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I would not write it off completely Filippo but it does not look like an amine problem to me. The affect is usually a softening of the finish and raising of the glue line yet the images clearly show cracking and fracturing that seems more in line with excessive wood movement. The coco you have used for the cap is beautiful but does look like it could be quite reactive and it is my guess that variation of movement has been the culprit here as you have suggested.

EDIT: In the second image, it is hard to see clearly but it looks like the glue line in the centre of the bookmatched cap has opened or risen just a little, can you 'feel' that line when you gently rub your finger tip over it?

Cheers

Kim

Looks to me like the grain of the heel cap is at 90 degrees to the neck..? If it is, no doubt that is the problem....!!
Tom

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I've always thought fully cured epoxy that was properly mixed is inert.

I vote for wood movement.

Kevin Looker

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Looks like movement to me also.That can happen with burl because of the wild endgrain that soaks up any liquid and decides to move. At least it's nitro and can be drop filled and fixed.I would seal that cap real well first though.

I would wait a little while and let what ever is happening in the wood to settle down then refinish that area. You have a lot of different woods all together in that area, it sure looks good, I hope you can get it under control.

Pictures could be larger, the details are hard to see.

Fred

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Guess a movement issue also. I see this all the time with numerous wood laminations and grain direction competing for the same space. Happens in every facet of woodworking. Sometimes you are lucky and sometimes your not. Hard to say which wood here was the actual culprit. I'd let it go for a bit longer before doing a fix...just to make sure its done with most of the movement. It'll never be done moving....It's just at what rate and what extent.

Kent

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Boy, that really sucks, Filippo.
Wood..........
Just when you thought you were done.

Those are cracks formed as the result of localized stress...I've seen hundreds of these. Note the finish is lifting primarily off of the cap side of the fissure and less so on the neck side. This indicates not only a tiny relative movement between these parts but also the direction of movement. The finish stays on the neck because of the relative direction. On the neck side of the fissure, the finish is being pulled indirectly back toward the neck and on the cap it is being pulled indirectly away from the cap.

Local stress.... The cracks may indicate too much movement of the neck right at the heel....but not necessarily.

Was the cap glued to the neck prior to joining it to the body? If so....the glue line of the cap to the neck and the glue line of the cap to the body are two seperate gluing operations, which allows for the possibility of having made some kind of gluing error when the cap was glued to the neck.

Here's a theory. I'm guessing you glued the cap to the neck prior to setting the neck into the body. The glue joint of the neck set has integrity. The glue joint of the cap is compromised. When the strings have tension the neck bends forward and applies the kind of stress indicated. PROOF of this theory would be if someone noticed that the cracks began at the tip of the cap and then propagated toward the body over time. I'd ask the customer if he noticed this. That would be a 100% indication that the neck has localized stress at the heel....not necessarily a disaster....but not happy either. If this is the case then it begs the point that the cap area has a lot of stress there and in order for this geometry to work the bond of the cap to the neck must be very solid.

An interesting observation might be to let it go for a while and see if the neck joint holds up over time by itself as the stress becomes more concentrated on the neck set as the bond between the cap and neck continues to fail. If the neck set holds up then the answer for this might be to make the heel a little deeper next time and make that cap much thinner. This would relieve lots of stress between the neck and cap for the given movement in that area.

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StuMusic

I thought of that too, Zlurgh,
you might be right, but, if the neck was flexing,
wouldn't the separation be at the smaller glue joint where the cap meets the body?
I think it's wood shrinkage.

I vote for wood movement here as well.
However, cured epoxy often has a film of 'amine blush' on the surface after curing. (Thus the comments by Filippo and Kim.)
This has to be removed or you will have finish (and subsequent epoxy lamination, if applicable) problems. This is more often a problem with epoxy coatings, epoxy-fiber laminations and the like.

John

Yes...possibly....if the cap was glued on after the neck was set. In that case both the neck/cap and the cap/body joints would have been glued at the same time....and be the same glue. In that case it would have probably cracked only on the cap/body edge....and not where it actually did crack.

But...if the cap was glued onto the neck prior to the neck set, then there are two distinctly seperate gluing operations that affected the cap...and potentially, two different glues. If the cap/body glue joint had integrity as the cap/neck joint crack propogated then, if the weakened neck joint is not sufficient to hold the load, the likely scenario from this point on is that the neck joint itself will fail while the cap stays happily glued to the body by that little edge....content to exist in a stress free environment.

This is only a theory. Phillipo will have to monitor this to see what happens. I'd sure like to magnify that cap/body joint to look for microcracks. If there are microcracks there, the direction of force applied to cause them would orient them perpendicular to the load...causing a visual stress pattern. Seeing a pattern would definitely help to tell whether it was neck bending stress or shrinkage that caused the problem.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I have highlighted what I think could be a couple of indicators to what may be going on. Arrow "A" points to the bookmatch joint of the cap and it looks like it may have opened just a tad as I think I can see just a faint tell tail line. This could be due to the cap itself expanding under the finish causing delamination of the finish from the adhesive below. Arrow "B" shows the main crack in the finish is at the 'longest' point of the cap and is in a horizontal plain to the cap. This seems to indicate that the cap itself has expanded 'vertically' and again has caused delamination of the finish from the adhesive line below. The fact that the largest cracks are at the furthermost point away from the body seems to suggest that the neck to body joint is least affected.



Cheers

Kim