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Thread: Bowlback sunken top

  1. #1

    Default Bowlback sunken top

    I have been given a bowl back which I hope to fix up and then give away to a player. It is by Gennaro Rubio, dated 1897, who I gather made reasonable quality mandolins in Naples. This is definitely an entry-level model, but rings out nicely when tapped with a knuckle.

    The only real issue I can find is that the braces (the brace aft of the sound hole and the brace at the cant) have come unglued at their left-hand ends (as viewed in the pictures). Because it was left strung up, the top has sunk.

    Easy enough, as hide glue appears to have been used and the braces are firmly glued for over half their length.

    Except ...

    The top has taken a set into the dip, and I can't force the loose ends of the braces to the soundboard using finger and thumb. I could put a clamp on each of them of course, but I foresee a loud cracking noise as I tighten the clamps.

    So ...

    Am I being a wimp, and clamping alone will work?

    If not, is there a way to try to remove the set? My guess would be applying heat, as if for bending, and then using clamps and cauls. If that might work, the pick guard will need to come off, and I think its very thin celluloid, so any tips for that?

    The fretboard lines up with the top nicely, so it looks as if the action would be fine if I could achieve this. Then I'd just need to fettle the tuners and do a general cleanup to make this back into a player.
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  2. #2
    Mando-Accumulator Jim Garber's Avatar
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    Default Re: Bowlback sunken top

    I am not expert on fixing this but one possibility would be to humidify the whole mandolin for some time and then gently regluing/clamping the braces. Others more knowledgeable might have a better method.
    Jim

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  3. #3
    Mandolin & Mandola maker
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    Default Re: Bowlback sunken top

    Is difficult without actually seeing the mandolin, but I would probably remove the top and go from there. Then you have proper access and can decide what really needs to be done. I think forcing it together with clamps is not a good strategy for the longer term. It is not too difficult to remove the tops of these old mandolins, they are glued with hide glue and old hide glue is often brittle and easy to get apart. I have been in a similar situation where you don't really want to take the top off, but it is the only way to fix it properly. It probably means you need to remove the fingerboard first. That can sometimes be a good move because then you can make sure the neck is straight, and sometimes you might need to replace the fingerboard. These old bowlback mandolins can end up taking a large amount of time to get them playable again, and it is a matter of how much you want to invest in it.
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  4. #4
    Registered User Tavy's Avatar
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    Default Re: Bowlback sunken top

    If you can get hide glue and/or steam into the sections that are loose then it should clamp up without too many cracking noises Different story when it's dry, and there's probably old glue and dirt in the join keeping things from coming back together.

    But.... getting glue into the brace under the bridge is pretty darn hard, so on that one I would go straight for top removal and then glue everything back together properly. You remove the 10th fret, cut through the fretboard and top at that point, then use a knife to prize the top off at one point (which will do a little damage), and then work your way around (which shouldn't do any more). If there's a part of the top that's already loose, then your away. Only difficulty is separating the top from the neck block - a bit of careful brute force usually does the job. The whole process will scare you witless first time you do it, then afterwards you'll wonder what all the fuss was about

    There is another option for getting glue into hard to reach braces which I don't like so much as it involves drilling a small hole either in the top, or through the binding, and then using a syringe to inject fresh hide glue. I regard that one as a last resort for use where the binding would self-destruct if you tried to remove the top.

    With regard to the pick guard - they were put on with hide glue too, and usually pretty much fall off once you lever up one corner. Occasionally you get one that won't budge, but you'll know pretty much right away which you have.

  5. #5
    Registered User John Kelly's Avatar
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    Default Re: Bowlback sunken top

    Re being scared witless, Tavy, some while back I was repairing an old fiddle for a friend. The neck needed to be reset and my first question was "Is this a valuable instrument? If so I will not even start on it". Assured it was not and that she just wanted it to be made playable again, I decided to have a go. A previous "repairer" had removed the fingerboard and added in a pine layer to raise the board, but he had not tapered this, so all it did was to have the fingerboard at a still unplayable angle but just a bit higher! I decided to loosen the neck joint and this worked very easily, the hide glue yielding to gentle warming and careful use of syringe with hot water.
    Then came the dilemma: although the joint was loose the neck would not detach; something was still holding it in place. I decided against brute force and thought I'd take the soundboard off. This is where your story rung so true with me. Warming the palette knives and working them gently round the seam did a fine job and even the neckblock and tailblock were successfully dealt with much in the way you described. When I got the top off, I could see instantly why the neck would not come loose - some earlier repairer, maybe even the same one who had added the pine riser, had inserted a cross-headed bolt through the neckblock and into the neck from the inside. I imagined the result if I had gone ahead and tried to get the neck off by extra force! A great learning experience and the rejuvenated fiddle is still being played by a happy owner.
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  7. #6

    Default Re: Bowlback sunken top

    The braces are reachable - my fingers are long enough to feel where the separation is, so I reckon I could get hide glue into the joints without too much difficulty. And nothing else is remotely loose, so I think I'll try a non-invasive repair first.

    Thanks Tavy for the advice on the pickguard.

    Where I think I'll start is by trying to flatten out the dip as much as possible - I'll apply localised heat and moisture and light clamping in stages to see if I can remove some of the deformation. If I can get close, then glue and clamps should do the rest. If not, top removal.

    Thinks ... clean out old hide glue first in case the steam partially reactivates it!

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