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Adding wood will change the action/sound of the top which may be good or may not be. I think the top must be fine since it follows the deflection Mc usually uses and he says is even stiffer. I think the problem must be with the x braces since he changed the bridge plate with no difference. So the top must be fine, the bridge plate must be fine therefore the only thing left is the braces.

Was finally able to see the pictures with the link. I would be in the camp that thinks maybe the X is not solidly glued in the area beneath the wings of the bridge. You could release string tension and see if you can slip a thin shim between the X and the top in those areas.

I can't think of anything else. No matter how many guitars and years a guy has been at this there is always something new to bite you that you never expected.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

As mentioned in my above post you can check the rotation of the bridge under tension. I mentioned one way but there are lots of low tech ways to check the rotation, also if there is twisting you will see that because one side will rotate more than the other. If the bridge is over rotating or twisting the top is not structurally stiff enough. Checking the rotation provides a definitive definition of the problem, although the cause may still be open to speculation.

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I kind of did that with the new bridge patch, making it slightly bigger. Now I am wondering if a finger brace from the UTB to the X making a triangle behind the bridge will do something. Of course that changes the scope of the project for better or worse who knows till the strings are on.


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I will look into checking the rotation. I have Trevor's book and read about how he does it but I have always felt that the methods used in that 'experiment' would yield results that are not reasonable. Can you really measure 2deg accurately like that within any statistical confidence level? I will at least try it anyway.

I'll check the X-brace again but this will be the 10th time I check to see if they are unglued

I hope they are because that would solve everything!

Regards.

Can you really measure 2deg accurately like that within any statistical confidence level? I will at least try it anyway.

And why not? The method in the book seems quite accurate, using your iPhone is even easier.

A 6" pencil stuck on the face of a bridge will move about .2" with a 2 degree angle. There is a big difference between .2 and .4. You can see it. Trevor's 2 degrees really means some movement but not too much.

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... on the thickness of a top. You discussion of deflection tests and being on the stiff side is an indication that the top should be thick enough but it is not definitive. When finish sanding the area around the bridge is better supported than other areas of the lower bout. As it does not give it is easier to sand more in that area. That is what I think I did. Also a very stiff bit of spruce may call out to go thinner than my comfort level when I normalize for stiffness. Stiffer spruce does not protect against a brace telegraphing through to the top if the top is thin. I run into this more on classical guitars that tend to have thinner tops than steel string guitars.

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Do you mean it's easier to finish sand the top thinner in the area of the bridge patch? I could see that happening but then i would also thing that shining a bright light on the inside would expose the thin spots too. Do you think that is a viable test?

That was my first thought actually but I ruled it out by the light test, I could be wrong. I had made that mistake before and that is why I NEVER use an ROS on the top anymore. In fact I don't really like using those at all anymore really.

I've always thought of telegraphing as being a 'good' thing. All things within reason anyway.

Is ther a tutorial for using a phone to measure rotation? I admit I didn't google it yet...

Put putty on bridge. Put phone in putty. Set your level app to 0 (built in on iPhones), detune guitar, record measurement, reset to zero, tune up guitar, record measurement. It's just that simple...

Just make sure you add enough putty so the phone stays put and doesn't fall onto the top.

If your bridge plate is straight on the back edge you might consider a PMTE (the Proulx Magic Tone Enhancer). It's just a brace with a whimsical name that Mario Proulx came up with. It butts up to the back of the bridge plate and goes between the legs of the X brace. He put them in, I believe, to tighten up things in the bridge area to improve the tone in some cases. I've used one before to repair a soft top that wanted to bow up behind the bridge too much: about 1/4" x 1/4" and butted into the X's.

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Steve Smith
"Music is what feelings sound like"

Hi John,
This is Simon Fay. The issue is most likely with your x-brace and my guess it it's a gluing issue. Based on your soundboard bracing photo, the lower legs of the x-brace are plenty beefy. Even if the wood is very weak, you simply would not expect to see that kind of distortion. It looks like the bridge plate is glued on well and is pulling the top up as a unit but that "unit" completely stops at the edge of the x-brace. This is why I conclude that the x-brace is not mechanically adhered to the top. Even if the brace was unusually weak, you would then expect to see distortion but it should be spread out some rather than appear so abrupt. So it appears that the bracing "system" under the bridge is not working together like it should.


But I do have 1 question for you. You mention deflection testing but that doesn't give us any information. So how thin are we talking here -- What is the thickness of the top? If it is less than 0.09", then you really have to engineer the bridge area to not deform, especially right below the bridge. IF you went ultra thin with a super stiff top (something like 0.080 or under) then your bracing system underneath the bridge is not adequate. You have to really disperse those forces out or you will get massive and abrupt distortion.

Hope that helps.

I don't know what the method in The Book is, but with the guitar neck positioned horizontally, a small laser pointer attached to the bridge pointing horizontally, and a ruler positioned vertically 36" from the laser pointer, a 2 degree rotation of the bridge will move the laser pointer dot 1 1/4" on the ruler . So that's 5/8" per degree which can be measured pretty accurately. You could make it even easier to measure by increasing the distance to the ruler.

That iphone method sounds like a slick idea. I'll have to give that a try. My iphone level only displays in units of 1 degree so the laser pointer on the ruler has higher resolution. It looks like there are some level apps available though that will read out to tenths of a degree .

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The pic above is not the pic of the current guitar. I just quickly grabbed it as an example because I liked the side profile of it for description purposes. Sorry about the confusion. Interestingly the guitar in the pic above deflected twice the amount of the one with the distortion and it's fine but the bracing is indeed different.

Here is a pic of the the same bracing as the top that I am talking about. It's hard to explain but this guitar has been through many iterations. I've literally retooped it twice so far, once because of a dumb error on my part with a slipped router and the other time because I didn't notice there was runout on the top until it was too late and it didn't meet the clients requirements. SO I don't actually have a good pick of the top, but this is the identical bracing pattern as the one in question.

Wow that is a beefy bracing setup. Given a top of average thickness I would not expect anything to move. Has to be an X brace gluing issue. Can’t think of anything else.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I agree, I never got past it happening on both side.

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Yeah, with bracing that heavy, it pretty much has to be a glue problem. And being that it's HHG, and with the failures being symmetrical, it must have been something like too much water in the glue or not enough water in the glue or letting it get too cold before clamping. But that means most likely all of the braces are weakly bonded to the top, and there will be more failures in the summer when the humidity goes up.

Retop.

When you say it's a 'gluing issue' what do you mean? That it is becoming de-laminated? Because I'm tellin' ya, it aint loose at all. I've checked this too many times now, strings on, strings off pushing in, pushing out, and so on. What other issue could there be in gluing? I've been using HHG for a long time now and have yet to see a glue failure. I use small batches of glue that are prepared fresh and so on. Maybe this time there is something wrong but again I cannot stress enough, the braces are glued solid to the top.

I just measured the top thickness at the sound hole and it is .105 inch.

Thanks again for your thoughts.

Freshness is almost never the issue with HHG. I have a plastic squeeze bottle that's been sitting unrefrigerated for years and just tested good again the other day As said, it's the water and temperature where things go wrong.

Get a mirror in there while the strings are on and look at the X joint under the bridge wings. There's no way that much wood can bend that sharply if it's all glued together properly.

A top thickness of 0.105" is nothing unusual and it passed your deflection standards so that doesn't seem like it could be the problem.

Grasping at straws, but how much time elapsed between fitting the bridge to the top and gluing it to the top? Any chance of a change in humidity that could have changed the curvature of the top enough so that the fit was no longer accurate and the top and bridge were forced to fit when gluing them together?

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I like to mix small batches of HHG so that they don't thicken up and have to add water to it. I know it's a common practice but well first of all i never even have enough to let it get too thick and if I did I'd just toss it instead of adding water. I use a gram scale to measure granules and water to mix it up. Of course at this point I cannot say for sure that it is or is not a bad batch of HHG but I do follow best practices using it so I'm setting that aside for now.

It is actually several months between the time I fit the bridge to the unfinished top to hen it goes to get glued down on the top. So that is an interesting point. I am however very strict about RH. I have a couple of good Hygrometers that I calibrate with a psychro dyne twice a year and my shop never goes below 40 and never above 45.

I just checked again last night and unless I am completely blind the X is glued tight. The distorted part is right under the X. It's almost as if the X leans and twists forward it is taking the top with it.

At this point I think I'm going to start doing destructive testing. I suppose there could be a micro crack in the X that I cannot see until it gets exposed with force. IDK

You guys must think I'm crazy I'm going crazy I can tell ya that.

Before you do destructive testing it might be interesting to "sister" the X braces in the area of the ripple and see if that does anything. It may show whether the problem is with the X or elsewhere.

Good idea, I think I will. I might also try that Poulsin brace as was mentioned earlier.

Looking at the photos, again. If the top had been cut next to the outside of the x brace that might result in that distortion (while carving the braces or cleaning glue squeeze out?). Or anything that could make the top weak in that area. Another reach, I'm sure.

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Steve Smith
"Music is what feelings sound like"

Your top is fine. It's not scary thin and is within the normal range of top thicknesses for that size guitar.

Here's one thing that worries me. In the photo shown above, the end of the lower bout braces right behind the bridge patch is clearly showing a gap. Hide glue HATES gaps. The thing about hide glue is that it is easy to use once you get the hang of it but I also think a lot of folks use it when they shouldn't. Titebond is way more forgiving but hide glue requires an absolute perfect mating between the pieces to be glued. If you glue on a radius dish and the braces aren't perfectly aligned, this could cause problems. It is incredibly easy to incorrectly prepare the radius on the bottom of the brace.

Anyway, my point is that if you left a gap there, it is possible there are gaps elsewhere. The only solution here is to take the top off and figure out exactly what is going on. For peace of mind going forward, I would absolutely take this route. I also would make sure the bridge plate extends past the edge of the bridge at least a 1/4" in all locations.

Toonce can you explain what you mean by a gap? And I have to say again that the top above is not the exact one Sorry about that. It is the exact copy of one, in fact it was on this guitar but I chipped it out doing binding and had to re-top it. I do not have a pic of the actual top that is currently glued to it. Again sorry about that confusion.

I think what you might be seeing there is the pencil line. I draw a curved line on the brace to mark the arch out and then use a hand plane to cut the arch in right to the line. Sometimes the line is removed by the plane sometimes not. I never bother to erase the lines but perhaps I should. So as such often times right at the glue joint on my tops you will see a pencil line.

Unless you are seeing something else?