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Perfect Repair Gone Deadly Wrong
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=22941		 Page 1 of 1
Author:  vm3usic [ Thu Jul 02, 2009 10:28 am ]
Post subject:  Perfect Repair Gone Deadly Wrong
Hey,

So, I had an Epiphone acoustic guitar and I wanted to fix it. More of the story is offsite so I'm just going to link it rather than type it out all over again. There's an image of the end result. Why did the glue snap like that? Was my repair bad? The reason I'm guessing is because it got so hot where I live, the wood glue simply started to get sticky again and snapped under the pressure of the strings and the weakness of the glue. What do you think?

http://vmusics.blogspot.com/2009/03/headstock-repair-1-process-and-after.html

Image
Author:  douglas ingram [ Thu Jul 02, 2009 10:42 am ]
Post subject:  Re: Perfect Repair Gone Deadly Wrong
From what I can see:

There is not much surface area for the glue joint to work on. What you have there is essentially what is know as a scarf joint. For this to work well you need at least a 6:1 ratio of length to height, 8:1 is common, and 12:1 is really good. You have, maybe, a 2-3:1.

The glue that you are using should be OK, but it is a thin set glue, which means that the gluing surfaces have to match perfectly. If you can't be sure of that, then a thick film glue like epoxy would be the glue of choice.

This glue joint has its greatest stress on the back of the headstock, where the pull of the strings is trying to stretch the joint apart. A back strap applied over the joint will help significantly

This kind of break is notorious with Gibsons and, by extension, Epiphones. Keep on trying, you have nothing to lose and everything to gain! Keep trying, and good luck!
Author:  csullivan [ Thu Jul 02, 2009 11:22 am ]
Post subject:  Re: Perfect Repair Gone Deadly Wrong
Hi Robert,
Douglas is right about this being a common repair on Gibsons and Epiphones. It looks like you used Elmer's carpenter glue, an all-purpose white PVA glue. It would have been better to use Titebond (a yellow glue), but a good grade of epoxy would have been my first choice. The epoxy bonds the irregular surfaces together fairly well, although you will still be able to see the repair. You also said you waited a few hours before stringing it up. Even though it seemed to be bonded, a few hours probably isn't enough time for the glue to cure completely. Twenty-four hours would have been better. Over the years I have found that the best way to make this particular repair is to plane the two broken surfaces flat, cut a piece of mahogany (in this case) oversized in length and width to amply cover the area being repaired, but the thickness is the total amount of wood removed from the neck and headstock. Glue the sandwich of 3 pieces together. When the glue has cured you then reshape the area back to original. It then requires refinishing. I have made this repair so successfully that clients absolutely couldn't find the repair. This method also makes a repair that will stand the test of time. But even if you choose the epoxy route you will probably have a repair that, while not beautiful, will survive for quite awhile.
Craig
Author:  Barry Daniels [ Thu Jul 02, 2009 11:42 am ]
Post subject:  Re: Perfect Repair Gone Deadly Wrong
There were pieces missing on the front and back. You can't leave it like that and expect it to hold. You need a backstrap as previously mentioned, and a headstock veneer replacement.
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