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| What glue for broken peghead http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50297 |
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| Author: | Bryan Bear [ Mon Feb 12, 2018 12:45 pm ] |
| Post subject: | What glue for broken peghead |
I am working on a guitar that has a laminated neck and a scarf joint. The laminations are maple/jatoba/maple/jatoba/maple where the 3 center laminations are just over 1/2” wide. The blank was laminated then the scarf was cut and glued. I glued the front veneer onto the peghead then made a stupid mistake when gluing the back veneer on. I like to do the curved volute on the back of the peghead requiring the back veneer to be bent to match. In order to ensure the veneer (about 1.5 mm thick bubinga) gets clamped well, I use a caul that is shaped closely to the curve on the back of the peghead but also sandwich some firm foam between the caul and the peghead then clamp it all really hard. The heavy clamping pressure compresses the foam and evens out any gaps the caul may have had. Well. . . this time I screwed up. Without thinking, I used two cauls for the front of the peg head instead of one. That meant that the force compressing the foam wanted to bend the peghead at the space between the face cauls. Snap! I now have a broken peghead with the back veneer in place and the face veneer broken at the inlay lines. I can tell from looking at the sides that one side was wood failure but the other looks like the scarf joint failed (I’m not sure how much is wood failure and how much is glue). I don’t know if the 3 center lams broke or the joint failed. I can easily push the parts together and close the cracks because the back veneer is holding strong. If it were all wood failure, I would work some HHG in there, clamp and never give it a second thought. But since I know there will be some part of the joint that is old titebond I don’t know what to do: 1) Proceed with HHG because it will stick well enough to TB? 2) Use epoxy because it will stick to TB? 3) Remove the veneers somehow, get to bare wood, reglue and make new veneers and inlay 4) Make a new neck |
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| Author: | StevenWheeler [ Mon Feb 12, 2018 1:11 pm ] |
| Post subject: | Re: What glue for broken peghead |
Hey Brian, Maple, Jatoba and Bubinga are reasonably priced and your free time of late has been sparse. Make a new neck. You would have better luck gluing this one with titebond. It's certainly not an optimal joint but TB will stick to old TB better than anything else will and the fresh glue joint and veneers should make it strong enough. Steve |
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| Author: | Bryan Bear [ Mon Feb 12, 2018 1:25 pm ] |
| Post subject: | Re: What glue for broken peghead |
I hear what you are saying. The new neck option is not a mater of price but time and procurement. I'm not looking forward to thicknessing all those laminates and getting back to where I was (almost completed neck) and I don't have anymore of the maple I used (that I know is long dry). If I do make a new neck I will probably use cherry and rework the aesthetic scheme a bit. I suppose before I did that, I could reglue the joint and do some serious stress tests since that wouldn't take long and there is no downside. I'm surprised to hear that TB sticks to itself better than other glues. That was not my understanding. Aint learnin' fun? |
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| Author: | StevenWheeler [ Mon Feb 12, 2018 2:26 pm ] |
| Post subject: | Re: What glue for broken peghead |
Well, perhaps I misworded that a bit. It would be my first chioce in a situation like yours. It's been a few years since I've seen your work, but I don't imagine you've gotten sloppy with your joinery. If some of your laminations broke and on one the joint let loose, I would lean towards a glue starved joint in that area. I have found that TB will reglue this joint better than other choices. A similar situation where others have reported success re gluing with TB is on soundboard center seam splits brought on by lack of humidity. Again, on this situation I'm leaning toward a glue starved joint. A poorly made joint with a thick pva or ar glue build up is not going back together with the addition of more of the same. |
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| Author: | Bryan Bear [ Mon Feb 12, 2018 2:39 pm ] |
| Post subject: | Re: What glue for broken peghead |
You bring up a good point about the quality of the joint. I was surprised and saddened when I saw partial joint failure. I can say with confidences that there was not a thick glue line. I've never had an issue like this so I was worried about what I did wrong but encouraged that at least half of the joint was wood failure. You could be right about the joint being starved; I hadn't thought abut that. I know it was clamped well and the joint was only visible by the change in grain direction. Considering that one of the faces in a scarf joint shows a fair degree of endgrain it very well could have been starved. I think I'll try to open it enough to get a peek inside there and see if I can see any glue or shiny surfaces. |
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| Author: | jfmckenna [ Mon Feb 12, 2018 4:02 pm ] |
| Post subject: | Re: What glue for broken peghead |
I would need to see a pic of what you are talking about to be clear. But if I do understand it correctly you are only worried about the lamination that are Titebonded together but not the crack? I have tested Titebond to Titebond joints and have been quite surprised with the strength of it. It's not ideal by any means but it can be strong especially if it's mixed in with wood to wood contact. I would just try gluing it before making a new one. If it comes out good then you win, if not then well, now you know what you must do. |
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| Author: | Bryan Bear [ Mon Feb 12, 2018 4:27 pm ] |
| Post subject: | Re: What glue for broken peghead |
jfmckenna wrote: I would need to see a pic of what you are talking about to be clear. But if I do understand it correctly you are only worried about the lamination that are Titebonded together but not the crack? I have tested Titebond to Titebond joints and have been quite surprised with the strength of it. It's not ideal by any means but it can be strong especially if it's mixed in with wood to wood contact. I would just try gluing it before making a new one. If it comes out good then you win, if not then well, now you know what you must do. No, I don't think there is any delamination of the joints that run the length of the neck. I can see that the peghead broke along the grain on one side and the other side looks to be, at least partially, a failure of the scarf joint glue line. The three center laminations are either broken along he grain or failed at the scarf joint but I can't see in there. |
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