Removing Aliphatic Glue

[Robert Sherman]

Once in a while a straightforward repair job starts to grow in complexity upon deeper inspection.  An older Martin came in, the owner requesting "a neck set" to deal with rising string action, however it looks like the real issue is not with the neck pitch (there is plenty of back set) but with the top.  The top is sinking in front of the bridge, which seems to be rolling with the torque of the strings over the saddle.  Looks like the bridge patch is failing to stiffen the top between the X braces.

 

But upon inspection, the bridge patch has been replaced; by the squeeze-out I can see that it is held with Titebond.  Aliphetic resin doesn't slip and reconstitute when it is heated like hide glue does.  So now the question is:  can I heat the bridge patch to remove it without causing damage to the adhesion of the adjacent braces and tonebars?  My impression is that its bond will let go at a higher temperature than hide glue so this is trickier than it would have been. 

 

Has anyone been faced with this dilemma?

 

 

 

[Mark Wallace]

Robert,
I believe the temperature required to break the bond is higher for hide glue than for aliphatic resin. I use a metal clamping caul that is a little smaller than the bridge, heating it and working it loose from one side at a time. I heat the plate somewhere beetwen 250 - 300 degrees, clamp it into place, and leave it until the top starts to get very warm to the touch. I have seen quite a few plates fail prematurely simply because of the direction of the grain.

[Robert Sherman]

Thanks Mark, that's a relief. I just want to remove the bridge plate and get the top flat, not pop the braces, and most importantly not change the sound. Next question is how do you get a 300 degree caul maneuvered into place? Do you thread it onto a clamp? Do I have to fabricate this or is there a commercially available version?

[FRANK]

http://www.lmii.com/CartTwo/headerimage/REPAIRBlanketsSPBLseries.jpg CHECK OUT LMII.COM LOOK UP HEATING BLANKETS YOU WILL FIND WHAT YOU ARE LOOKING FORDelete Comment

[FRANK]

i>I would use mdf for the caul because for me it is cheep and i can shape it easily into a caul any shape size and complexity for guitar work

[Robert Sherman]

Can the LMI bridge plate blankets survive the clamping pressure to flatten a warped top?

[FRANK]

yes if you use steel slats like the ones for bending sides they use a blanket for side bending mine has taken a type of clamping pressure i am sure you can find a way Robert