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1945 D-18 bridge ( let's get it right the 4th? time!)

The bridge has come off this poor old guitar yet again and has wound up on my bench.

The first 3 poto's are how it sits now, taken by me.

The next 2 photos I acquired from the customer and show the repair that was attempted most recently in progress. It held for about a week.

The luthier who put in this cross grain spruce patch said that the hole in the top from earlier fixes was at least 1/32" deep so I assume at this point the patch is about that thick.

One saving grace is that hide glue was used in the last repair but it seems the spruce (inevitably) split because it terminated right at the point of highest stress at the back of the bridge.

As I see it, there are two possible solutions at this point.

1. Remove the back and double scarf in a piece of spruce that extends well outside the footprint of the bridge. a la Frank Fords method here http://www.frets.com/FretsPages/Luthier/Technique/Guitar/Structural...

  A slightly complicating factor is that the neck was moved south to fix flat intonation by removing material along the entire length of the heel. Leaving the very svelte heel seen in the picture or.

2. Remove the Junk in the "hole" down to sound fibers that cross the footprint intact and add a spruce patch on the inside larger than the bridge outline to carry the rotational load. A la Frank's method here.http://www.frets.com/FretsPages/Luthier/Technique/Guitar/Structural...

 The second option still leaves the issue of action height. A taller saddle = more torque on the bridge. A thicker bridge = tone robbing weight.

I welcome any input from the Fret's.net collective brain as to weighing the invasiveness/cost of a back removal vs. what I see as a second best and slightly distasteful option.

Perhaps a third method has been developed in the years since Frank Ford produced his incredibly valuable essays?

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woops,  more pictures.

More pictures.

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From as far as I can see in the photos through my phone, the prior top patch attempt certainly doesn't look like the hack work I was expecting, but rather a fairly clean professional job. If the joints were solid, it doesn't seem as though the lack of end grain continuity should have resulted in a failure quite so quickly.

That would be a job to disassemble an ponder first hand for a bit. Perhaps when the bridge and spruce patch are fully removed you can get a better view of the joint and why it failed. I fear it may be that even if the joint were well fit and glued, there may be enough loss in top stiffness in the area which allowed the top to flex and leave the stiff bridge/patch system to pull away. Not an easy obstacle to overcome.

I have undercut a bevel in to the back side of similar patches before (though not usually covering the entire footprint), but I don't know if I feel that would offer any advantage in a case like this, as a short bevel wouldn't be enough to stiffen the area. I dread to even suggest this, but it may be worth considering additional support inside the top if bulging of the weakened area seems to be the culprit. If the bridge plate needs removal for other reasons, extending it just enough to stiffen across the joint may help, or perhaps a short brace added along the back side of the plate if it does not otherwise need replacement.

I'm not usually a fan of bracing modifications on nice vintage pieces such as this. In extreme cases where prior damage has left the top weakened or compromised, they are at least options which may deserve consideration, especially considering the more invasive alternatives of back removal and yet more original material being replaced.

Of course disassembly and a more thorough diagnosis of the underlying causes of failure have to come first. Keep us posted, and let us know what you find and decide as you go along.

 

Thanks for taking a look David.

I agree removing the bridge should reveal the plane that failed and will precede any final decision.

I am trying to map out various scenarios for a customer before the ball gets rolling. Back removal is obviously a leap in potential complexity and cost. I don't want to do it unless it's absolutely necessary.

I also agree the work looks well done. I just think it was a flawed plan. It strikes me as identical to a situation I 'm sure many have seen where a finish is scored way too deep and the bridge peels a deep section of top off ripping perfectly along that line. That is to say, I don't think I would try again to raise the bridge on a spruce pad that ends at the back outline.

Although I never saw this guitar under tension, it is not distorted behind the bridge at rest. The x braces are also still glued tight along there length behind the bridge area. Radical distortion often peels those up in my experience. The bridge patch is loose along its front and back edges though, and unfortunately is tucked under the x braces.

If the top is made strong enough from adding material on the inside the action,(already described as low) will have to be brought up through a very thick bridge or a tall saddle leaving thin looking wings to say the least.

 

I guess all that I could add then is that if this job came in to our shop I would write a quote for "blank check". Regardless how well you try to estimate what it may require, there's no telling how many tripwires which you can't see may lie ahead for each one you can. Take the highest possible estimate you could imagine, add 50%, and get authorization for up to that amount before starting.

Of course this often turns potential clients away, and almost more difficult you have to watch the instrument slip away with no way of knowing what it's ultimate fate may be. What initially seems an opportunity to oversee an ensure a proper restoration can quickly become a liability though, if it ends up requiring more work than an optimistic estimate allowed for.

Others may have a different take on this, and hopefully some other experience and approaches that have proven successful in similar cases, though this one seems to face some exceptional challenges with the high neck angle. If it came in to our shop, I'd be seeking input from colleagues just as you are. Hopefully others will chime in on this as well.

Good luck!

Indeed, some jobs that require a high level of skill and have a low level of predictability can also require a "time and materials" repair policy.  For sure, that's the way I'd have to approach this one.  

 I have seen failure in option 2 in my own work and others too frequently to have much faith in it on anything other than bolted down Gibson bridges. One thing to think about also, is what happens when the future repair person (often you) needs to do a bridge reglue ? The top patch will almost certainly need to be replaced if heat is used for removal. Yay warranty work!

 I hate building ships in bottles, but I hate it slightly less than building molds, lining up kerfing and doing the usual touch up where sides and binding disagree. Here are some pics of a ship in the bottle repair. 4 hrs with only light duty profanity. Hope this helps.

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I really appreciate everyone’s input. It is clarifying my thinking.

Ian, I have fit sound post patches in spruce and back button patches in maple on violin family plates flat on the bench in front of me. The work is downright pleasant. Doing it through the sound hole is impressive and something I initially dismissed. Care to elaborate on how you created the hollow? It's hard for me to envision the control required to do this well.

You would have to wonder if the top is still glued to the bridge plate at this time. Also a patch of 1/32nd is not much of a patch. And just mybe the glue that was used to repair it befor was a bit to week.You may just have to take the back off to see just what is going on with this guitar. Seeing that you can't see what it looks like strug up to pitch.Bill...........

 This technique was actually a partial robbery from the sound post patch. I made the piece I wanted to fit in and then used something to transfer high spot markings when I clamped it in. Its been a while, so I'm not sure what I used, around this time I think I was trying snap line chalk.

The previous picture is just a magnet with some sanding paper on it to take down the high spots. The plexi on the top is keep the opposite magnet from falling in the hole or dinging up the top.

I am adding a picture of the prefit peice. Its hard to tell from the picture, but its one item.

Bridge plate is out. 

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 I think I should also add that this was done on a 2 something pyramid bridge and only a section of it. The bridge plate fell out with a firm grip. To do this on a full belly bridge and a tucked bridge plate would require some luthing g-nads of steel. If you are currently trying to make a living or already have a pile of "experimental" projects, I would think a bit before taking this on. Going into the rolodex of excuses when the customer starts calling a month from now sucks.

Thanks Ian, for the photo, explanation, and warning.

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