Decapping bridges with spirit

[Fenton Murray]

Decapping bridges with spiritJohn,
Very nice. I've not seen or heard of this on bridge caps. Would you use this procedure on a pinblock/stretcher joint?

Fenton
  ----- Original Message ----- 
  From: John Delacour 
  To: Pianotech List 
  Sent: Saturday, August 02, 2008 3:07 PM
  Subject: Decapping bridges with spirit


  At 13:30 -0700 2/8/08, Fenton Murray wrote:


      ...I've never come across one yet where it has not been possible to remove the bridge cap intact using alcohol and a suitable selection of knives and rods...


    John,
    Would you mind describing this procedure with a little more detail, even photos.


  If I have time in the next few days I'll set up some photos, since I brought in a piano yesterday that is for the bonfire and I'll be salvaging the key-bottom to make a trolley, so everything will be in position.


  In the meantime here's a picture of a bass bridge cap I removed a few weeks ago.  I think the job took about 15 minutes and there is no damage to bridge or cap.


  The part that is usually slightly more tricky is getting the split started, but it's really more a question of patience than feasibility.  Once you have the beginnings of a split, the rest is plain sailing because the spirit (ie. alcohol) travels by capillary action.  To start the split in this case I would have aligned the edge of a very sharp knife with the glue line at the end of the bridge and tapped it in a little way. I then put a few drops of spirit on the top of the knife, wait a few moments and tap the knife in a little further and continue patiently adding spirit until the initial parting takes place.







  Once this has happened it is just a question of maintaining upward pressure on that part of the cap that has already detached itself (using suitable knives, chisels, awls etc.) and feeding spirit into the split.  As the spirit works -- and it works fast -- you hear a reassuring cracking sound as the glue gives way and can then raise the end of the cap a little further to provide the same pressure, feed in more spirit and so on.


  This week I used the same method to remove 24 glued-in rosewood panel mouldings from two upright top doors in order to polish them and allow the main door panel to be French-polished.  Each set took about 20 minutes to remove, and there is no damage.  In this case I started of the removal of each mounding by driving an awl between the end of the moulding and the seating in order to provide pressure and give the spirit an entrance.  Of course these mouldings were not as firmly glued as is a bridge cap, so things went slightly faster, but the method works for anything.


  As I've said, I work on pianos which are glued with animal glues, but I suspect that at least some synthetic glues would also respond.


  JD





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