Júlio Galvăo asked:
> I am making a clavichord and I make a mistake gluing the bridge to
> the soundboard. Someone can help me about some method to unglue the
> bridge to correct the mistake? I'm using biological glue.
Fresh animal glue can be released with heat and/or water. One method is
to apply the heat of an ordinary domestic iron to the underside of the
soundboard just under the bridge: with a normal thickness of soundboard,
the heat will penetrate quite quickly (say, in 60 seconds) to the top
side, in sufficient strength to enable you to loosen the joint. But the
method has to be used with great care; the danger is that the heat will
dessicate the wood of the soundboard, and may cause the board to crack
or the soundboard joints to open up. Therefore you have to proceed
carefully and take a number of precautions:
Have a container of hot distilled water handy as well as the hot iron,
which should be about the heat for ironing cotton - ie not so hot that
it will immediately scorch the wood. Have a means of supporting the
board upside down on the bench, with a cut-out for the bridge, but do
not cramp it down as you will need to turn it over frequently as work
proceeds. Mask off the underside of the board except directly under the
bridge with a template made of thin card: heat will, of course,
penetrate this, but the temperature will be less than on the unmasked
places.
Wet the area directly under the bridge: this both helps the transmission
of heat and also protects the wood from dessication. Apply the iron at
first just to a small area under one end of the bridge; count for 60
seconds and then turn the board over, and see if you can *gently* prize
the end of the bridge away from the board with a fairly blunt table
knife - a truly sharp one is just too likely to cause damage. If the
bridge won't come away, repeat until it does. Immediately apply hot
distilled water to the gap under the bridge once it has opened up, using
a clean brush.
Once you have one end of the bridge clear, you can move along the bridge
in stages, using a combination of heat from below and hot water from
above to release the joint of the bridge to the soundboard.
Be gentle and patient, and if you are lucky you will get the bridge off
without damage to bridge or soundboard.
I hope this is clear. Others may have other suggestions.
Incidentally, very old dry glue can be released with alcohol, but I do
not think this method will work will a fairly recently glued joint.
Peter.
--
Peter Bavington
Clavichord Maker
291 Sprowston Mews
LONDON
E7 9AE
www.peter-bavington.co.uk
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