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Mysterious Glue Failure


bkwood
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Over a year ago I loaned a few of my fiddles, one at a time, to someone interested in buying one. He brought one back saying the fingerboard had fallen off. That seemed weird but I told him I’d repair it and get it back to him. He was actually more interested in another so the fiddle sat around for a long time before I got to it. When I did I took the opportunity to refinish it before returning the fingerboard. A couple weeks ago it was finally done and I loaned it to a friend of mine. He brought it back tonight to play some tunes with me, and as he opened the case and took it out the fingerboard slid free again. The first time it was an anomaly. I reglued it well, after cleaning both faces. There seemed to be no glue showing on either piece the first time. I’ll see what the latest looks like tomorrow. But could their be a contamination issue from the fingerboard blank I used? Has this happened to anyone? For an area with that much contact to fail twice without even stress on the joint doesn’t make sense.

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Clamping too tightly Might starve the joint. Not warming the fingerboard and neck could lead to failure.  If it isn't ebony it might be a wood that needs to be cleaned with mineral spirits or etoh. The ebony alternative boards, corene and such, don't work well with hide glue.

It could be many things. What about the glue? I was sold some marginal quality glue some years ago that resulted in a few reglued things...

 

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Sounds like you are trying to glue with a little bit of glue and or the joint is too dry. Or a thousand other possibilities, I'll focus on this for now,,,,,

Personally, I will, glop some glue on the neck, smear the board around, pull it off and look to see what the parting surfaces looks like.

Then I throw on some water and smear the board around again.

If it slides around and won't stick, wood to wood, but slips all over. I pull it apart and slop some more water on.

When it finally will grip the wood, I pull it apart and feel the glue, will it tack, how strong is it at this point, how slippery is it?

If I like it and it passes muster,,, I put it on and clamp, if I'm not happy I add water or more glue till I am.

I want it to have little beads of liquid around the edges of the board, if all is right it will hold forever,,, and it will snap right back off cleanly when it is time.

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6 hours ago, bkwood said:

 But could their be a contamination issue from the fingerboard blank I used? Has this happened to anyone? For an area with that much contact to fail twice without even stress on the joint doesn’t make sense.

Assuming that your fingerboard gluing regimen is sound, my next step (while the fingerboard is still off) would be to glue a small block of wood to the gluing surface of the fingerboard, and another to neck, and try to break them loose to get a better idea of where the bond is failing.

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3 hours ago, David Burgess said:

Assuming that your fingerboard gluing regimen is sound, my next step (while the fingerboard is still off) would be to glue a small block of wood to the gluing surface of the fingerboard, and another to neck, and try to break them loose to get a better idea of where the bond is failing.

Good idea.

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I took off the strings to see, and it's not what I had convinced myself it would be. I was pretty sure I either wouldn't see any glue or else I'd see the problem would be the ebony hadn't bonded. Actually, there is a clear glaze of glue on all the ebony surface but no evidence of glue on the maple. I've made a dozen fiddles out of the same tree, so I don't know what's going on. I suspect that in some unknown way I contaminated the maple surface with wax or silicone myself before the original glue up, and that I didn't clean up what I didn't see the second time. I don't understand how, but What else could it be?

Paint thinner, naptha? Suggestions for cleaning the surface?

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3 hours ago, nathan slobodkin said:

As David says If your glueing regimen is correct this is indeed pretty mysterious and his experiment would be interesting. Are you a professional maker? Gluing large joints like this can be tricky and it is most important that the surfaces match up perfectly requiring almost no pressure.

Oh, I forgot to consider that it might not fit! Hide glue is a crummy gap filler...

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8 minutes ago, bkwood said:

I took off the strings to see, and it's not what I had convinced myself it would be. I was pretty sure I either wouldn't see any glue or else I'd see the problem would be the ebony hadn't bonded. Actually, there is a clear glaze of glue on all the ebony surface but no evidence of glue on the maple.

 

Good detective work. spacer.png

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25 minutes ago, duane88 said:

Oh, I forgot to consider that it might not fit! Hide glue is a crummy gap filler...

I agree with that. The surfaces mate perfectly. Looking at the maple carefully it seems perfectly clean. One thing I did not do is apply glue to both surfaces, only the ebony, and maybe the room was cool enough that the maple was too cool. I usually use a heat gun to warm both surfaces, and my shop is usually warm. And I don't tend to contaminate glue surfaces with other materials. Like I say, it's mysterious. But I'm going to clean both surfaces and reglue them with all that in mind.

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30 minutes ago, bkwood said:

I agree with that. The surfaces mate perfectly. Looking at the maple carefully it seems perfectly clean. One thing I did not do is apply glue to both surfaces, only the ebony, and maybe the room was cool enough that the maple was too cool. I usually use a heat gun to warm both surfaces, and my shop is usually warm. And I don't tend to contaminate glue surfaces with other materials. Like I say, it's mysterious. But I'm going to clean both surfaces and reglue them with all that in mind.

You have to apply glue to both surfaces, that's your problem right there.

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1 hour ago, bkwood said:

I took off the strings to see, and it's not what I had convinced myself it would be. I was pretty sure I either wouldn't see any glue or else I'd see the problem would be the ebony hadn't bonded. Actually, there is a clear glaze of glue on all the ebony surface but no evidence of glue on the maple.

From this description, it sounds like the glue had started to gel before you got everything together.

To glue ebony well, you need a sound method, and to assemble things quickly.

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17 minutes ago, Strad O Various Jr. said:

You have to apply glue to both surfaces, that's your problem right there.

I do not apply glue on both surfaces, but only on the side of the neck and I have never had a loose fingerboard, so I think this may not be the problem. It could be a problem of too thin glue and excessive absorption (complete?) in the neck. I would try applying glue on the neck and letting it dry to see if it disappears or doesn't form an even layer. This will also give information on any contamination of the surface of the neck, and act as an impregnating agent to avoid absorption in the final gluing of the fingerboard. After re-flattening the neck surface, of course.

Without excluding all the other possible causes mentioned above and the possibility of concomitant causes added together, in the worst case scenario.;)

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50 minutes ago, Strad O Various Jr. said:

You have to apply glue to both surfaces, that's your problem right there.

I was taught: plane very slight hollow across the width of the board, perfectly flat otherwise, neck surface perfectly flat, heat gluing surface of board on hot plate, apply not-too-thick glue generously to fingerboard surface only, slide quickly into exact position with location guides, clamp. Never had a joint fail. It's a large gluing surface: most likely shortcoming is a glue bond that's too strong rather than too weak. Don't want to have to use a wrecking bar if it ever needs to come off...:)

 

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23 minutes ago, Rue said:

...have you seen videos of a string breaking during a concert, or a bow exploding? :)

Think how entertaining it would be to see a fingerboard fall off! :D

...

...

:ph34r:

I was once playing in an ensemble when the tail gut failed on one of the violas.  That was really dramatic.

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