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I'm struggling to figure this out but I need to make this a learning experience and move on. Here are the details:

1) Top is Sitka
2) X-Brace at 96deg and 1/4in bracing Sitka
3) Bridge patch: Flat Sawn Osage Orange laminated to QS Spruce (grain direction of spruce same as top)
4) Bridge is BRW and the x-Brace extend through the lower corner of bridge wings
5) straight bracing, not scalloped

None the less the top is extremely distorted at the bridge corners. I use deflection testing for the top and this top I have made stiffer then most. In fact the last guitar I built deflected twice as much and has no problems and is of the same design.

I double and triple checked and the bracing is definitely not loose.

The only thing I can think of is that the X is twisting. The distortion is right on top of the X-Bracing.

Here is a pic of the bass side:



Here is the treble side, It's harder to see here because it's not as bad:



Here is a shot of the bracing:



This is extremely disappointing and I'm struggling to figure out what the problem here is, any input would be greatly appreciated. I have no other choice but to retop this guitar. But I want to learn from this and never let it happen again.

Regards.

Wish I had an answer for you.

Why do you feel it needs to be retopped?

Was the top plate thickness in your normal range? The braces can make the top stiff as read by a deflection test, while a thin top can telegraph the braces and\or stress points around the bridge. I had to retop my 8 string nylon crossover because the top was too thin. It did sound nice though, I did not want it going to a client that way.

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http://www.Harvestmoonguitars.com

Flat bridge glued to radiused soundboard with brute force clamping pressure?

That's exactly the position I am in. This is not deliverable. I don't even really measure thickness. Well, I do and I enter it in my book, but none the less I hold deflection as the more valuable measurement when designing the top. And that's why it's confusing because this top was stiffer then what I usually go for because I was going for a more treble tone.

Ed, The pics don't do it justice. If you run your finger over this you can really feel it. I usually go for a bit of bridge rotation and top belly but in this case there is something else going on.

Dennis, I forgot to mention, both the bridge and the bridge plate were arched to accept the top. The bridge and plate were glued down with an arched caul as well.

Yes, I could see that being a problem if it's for a client. Just out of curiosity, did you measure bridge rotation? Is a laminated bridge plate your usual practice?

No it's not a usual practice but I have done it before including the last one which was essentially the same as this one only the top was twice less stiff... Hence my confusion.

Hmm, this really is a stumper. How long has it been strung up? How much distortion remains when the strings are loosened?

That's a real stumper. Can you please let us know what you discover?

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Thank You and Best To All

Good question. I strung it up for a week now and it slowly progressed to this point and stopped. The distortion almost goes away when the strings are off but it's still there.

Some reason I can't see the pics?

Me either.

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Steve Smith
"Music is what feelings sound like"

Me either

I also can not see the pictures!

I can't see them either, but they were visible this morning.

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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

Since I can't see the pics either, I'm going to take a complete stab in the dark.
Is your bridge patch in the correct position? With a hardwood patch I shoot for 1/8" in front and behind the bridge, when doing a softwood laminate I add another 1/8" in either direction.

Steve

I hate Google Photo's!

I re-posted the images. Hopefully you can see now.

I can see the first two. The bracing shot is still missing on my feed anyway.

Yep, the two outside photos are showing again now, but not the bracing.

I saw the bracing picture earlier, and the bridge patch extends plenty far behind the bridge. The distortion is happening right on the bridge patch, which is part of why it's so puzzling. It shouldn't be possible for such a thick sandwich of material to deflect so much.

jfmckenna, check again that the lower corners of the bridge patch are still glued down. See if you can stick one hand inside the box, hook your finger around to get your nail at the potential gap, and then push down on the soundboard from outside to try and flex it open.

Might there be a void in the bridge patch lamination? Layers separating?

That is strange. The deflection appears to be right over, or at least close to the x, but it doesn't seem to be influenced by the x. Strange indeed.

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Joe Beaver
Maker of Sawdust

So some thoughts and I'm just going to throw these out for discussion sake.

That kind of distorion almost always happens when a brace isn't glued well enough. I've fixed it on numerous guitars. I'm not trying to sound accusatory but are you 150% certain that the braces are glued well enough?

On the bridge. Possible that your glue joint is stronger on the wings than the middle?

On the bridge plate. What's the grain orientation of the osage piece?

Do you do perimeter sanding? The top might be thin around the edge. If the top regains it's shape when you loosen the strings you could add a tall finger brace (a.k.a. side tone bar) where the deformation is occurring and see if that helps.

Can't see any but 3 photos JF...

I tried posting the pic again.

I know what you are thinking because I had the same thoughts but the Bridge patch is absolutely 100% not coming apart. The braces are not loose either.

I do normally thin the edges but not on this one

The osage is flat sawn, spruce is QS along the lines of the top. Nice stiff and light plate it was.

I'm thinking that the X is actually twisting and that a 1/4in X-Brace at 96deg angle is too much. Thoughts?