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Thread: Acoustic Guitar Head Repair Advice

  1. #1

    Acoustic Guitar Head Repair Advice

    I have a Martin D-15 from when I was younger that I loaned to a friend and returned with a cracked head many years ago. It's sat in its case for all that intervening time but I thought I should go ahead and give it a repair and perhaps leave it up at the cabin so people can give it a play when the mood suits. It's worn from happy use and has character I like - it's time for it to be played again.

    I was hoping for some advice on proper repair. Obviously my thought was to fill a syringe with hide glue and inject it into the cracks, then use a wooden handscrew clamp to really get some force down to close the crack. Easy cleanup afterwards, etc. Should I just mix it normal or thin it more so it "seeps" into the cracks better. Should I add any urea to extend the working time so that I can let it flow into the cracks better before I clamp?

    I also have some System 3 epoxy with a medium hardener - about 30 minute working time. Since I'm using it for another project right now I was mildly considering it given how tenacious the hold is, but the cleanup on the mahogany seems like a no go - would hate to have to scrape it and work the finish again.

    I'll remove the tuners before I glue it. Given where the cracks are I was just going to ignore the truss rod, but do you think I should loosen it too?

    I've included pictures for reference. Any thoughts appreciated, just want to make sure I'm not missing something obvious that a luthier or someone more familiar with this work might see.

  2. #2
    Join Date
    Feb 2008
    E TN, near Knoxville
    I haven't done it with a guitar but I've fixed other wooden things by first breaking them apart completely at the crack then gluing. I found a guitar repair web site that seemed to say the same but I didn't read it all. When I did it I had to carefully remove splinters that kept the pieces from mating seamlessly.


  3. #3
    Join Date
    Sep 2013
    Wayland, MA
    Google "Frank Ford" and headstock repair. You will find a number of articles like this one where Frank shows how to make various crack repairs. Frank is the resident guru at Gryphon Strings in Palo Alto and the guy you want to take your $50K pre-war Martin to.

  4. #4
    Thanks John, I had briefly considered breaking it apart completely as well - it's just a hard pill to swallow. I think I'm going to go for the repair without breaking it apart first. And since it's hide glue if that doesn't hold perhaps revisit breaking it completely if the time comes.

    Great links Roger, very helpful. Looks like the trick is in the cauls. I can't tell if he's using plywood or several pieces of laminated fibreboard or something. I'd imagine the later since they have some flex. I also have some leather I might use to soften the cauls and then use the jorgensen clamps like he has since they exert quite a bit of pressure.

  5. #5
    Join Date
    Feb 2010
    Pueblo, CO
    Looks like cork on the cauls to me.

  6. #6
    IF and this is a big if, the crack closes cleanly when you squeeze it together, I would pull the tuners, inject some hot hide glue in there, use your compressor to blow the glue in further, inject a bit more glue and clamp it down with two pieces of wood with packing tape on the faces so they don't stick. Clamp it until you see the crack close and some glue squeezes out. Wipe off the squeeze out and let it sit in the clamps for 24 hours. Should be good to go. Let it sit for another 24-48, string it up and enjoy it.

  7. #7
    Thanks to all. I was able to make the repair late last week and let it sit over the weekend to fully cure. I had some fiberboard that I had used for cauls for an earlier project and just cut them down and faced them with some leather. Shop was cold so I used the heat gun to preheat the head and then hung the guitar from the rafters so the hide glue could migrate down the crack when applied with the syringe.

    I'd say for anyone doing a similar repair in the future it has to be hide glue for no other reason than the clean up. I just used a nylon cleaning brush and hot water and all the residue came off readily. I used a dental pick inside the tuner holes and it picked off easily as well. I can't image what a pain it would have been with any other adhesive.

    I briefly tried to apply some shellac to blend the crack but it turned out to not be that great of an idea - it drew attention to the crack as it was too glossy and I didn't want to mess with the general finish.

    Have had it tuned up for several days and no issues - plays great!

  8. #8
    Join Date
    Sep 2013
    Wayland, MA
    well done, congrats on your success!

  9. #9
    You could get some deft or copal and fill the crack, then level. But you'd definitely run into some finish retouch as well. Kudos for using hide glue and doing it right! Should last forever, unless subjected to high heat/humidity.

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