Deformed Plywood Top and Plywood Bridge Plate

[Elaine S. Hartstein]

Hello, and thanks in advance for your advice.

What approach would you take to fix a terribly deformed plywood top with a plywood bridge plate?  The bridge lifted over the years, and a pronounced belly formed, leaving the top, under the bridge, quite sloped.  It is not a nice gradual slope.  If one were sledding on the guitar top, one would start at the back of the bridge footprint and slide to the front of the footprint.

The bridge lifted, and was successfully removed. The guitar is one from the 70's, the bridge has two bolts and an adjustable metal insert saddle.  The X brace has come unglued on the treble side near the bridge, where the deformation is the greatest.  The glue used has a white color.

I am quite reluctant to try to remove the bridge plate, as I am afraid the plywood top would come away as well.

Has anyone had success fixing one such as this?

[Bob Garvey]

I am inspired by your tools - I have a spokeshave and stanley 78 blade I could attack to wood (I don't have a torch to bend metal). However, I'm still nervous. Would the aluminum plates from the TJ Thompson Belly reducer be enough to heat the plate? 

My bridge plate and guitar top are both plywood. Does this put me at increased risk for damaging the top? Does anyone know of a video or really great resource (with pictures) for this? I can't find anything. 

[Carl Dickinson]

Elaine,

I'd say nix on the bridge doctor, at least until you string it up and try it out. It took a ladder braced S S Stewart (with a big belly) from having a nice ring to now sounding like a thud. I'm just going to have to take the back off and x-brace it I guess.

[Elaine S. Hartstein]

Thanks, Carl. 

Yes, I will string it up first.  I'm on my third round of heating with moisture and clamping, and things are coming along slowly,  with a bit of improvement each time.

I used the bridge doctor on a couple of other guitars, and it worked out nicely to correct the belly.  I couldn't discern any degradation in the sound, but who knows.  They didn't have the severe deformation that this current one has.  I think the bolts allowed the bridge to stay on, tilt, and act like a lever to deform the top.

Thanks again for the advice.

Cheers,

Elaine

[Roger Häggström]

I would replace/reglue both the bridge plate and the bridge to keep the top flat after heating to flat. Wood has a memory and will probably revert to the previous state after some time with strings at tension. Regluing the bridge and replacing the bridge plate will help a lot. Having the grain in the bridge plate going in the direction of the grain in a solid spruce top will give better resistance against deforming.

[Elaine S. Hartstein]

Thank you!

[Taffy Evans]

Elaine, now, this is a deformed ply top. Angry looking thing, but I loved the challenge.

Taff

[Elaine S. Hartstein]

I wonder what chord they were strumming when that gave way.  Well, at least it saved the time of bridge removal.

Nice job.  Did you inlay spruce under the bridge?

Cheers,

Elaine

[Mark McLean]

Taffy, those are great demonstrations of top repairs.  I was obviously way too pessimistic at the beginning of this conversation when I suggested that it couldn’t be fixed!  

[Taffy Evans]

Hi again, yes I reinforced the bridge plate and inlaid cedar infill.

Mark. You are right really, the job would not have been doable if the customer had not been prepared to pay the ridiculous cost of the repair, the guitar was hardly worth it. Hooray for sentimentality. 

Cheers Taff

[Elaine S. Hartstein]

Taff -

A spectacular job!

Cheers,

Elaine

[Taffy Evans]

Hi bob, any bending of the metal was done cold.

When working on ply plates keep in mind that heat may often soften the glue between the laminations and as you apply your tools you may separate layer after layer of the plate. Messy job. 

I also consider adding a brace behind the back edge of the plate going from X brace leg to x brace leg, once the top is flat. I have to judge each guitar on its merits as far as quality of build, sound, and the care [or not] given by the owner. Also, a loose brace somewhere may have caused the problem in the first place, so I look for that also. Although I can usually hear if a brace is loose.

Good luck Taff