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All the photos are visible to me again now.

For whatever it's worth, my middle size guitar body has 1/4" wide x-braces at 98 degrees without problems.

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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

So let's look at what we do know. You said the distortion was less on the bass side. When I look at the picture of the top I see that the plate extends farther on the bass side than it does on the treble.

What that makes me think is that the bass side is less because the plate is taking up some of the slack that the brace apparently is not. So one thing you could try is extending the ears of the plate further on the treble side and seeing if that makes much difference.

Is there any distortion near the edge of the top on either side?

What kind of glue did you use on this build?

Sorry Dan, I'm dyslexic. Even though I reread what I write I often times don't get it right. I fixed it in my OP. But it's worse on the bass side and not as bad on treble.

So that brings us full circle.

Assuming you've been inside with a mirror to verify interior structures? Seems like that much distortion should, in that area, be easy to pinpoint with some obvious failure. Of course nothing obvious or you wouldn't be posting but seems like the culprit should be visible upon a close visual interior examination.

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Thank You and Best To All

I'm 211% certain that that picture is loading!

Do you do any deflection testing on the X braces or on the top after it is braced? How about flexing it as you're carving? Did everything feel normal stiffness?

New username, same ole Pat Mac

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Pat

Do you have a shot of the braced top before it went on the guitar? I've seen this before, but usually only when a builder chooses to scallop the bracing on the upper arms of the X-brace.

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For the times they are a changin'

- Bob Dylan

There is no scalloping. Forgot to mention I used HHG.

After further looking, the distortion I am almost certain is right under the X-Brace adjacent to the bridge patch on the bass side. I have triple checked with bright lights and mirrors and everything is solid. I'm almost convinced now that there is just some inherent weakness in the X-Brace and that as the bridge rotates that part of the X is twisting, it's still glued so it's twisting the top with it.

Of course that doesn't explain the treble side. But that is a lot less harmful. And on that side the distortion is away from the bride and almost right under where the UTB and the finger brace meets.

Your original post suggests you want to learn from this and never let it happen again but am curious what you might do differently next time? I'm not sure anyone can point to a definitive technique that you may have implemented 'wrong' or even improve upon so am wondering what you might do differently? My apologies in that I cannot offer any expert advice but have so much to learn and your expertise is greatly appreciated.

Thank you

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Thank You and Best To All

Did the two x-braces come from the same brace blank? If there was a defect in the brace blank and the two braces were made from adjacent parts of the blank, they could both have the defect.

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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

Still no pics for me to see, so I have to flee, and let it be, and have a tea

Yeah exactly! That's the hard part. This is my 60th guitar and I have NEVER seen anything like it.




Yes they dad and this is exactly what I am beginning to wonder too. Interestingly this brace wood came from the Gurion shop before the fire, so it was cut in the early 70's or even older. You'd think it would be well seasoned

It's the damnest thing, Google photo's. I make sure the link works in a private window and I swear they change the links. Anyway I tried again.

Since your glue is HHG could you take out the X bracing and replace it with different stock and make the bracing a little taller? I think Lowden uses taller braces to good effect.

Google has a share link oprion so for thos ewho cannot see the photo's this should work:

https://photos.app.goo.gl/WLed2qXFU7uzhENG8

I'd like to help, but I don't see the pics.

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formerly known around here as burbank
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http://www.patfosterguitars.com

Even with the link I posted above Pat?

Hi

I had a similar experience a couple of years ago. When I strung up the guitar the treble side below the bridge deflected. The deflection was slightly more to the lower bout than yours. I checked the braces with my hand and was sure they were glued down tight. The deflection was almost gone when I loosened the strings so that I could get my hand in. Tighten the strings and the deflection was back. Finally found the problem when I used a mirror and light with the strings at tune. The X brace I thought was glued tight, wasn't. You have said you are sure the braces are glued tight but did you check them with the strings at tune? If you have, please disregard this post, but if you haven't - give it a look. - Mike G

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guitarsbygiltzow.com

Hey jfmckenna, I've had (what looks like) a a similar distortion. More like a pucker than bridge rotation? in My case it was from cross grain shrinkage of the bridge glue joint. If its like mine, I suspect an unusual expansion/contraction cycle involving the laminated bridge plate when the bridge was glued up. was the pucker evident before stringing? Have you used that same grain direction Spruce patch before?

I have done laminated bridge patches before. In fact I thought using 'plywood' was more common but perhaps not. Anyway since the time I last posted I removed and replaced the bridge plate. While the bridge plate was off it gave me ample opportunity to look at the bracing and it is glued solid and tight. So I made a new bridge plate, glued it in, strung it up and guess what?

The distortion is still there

I just cannot help at this point but to think this is an act of God. After all this is wood, mother nature, a biologic system of imperfections and so on.

I will say that it's a bit 'better' but it's still there.

And I did manage to get the plate out almost intact and as far as I could tell there is nothing wrong with it. You know in thinking about it, the distortions are almost on the same side which corresponds to the book match. If the top had some failing on one side it would be replicated on the other. Same as the bracing, as was mentioned earlier, if they are cut successively off the same stock then that error would be replicated on either side.

My thinking now is that there is a weakness in the X-brace and the twisting motion of the bridge is exposing that weakness and the X at that point is twisting and pulling the top with it. If I carved these braces in cross section as a parabola then perhpas it would have kept more of it's strength. I carved them triangular.

Image (not the top on this guitar) to outline my thinking. Thanks for putting up with me as I try and figure this out

Do you flex the x-braces as you are carving them? It seems like if there was something weird going on with them you would notice it at that point.

New username, same Pat Mac

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Pat

I still question the thickness of the top. Those braces look plenty stiff you would only get a marginal difference going from the triangle to a curve top on the braces. By design under tension the bridge rotates putting tension on the back or the bridge. If the top is too thin you will see the distortion of the top just where you see.

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http://www.Harvestmoonguitars.com

Note: Mc said the pic right above is not the quitar in question so we must ignore the bracing, plate and plate. Mc is just trying to show the forces he is imagining.

Right, that is not the top in question just an image that was properly orientated to show my thinking.

I carve the braces after they are glued on so I don't flex them per se. I do look after them after they are prepped for gluing though by flexing them just to see if there is a split in them or that sort of thing.

And I use deflection to determine the top thickness not just a measurement. So some tops come out thin but are stiff, some come out thick and are less stiff and so on. This particular one was made stiffer then 'normal' though the top was a reasonably thickness. I'd have to look at my notes to remember. But again deflection is really what I go by. The X on this guitar was 1/4 X 5/8th.

So yeah... Back full circle. I'm thinking it's a twisted beam.

The bridge under tension is suppose to rotate a bit so the top will distort as well. My thought is that if a top is too thin the structural elements and the stiffness they provide will teligraph through. I am saying this because I just re-topped an instrument with the same issue.

You might check the rotation of the bridge under tension on both sides to see if it is twisting. If you have a smart phone an easy way to test the rotation is to use some putty to stick a smart phone on the bridge and use an angle\level app to see if one side is moving more than the other or if the bridge is over rotating. Trevor Gore suggests 2 degrees is good.

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http://www.Harvestmoonguitars.com

If the distorsion goes away when the string tension is removed you could glue a reinforcing patch in the location where it occurs and maybe save yourself a retop. Eliminating a cosmetic flaw with a little bit of inconspicuous wood would be something I would try first.