Hello Chris and Sterling et allus!
I have been off this thread as I have been out of town for the last
several days...
To answer Chris's question, NO , one does not abrade/plane the bridge
off the soundboard at all.
The problem we face is that wood is an excellent thermal sink, and as
much vertical mass as a bridge has - being 5 to 7 mm high or thereabouts
from treble to bass on a Baroque instrument- its near impossible to wet
and heat the bridge itself and have the heat and moisture pass through
the bridge onto the glue joint and loosen same. You could be there
applying heat and moisture for hours and the minute you remove the iron,
the joint will immediately cool down and the bond will reset before you
can separate the bridge from the top even a little bit !!!
In fact, in this scenario, the only workable solution I know if is that
you must heat a sharpened oil painting palette knife (a REALLY THIN ONE!
) while trying to slip it under a an ear seriously wetted with hot
water where you test to see if the joint is opening with a single edge
razor blade, this in order to start the process.
Then, if you are successful, and can gently slip the palette knife
underneath the ear a little, you add more hot water in front of the
knife ( which you must continually reheat as you work) and as you
gently push the knife down the length of the bridge you must wet and
heat as you go.
.. This is dangerous because the bridge being relatively thick will not
give as the knife is passing underneath. The only thing than can "pull
away" from the underneath of the bridge as the bond is hopefully
loosened, is the top itself.
If the bond is even marginally holding as you are pushing the knife
underneath it you can very easily cause tearout of the moistened top as
I indicated in my first email and believe me , you DON'T want this.
Also its hard to control the water and keep it confined to a small area.
If you want, therefore, to save the bridge you are currently removing, I
believe you really have no choice but to remove the top completely so
you can apply heat and moisture from the BOTTOM of the top directly
under the bridge into the bond area. Here you have several things
working for you.
Thing one :
The top should be around 1.75 to perhaps as much as 1.95 mills here,
NOT 5 to 7 mills thick as is the bridge.
Thing two:
Here the top is MUCH more porous than the bridge and will absorb water
much more freely into the wood so that you can actually affect the bond
directly.
NOW
If you don't need to save the bridge then, it makes sense to plane it
down.
This is done NOT TO REMOVE IT , but to get it as THIN as possible.
In this way, the heat and moisture will penetrate the remainder of the
bridge successfully (now only about 1 mill or so thick) and really
loosen the bond .
Also, if the top is off, you can work it from both top AND bottom as
well and be even more effective in loosening the bond with water and
heat , and also keep the work area small.
Lastly, because the bridge remainder is now very thin, it will also be
flexible (especially being water soaked) and therefore will be much
easier to lift off as the knife passes between it and the top, and will
lessen the chances of pulling up wood from the top .
On 6/15/2012 10:13 PM, Chris Newman wrote:
Question from a newbie with zero experience. Could one laboriously plane/
abrade the bridge off the soundboard?
Chris
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