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Thread: 1914 gibson H1 mandola sagging top, and bowed neck

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    Default 1914 gibson H1 mandola sagging top, and bowed neck

    I have this one on my bench for a repair estimate. Attached are photos, but the quality is poor, as the sag is difficult to catch, in a photo(but easy to see with the naked eye). I've been doing some research, and have seen Frank Ford's admirable and instructive photo essays at Frets.com. To properly correct this(and give the back has already been off, and poorly reglued), I believe the back should come off, the top curve corrected, and a small brace added under the bridge area. I suspect it would benefit(in several ways) from a adjustable style bridge, ala Cumberland Acoustics, partly because those are longer than the original, thus spreading the load. The sag is on the bass side at the bridge end.
    The neck has excessive upbow. Here, I'm reluctant to simply plane the board straight, because it will remove a relatively noticeable amount of wood & binding. I believe the best fix would be to remove the fingerboard, straighten the neck shaft(and maybe add CF reinforcement), then replace the board and refret(and replace the mostly missing binding).
    Whether the owner will want to pay for all that work, is a separate issue...Click image for larger version. 

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    Can anyone with direct experience comment, or make suggestions?

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    Registered User sunburst's Avatar
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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Sounds like a good plan to me.
    Removing the back makes top work easier because of improved access, and in this case it allows improvement of the back-to-rim glue joint.
    I think adding CF to the neck would be a good fix also.
    As you say, the owner will have to decide about paying for that amount of work, but it should be a good instrument once repaired.

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Before you settle on removing the back, loosen the strings all the way and inspect the top brace. Sometimes, when the brace is loose on one side and you push it into position, most of the top distortion will go away. If it doesn't, the instrument will probably have to be opened. If you remove the back, be prepared to encounter one or two short nails between the blocks and the inside of the top. The final decision about the best way to support the top should be made after the back is off. One alternative is to X brace the top.

    Removing the fingerboard, straightening the neck carefully with heat and clamping, replacing the board with hide glue and possibly a few thousandths of back bow, and a good tight fret job may be sufficient if the neck is stiff and the board is in good shape. If not, either a reinforcement and/or a slightly thicker fingerboard would be a good idea. If you reinforce with CF, set the rod slightly below the surface of the neck and cover it with a thin strip of maple. CF is quite difficult to sand, scrape, or file level to a neck surface. If you cover it with wood, it will be much easier to level the neck surface.

    Whether or not to change the bridge will depend largely on how stiff the top is after repairs have been executed. An alternative to an adjustable bridge is to cut a new bridge in the original but with a longer foot. If you look very carefully at the original bridge, you will see that it was actually made in two pieces: a base section and a compensated upper section. These are fairly easy to make-- rough out the sections slightly over-size, laminate them together, and cut to final shape after the glue is dry.

    The instrument can definitely be saved, but the owner will be looking at a large repair bill. I would either estimate on the high side, or give a minimum - maximum range. You really won't know the best way to execute all of the repairs until the instrument is on the bench.

    When the repairs are complete, the owner will have to be cautioned to string the mandola lightly. I recommend 12 -20 -32 - 48 or 50 for an old Gibson mandola.

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    Registered User j. condino's Avatar
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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Time for the once a century rebuild.

    -Back removal is fine; the no back binding on these makes it a straightforward task. Be aware that you may have to make a compressing jig to get everything aligned once the tension is released- see attached image.

    -I'd make a cast plaster mould of the top, then manually scrape it to correct for the variations back to what your ideal arch shape would be. Then the top is placed face down in the mould and gently heated with a combination of sandbag and heat (microwave the sandbag or gently warm it on the stove) to bring the original shape back. I do the same thing for ancient old double basses where the top collapse depth can be measured in multiple inches. You can also use a custom sized heat blanket very effectively, but be careful about not overheating it as the varnish will melt.

    -I like the idea of changing from a single transverse brace to a small X brace. It will be structurally stronger and the voice will have more harmonic complexity. I've done it a few times on old A models and everyone agreed it was a positive outcome. I've also done it on my new building test rig many times and you can tell an obvious difference.

    -Steam the neck and reset the heel angle rather than a bunch of add on compromises like planning the fingerboard down to nothing to correct the bridge height. It is a simple task once you have the back off, and if done correct, you won't need to make any fingerboard modifications.

    -Please perform all work with period correct materials- i.e. hot hide glue, et cetera.

    - An adjustable bridge will be useful for seasonal & setup adjustments, but it may sound slightly different than a solid contact fixed bridge.

    -If the work is done correctly, the finished instrument should be rock solid & there is no reason that you have to be delicate with string choices.

    -If the owner is unwilling (cheap, stingy, bottom feeder...), hand it back as is and move on. Don't compromise yourself or the instrument & make sure you get paid a proper fee for you work; the end result should be that the owner has a more valuable instrument, so your wallet should reflect the same!

    -Always remember to work within the limits of your skill set and the comfort of your mental abilities; we've all got enough stress in these challenging times...feel free to call the shop if you want to chat it up more candid offline or get a facetime link going.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Question: Is the neck problem due to a bowed neck or does it indeed need a neck reset? You will have to determine which is the case here.

    I have only seen a small handful of Gibsons from this period that had a neck angle problem. Bowed necks are more common.
    If you determine that there is a neck angle problem, you can go to the violin repair world and look up "slipping the neck block." We generally avoid this procedure in the fretted instrument world, but if the back indeed has to come off, it may be the most practical solution.

    I have made temporary molds from rigid insulation board, and inserting shims when necessary to spring sides into shape. I have yet to try it on a mandola or an A model mandolin, but I've used the technique successfully on a few flat top guitars. James' jig is great, but a temporary mold may work for a one-shot deal like an H-1.

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    Registered User sunburst's Avatar
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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    No need for anything fancy, but a jig will almost certainly be needed to realign the rim to the back. Both of these (mandolin and mandola) were made quickly by me in the shop using wood scraps. Both have been used for several instruments and both work just fine.
    Click image for larger version. 

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Click image for larger version. 

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    Here's how it works. I made little shims from cut-offs from mandolin sides and blunted a bunch of wood screws. Put the instrument in the form against the corck-padded rest, apply pressure with the shimmed screws wherever needed (drill for new ones if needed), "squeeze" the rim into compliance, glue and clamp.

    (BTW, I just set this up for demonstration purposes. If the back was actually being clamped for gluing I would have lots of clamps and probably cauls. It would be hard to see the form then.)

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    Registered User sunburst's Avatar
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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Due to the shape and size of the rim and head block, I doubt if slipping the head block will work, and if it does, something will have to be done to reestablish flatness of the back of the rim. I think it would be easier to simply reset the neck... but if my read of the OP is correct, the neck angle is not the problem.

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    I will assume a plain, old-fashioned warped neck unless I hear otherwise.
    They are a common problem on the old Gibsons, sometimes caused by neglect, or long time storage under tension, and sometimes by overstringing the instruments.
    Many of the off the shelf mandola sets will overstress an old Gibson mandola. Again, 12 -20 -32 - 48 or 50 works well on these instruments.

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    A few clarifications:
    The top brace is not loose(it has been reglued previously).
    My plan to remove the fingerboard & plane the neckshaft is to correct excessive neck upbow, not a low bridge, or poor neck angle.
    The back has already been off, has been poorly reglued/misaligned, and is partially loose. I can see evidence inside, of polyurethane(Gorilla) glue(curses, curses).
    I have a sides to back alignment jig, ala Frank Ford, have used it many times.
    Thanks all for your very helpful suggestions: The small x-brace is very good.
    The current owner is a local store for whom I do repair work: they bought it from a walk-in. I think it's unlikely they will spring for the hefty repair tab. I may have the option of buying it at near cost, and making the repairs on spec. But, all together, it would be close to market value(as far as I can tell).
    I'll keep you all posted.

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    Registered User j. condino's Avatar
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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Any sign of previous Gorilla Glue or epoxy is a deal breaker for me.

    Possibly the greatest single day in my 40 years of building and repairing instruments was the day I learned to politely smile, then hand the instrument back to the owner and say, "No thank you."

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Might be a good "keep you busy" project if your personal work situation is slow.

    I just pulled the back off a Goya 12-string guitar, pulled all of the excess lumber out of it, re-designed the bracing, and put it back together. Total cost: $150 for the instrument, $60 for shipping, and another $40 or so in wood, fretwire, and bone. I think it will turn out to be a better guitar than my old D12-20. If not, I can still sell it and get paid for some of my labor.

    After a long time of passing on "fix up and sell jobs," I've been eyeing an old Gibson oval hole that I can fix up and sell and make a reasonable portion of my ideal labor rate. While I might not make quite as much as I would like to, I can still make a profit and keep busy.

    I too generally avoid instruments that have Gorilla or epoxies in them, but if the back was glued with yellow glue or is already partially loose, you might be okay.

    Or if you've always wanted a mandola for yourself, it might still be a good project.

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    Default Re: 1914 gibson H1 mandola sagging top, and bowed neck

    Quote Originally Posted by rcc56 View Post
    ....if you've always wanted a mandola for yourself, it might still be a good project.
    +1

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