The easy repair or the proper repair?

[Redknuckles]

I have a inexpensive ($300) Yamaha acoustic that's come to me with a buldging, rolling bridge. Looking inside I see the bridge plate has broken through the string pin holes fully side to side. The braces are all still intact and solidly glued, the bridge is still solidly glued with no gapes, so I prefer to leave it alone and installed.

The proper fix I'm guessing is to replace the plate entirely...but is it worth all that trouble? He loves the guitar so I will fix it but I'm wondering if simply making a new bridge plate and glueing it solidly over the original would be enough. I have a $200 budget with a few other tweaks involved so I don't want to put too much time into this.

The belly bulge I'm going to address using the JBL bridge dr., I've never tried this before (I build only custom guitars and do minor repairs) but it seem like the ideal candidate to try. Thoughts?

[Earl49]

I would go with the Plate Mate , after first wicking some glue into the cracks in the original bridge plate. (That crack often happens when someone drives in the bridge pins or oversized pins). http://www.stewmac.com/Luthier_Tools...late_Mate.html

How far you take this repair depends on how bad the bellying / rolling is. Some pictures would help. There may not be a real problem....

[ChrisN]

While I don't understand your guitar's problem or its origin, I've had experience with both Plate Mate (on a Taylor GC for prophylactic bridge plate preservation) and Bridge Doctor (on an old Japanese Martin knock-off for correcting belly bulge and maintaining structural integrity).

The Plate Mate significantly reduced the tone/volume on the Taylor, so I removed and returned it.

The Bridge Doctor (the drilled version, not the pinned one) brought the belly down, and I do not notice any difference in tone/volume, but my relative lack of experience should be kept in mind. Others have said the BD adversely affected tone.

[Redknuckles]

The origin of the original break was cheap, soft wood being used for a bridge plate. It broke/cracked with the grain of the plate, but the plate is still fully glued to the top still. Just now able to effectively work as a hing, allowing the back of the bridge to roll over (under string weight). Measuring the scale, the roll is upto 1/8" twords the nut. Basically the thickness of the saddle blank. affecting the intonation.

The top is plywood and too soft to support the string weight with a compromised plate. Since the crack goes the full length of the plate I don't think the brass plate would be enough to keep the bridge from buckling. That appears to be more for worn out, slipping string holes.

With the string weight removed, the top settles back relieving about 80% of the bulge. It doesn't however do anything for the downward buckle of the top in front of the bridge to the sound hole. That's why I'm going to try the Bridge Dr. as well.

I've heard of the possible tonal issues, but overall reviews say it's worth it. So I think it could be an economic way to repair this otherwise doomed top.

So I guess what I'm thinking is glue a new bridge plate over the cracked original to regain the stiffness lost, and install the Bridge Dr. To correct the bulge that now exists. Remember this is a $300 plywood guitar and a $200 budget. I'm looking for stability and playability till he evolves. This isn't a heirloom yamaha.

[John Arnold]

A bridgeplate break through the pin holes is not going to create top belly, unless the bridge lifts. That is because the bridge itself is a much stiffer, stronger brace than the bridgeplate.
You say that both the bridgeplate and the bridge are firmly glued to the top. Assuming both X-braces are also intact, I would suggest replacing the bridgeplate with a larger one may be the best choice for reducing the belly. For better longitudinal stiffness, the grain in the new bridgeplate can be oriented parallel with the bass side X-brace. That will stiffen the top longitudinally...which is a weakness inherent in a laminated top.
The repair I prefer is a bit more involved. Remove the bridge plate, install a thin spruce patch that fills all the triangular area below the X-crossing, extending it below the bridge about 1". The top is clamped flat while gluing in the spruce patch. This patch is typically about 0.080" thick, with the grain parallel with the top. Then a small maple bridgeplate is installed on top of the patch.
IMHO, the only reason to repair the existing bridgeplate is to prevent the string balls from pulling through. In that case, I would just glue a thin strip of hardwood over the pin holes. Typical dimensions for this are 5/8" wide by 0.075" thick.
I would not install a Bridge Doctor under most circumstances. IMHO, those who say there is no sound penalty from installing one are dreaming.

[redir]

On a $300 dollar guitar I would take John's advice and just glue in a hardwood patch. Removing the plate is a pretty serious operation. In my experience too, a bridge doctor will definitely change the tone. Some people claim that it made their guitar actually sound better. In my limited experience with them that has not been the case.

[mirwa]

Bulging behind the bridge is from excess rotation, this has very little to do with a bridge plate.

Cheap fix for split bridge plate is just patch over.

Fix for excess bridge rotation is check that x brace and other braces haven't broken or failed, make sure the corners of the bridge itself are glued down firmly, make sure saddle projection is not too high, if all these are good then the top has stretched, removebridge steam and clamp the top flat

Steve

[Frank Ford]

A bridgeplate overlay is a logical fix for this kind of situation, and can significantly reduce the "rolling" forward of the bridge if the original plate is considerably wider than the footprint of the bridge but is cracked across either in front or behind the bridge.

I'd go with .10" thick maple, fully as big as the original plate, with the grain oriented PARALLEL to the direction of string pull.

If the original plate is narrow, I'd add a small strip of the same thickness as the plate across the back edge to build it up level so I could use the large overlay I suggested. Plywood tops can crack across the grain right at the back edge of the bridge, and the additional pavement underneath can stabilize things.

Much as you might consider potentially impairing tone with a wide overlay, remember that it's an old plywood top guitar after all, and it's likely to be a cost vs. survival thing. . .

[Redknuckles]

Thank you all for your replays and input.

It sounds like I'm on the right track here for "this" guitars repair. Im going to work on the bridge plate first and see how much strength I can regain, and how much buldging it alleviates. If not enough, I will move on to possibly installing the the Bridge Dr.

[Truckjohn]

Sounds like you are on the right track here.

Instead of a bridge doctor - how about a PTE brace straight across the back edge of the bridge plate.

[murrmac123]

Originally Posted by Truckjohn

Sounds like you are on the right track here.

Instead of a bridge doctor - how about a PTE brace straight across the back edge of the bridge plate.

John, the OP most likely doesn't have the faintest realization what a PMTE (sic) is , so .... to the OP ... Google "PMTE guitar" .

[Mr Fingers]

I'd do the added plate, and if that doesn't bring it to playability and stability, I'd let it go. We all "love" all our guitars, but there's a price tag on everything. I don't really see the point in half-measures. If the owner doesn't have such an attachment that it's a "fix it, period" deal, then I would save my money and put it towards a newer, better guitar. A bulging plywood top... who wants to "fix" that?

[Truckjohn]

Originally Posted by murrmac123

John, the OP most likely doesn't have the faintest realization what a PMTE (sic) is , so .... to the OP ... Google "PMTE guitar" .

. Doesn't everybody know every semi-esoteric "you had to be there on that day" internet luthier forum abbreviation?

For the benefit of the forum...

The PMTE brace stands for Prolux Magic Tone Enhancer brace. Named after Luthier Mario Prolux. The term was coined on another luthier forum probably 10 or 15 years ago... And now - nobody remembers the term except maybe me and Charles...

It's a brace that runs straight across the back of the bridge plate - triangulating the bridge plate in the X brace. It's used to stiffen up a top that is a bit too loose...

As such - it tends to be a good solution where you don't want to add much weight.. Cost is all basically labor of fitting it.

Originally Posted by Truckjohn

..And now - nobody remembers the term except maybe me and Charles...

And me.

I even have one, but oddly enough, not in my Proulx. Regardless, I don't think it's the answer for the OP. The stiffness and weight are enough to make a tonal shift, but has very little effect on structure.

The Bridge Doctor ought never be considered a solution...to anything.

[murrmac123]

Originally Posted by Truckjohn

.
The PMTE brace stands for Prolux Magic Tone Enhancer brace. Named after Luthier Mario Prolux.

Prolux Magic Tone Enhancer does unquestionably have a certain ring to it ...maybe Mario should consider registering "Prolux" as his new brand name ...