate very fine gaps all the way through from top to
bottom of any rim.  Experiment to develop your own technique.  I place the
clamps on the rim, and tighten them until the epoxy oozes back out of the
crack, and them loosen them a bit to suck more epoxy back in.  Repeat as
you deem necessary.  Finally tighten down all the clamps and allow to cure
overnight.  After cure, you will probably note that the joint line has
sucked in a little more epoxy and is not completely level.  This effect is
mostly cosmetic, but you can fill it with epoxy one more time if you
desire.

What do you do if the gap is in a position that can't be clamped?  Vacuum
bag.  A bag can be built around just about any part of a piano by using
plastic window insulation and caulk.  Use a vending machine pump or an old
refrigerator compressor to draw a vacuum, and draw as much as you can,
usually about 24".  There are tricks to this procedure also, but this note
is getting too long already.

*Paper plates are good because they are cheap, disposable, and because they
allow the epoxy to spread out and slow the exothermic reaction, further,
paper plates make good roller trays if you're in to rolling out epoxy with
a foam roller for gluing, laminating, etc.  But that's another story. 

Frank Weston