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Thread: Cracked neck block

  1. #1
    Registered User Doug Edwards's Avatar
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    Default Cracked neck block

    Ouch, the neck joint failed and the block is cracked. Any definitive way to correct this along with gluing. Also, hide glue, Titebond, or System Three epoxy? Thanks

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  2. #2
    Registered User sunburst's Avatar
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    Default Re: Cracked neck block

    You can glue it, but then you essentially end up with a butt joint for the neck because the side grain joint that was originally there is no longer of any particular use. The neck tenon would still be glued to the side of the tenon, but one side of the tenon would be relying on the butt joint that would be the repaired crack.
    In the past I have fit a large block of wood into a broken head block with a dovetail joint and then reset the neck into the repaired block, but that was a mandolin worth many more thousands of dollars than I suspect this one is worth. I'll see if I can find the old thread on that one and post a link...

    Epoxy might be the answer in this case.

    Edit: No luck finding the thread on the head block rebuild.

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  4. #3
    Registered User Doug Edwards's Avatar
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    Default Re: Cracked neck block

    I seem to remember the thread to which you refer. Also it may of been on your new website at the time. I see what I can come up with. Just about have the old glue removed. Slow go as I’m basically one handed. I’m two weeks after my total shoulder replacement surgery. And yes it’s not worth that much, but priceless to me. It was my first build that I dedicated to my mother. Thank you John, you’re an ever present help. Appreciate you

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  5. #4
    Registered User sunburst's Avatar
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    Default Re: Cracked neck block

    Oh, I see: Your mandolin, your time, valuable to the owner. Spend as much time and effort as you wish, economics are out the window!

    Be good to that shoulder, follow the PT advice and heal at your own pace.

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  7. #5

    Default Re: Cracked neck block

    Could you fill the dovetail either side to make a straight mortice, then cut the dovetail on the neck to a tenon, and then make it a bolt-on? I think this is what John was suggesting. As a mere amateur builder I'd certainly find it easier to fit pieces either side and then pare back to shape the mortice, rather than trying to shape a full insert and then cut the mortice out of that.

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  9. #6
    Registered User Tom Haywood's Avatar
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    Default Re: Cracked neck block

    Is that block mahogany? If I see the photo correctly, that area is perhaps the weakest point in the wood, and mahogany seems to split easily sometimes. I recall Sunburst's post about inserting a newly cut mortise. My thought is to glue on a thick shim on that side, maybe a piece of maple or ebony, using original TB. The downsides would be trying to pull that section of block back together and hold it while gluing the overlay; and the neck tenon would have to be cut on that side making it uneven and possibly weaker. Good luck!
    Tom

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  11. #7
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    Default Re: Cracked neck block

    Another approach would. be to drill a hole through the top and angle through the crack. Then epoxy in an 1/8" CF dowel. If the crack will close, you should HHG it first and clamp together with large rubber bands.
    I've fixed a few that way and they hold up.

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  13. #8
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    Default Re: Cracked neck block

    I've stared at the picture a dozen times. Definitive way?? Open the back and replace the block. Difficult and invasive.

    I don't think there is room to cut the block out of there in pieces and install a new block without opening the back.
    But cutting all or part of the block out first might make it easier to open the instrument. If you get really lucky, it might then be possible to install a new block without removing the back completely.
    Still very difficult.

    Alternative? Regularize the crack, insert a splint, and cross your fingers. Difficult. Less invasive. Reliability not guaranteed.

    I don't think filling the open crack with epoxy will be reliable over the long term. The crack must be closed, or splinted with wood.

    I think I would insert a splint first and hope for the best. A thin reinforcement over the face of the repaired crack wouldn't hurt if there is room. If that doesn't hold, open her up and replace the block.

    Whatever you choose, good luck.

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  15. #9
    Registered User Doug Edwards's Avatar
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    Default Re: Cracked neck block

    Quote Originally Posted by sliebers View Post
    Another approach would. be to drill a hole through the top and angle through the crack. Then epoxy in an 1/8" CF dowel. If the crack will close, you should HHG it first and clamp together with large rubber bands.
    I've fixed a few that way and they hold up.
    Pretty much how I thought using counter sink screws and dowels. The neck would cover the holes. Tempted to remove the back. Maybe should it fail again.

  16. #10
    Registered User sunburst's Avatar
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    Default Re: Cracked neck block

    Screws might improve strength if there is plenty of sound wood to hold them, but dowels will not add strength.
    A couple of well placed and well installed screws with counter sunk heads covered by the neck heel would probably give you a playable mandolin.
    A new head block would, of course, be the best repair but it is a complicated repair and not for the faint of heart and would be made significantly more difficult working with one hand!

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  18. #11
    Registered User Doug Edwards's Avatar
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    Default Re: Cracked neck block

    Thanks John. Thanks I am working mostly one handed. Fortunately the surgery was my left shoulder and not my right. I start therapy Monday.
    I was able to machine a couple screw heads done below 13/16 and counter sink them out of the way. They pull the spilt block together nicely. Ill most likely glue some veneer in place to tighten the joints.

  19. #12
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    Default Re: Cracked neck block

    If the screws pulled it together, you might try backing them off and see if you can get some glue into the crack, then tighten them back up.

    But I had forgotten about that shoulder. It might be better to wait until after your PT appointment before you do anything else. You don't want to mess up your doctor's work.

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