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Thread: Bow in bowl back neck (joint?)

  1. #1

    Default Bow in bowl back neck (joint?)

    My bowl back (1912) has a forward bow in the neck. I believe it's caused more by years of tension on the neck joint than an actual bow in the neck itself. The first photo shows a slight gap/bow with a straight edge that does not extend over the neck joint frets. The second photo includes all frets, with the straight edge extending to the end of the fret board, and the bow is more pronounced, leading me to believe it's more of a neck joint issue. There is no separation occurring around the neck.

    I tried clamping the neck down to a flat surface (granite), with the clamp situated around the neck joint area, and wrapping it with a heating pad. Did that for about two weeks, turning the heat on for a couple of hours several times a day. Seemed better, but now it appears to be like it was before.

    I have seen where people will apply pressure, but actually bow the neck back a bit (creating a back bow, in hopes of ending up with no bow). Is that something you've done, or would recommend? If so, how is that done?

    I don't really want to remove the fret board and remove wood from the neck underneath.

    Thanks!

    JimClick image for larger version. 

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  2. #2
    Teacher, repair person
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    Default Re: Bow in bowl back neck (joint?)

    I can't tell for sure from the pics, but it looks like this mandolin may have had bar frets. That might affect the way I would approach this kind of repair.
    What is the width of the fret slots? You can check it with feeler gauges.

    At any rate, I can't say anything for sure without the instrument in-hand, because it is necessary to project what would be necessary to end up with geometry that will result in both reasonable action and sufficient bridge height.

    If it is a bar fret instrument, a compression fret job with slightly oversize wire might straighten the neck. Finding bar fret wire in mandolin width is a problem. You would probably have to find someone to roll some for you. Note: I have not had long term success using the compression technique with T-fret instruments.

    If it is a T-fret instrument, the board can be planed and refretted. If the plane of the fingerboard needs to be tipped back slightly to provide good action with sufficient bridge height, you can take more off the nut end than at the sound hole end. If it needs to be tipped back more than a little, this will not provide you enough without thinning the board too much, and more drastic techniques will be necessary.

    Some people may suggest a heat-press technique. You have already tried a variation on this. My experience is that the heat press technique will sometimes work as a temporary solution, but over the long term, the bow will come back, sooner or later.

    If the bow is extreme, the fingerboard can be lifted, the surfaces cleaned, and clamped into a very slight back-bow using fresh hot hide glue and an appropriate caul. Tricky, but do-able. Depending on the shape and severity of the bow, it may only be necessary to lift the board from the nut to the middle of the neck. In other cases, the board may have to be lifted from the nut to the body joint.

    Before you choose your repair techniques, you are going to have to find a way to determine that once the fingerboard is level, the neck angle will be sufficient to provide reasonable action in conjunction with bridge height that is sufficient to result in good tone. That will require understanding of instrument geometry, an ability to estimate accurately, and some inventiveness to help you measure and estimate.

    If the neck angle is not sufficient, that's a worst-case scenario. In that case, you would be looking at either the possibility of a neck set or the installation of a tapered shim under the fingerboard. Then you would have to decide whether or not you wanted to put that much work into the instrument. Hopefully, that will not be necessary.

    With any luck, a plane and refret will take care of it. If not, welcome to the world of learning the deeper elements of the craft.

    If you're anywhere near southeast Tennessee, I would be happy to look at the instrument and give you my best advice on how to proceed.

  3. #3

    Default Re: Bow in bowl back neck (joint?)

    Above advice covers the bases: you can add or subtract, or replace, but the one really difficult thing is trying to reset the neck. I would only add that you measure the deflection with and without full string tension using a good straightedge and feeler gauges, because there’s always a chance that the neck joint has a little play, or that the neck itself can bend. This would make your other efforts fail. Yes, learned this at least twice.

  4. #4
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Bow in bowl back neck (joint?)

    Jim, we were just discussing bowlback mandolin fretboards in another conversation here.

    That's why I enjoy the Cafe vibe of the MC.

    It's like you're in one conversation and you overhear another conversation at another table and.....


    That is a substantial fretboard.

    Along with the neck / bowl joint--and date--my hunch would be American made. Is that correct?

    It is an interesting, if frustrating, problem, because for all the (many) bowlback neck problems I have seen,
    I have seen very few with actually bowed necks such as yours.


    In my experience, typically if the neck is out of whack it is due to some slight, but meaningful, rotation at the neck block / bowl area likely due to
    some top sinkage north of the soundhole. It doesn't take much.

    Folks often call it a "bowed neck" as the fretboard attached to the top usually stays in alignment with the top. It appears bowed.


    Yours, indeed, looks like it is actually bowed.


    I'll leave proper repair advice to the experts here.

    I know what I'd do given how thick that fretboard is....but it's super true:
    the subtle geometries of action, bridge height, string break angle, not to mention the art of fretwork are crucially important.


    Please post some more photos of your mandolin, if you will, for we bowlback wonks.

    And keep us updated on your repair process!


    I hope you work things out so you can play this (again?) merrily.


    Mick
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  5. #5

    Default Re: Bow in bowl back neck (joint?)

    Thanks so much to all of you for the detailed, experienced responses! I'll answer all your questions below, and include some more photos.

    it looks like this mandolin may have had bar frets. That might affect the way I would approach this kind of repair.
    I believe they are bar frets, but I've included a photo of them below since I'm just a rookie.

    What is the width of the fret slots?
    Per my measurement, about (they aren't all consistent) .030 in. or .76mm.

    Finding bar fret wire in mandolin width is a problem.
    Glad you said that. I was having no luck. Neither the "narrow/low" nor the "medium/medium" seems like a fit. Total height of the existing frets is about .094 in. Width at the bottom is about .029 in., and width including the prongs is about .040 in. Im willing to switch to a different style (t?) if needed. Id like to keep this as original/authentic as I can, but might have to compromise for the frets.

    If you're anywhere near southeast Tennessee, I would be happy to look at the instrument and give you my best advice on how to proceed.
    Thanks for the kind offer! But I live in Tulsa, OK

    Along with the neck / bowl joint--and date--my hunch would be American made. Is that correct?
    Yes. It's made by Harwood, in about 1912, and I believe their location was Kansas at the time.

    Please post some more photos of your mandolin, if you will, for we bowlback wonks.
    Posted some more photos for you below.

    I found this in rough shape for $80 in an antique shop. I'm trying to do all repairs myself as a learning experience, so I can make mistakes now that I can learn from. Time spent is not an issue because I just retired and i love learning/doing new things! My goal is to do what i can, and though I hope to make it decently playable, I'm not expecting great sound. For that, I'll play another mandolin. But I do LOVE the idea of bringing sound and songs back from an instrument that someone was first playing over 100 years ago!

    JimClick image for larger version. 

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  7. #6
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Bow in bowl back neck (joint?)

    Thanks, Jim.

    A Harwood, you say.

    Have you had a look at the thread here on Harwood mandolins and guitars?

    I have a special place for Harwood mandolins. I own a Harwood with a mahogany bowl. Super curious mandolin.

    Anyhow, your Harwood keeps the Butch Hancock inspired "no two alike" streak going.
    For all the Harwood mandolins collected in the thread, we've yet to see two that are alike, as in exactly the same.

    The top edge banding on yours is special for a Harwood.

    The "Harwood" linlay sort of complicates my non-professional strategy for de-bowing.


    To be sure....if you get this neck 'playable' and set this up with some Dogal Calace Dolce strings....you'll be getting great sound out of it.


    Mick
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  9. #7
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    Default Re: Bow in bowl back neck (joint?)

    Yes, those are bar frets, and it looks like Harwood had some sort of technique for serrating the wire that I have not encountered before.
    There is no commercially available fret wire that will work in this situation.
    There are a couple of solutions. None of them are easy, nor are they recommended for a novice.

    1. Partially fill the fret slots with ebony strips, grind them flush, recut the slots to .020" - .022", then plane and re-fret with T-frets.
    2. Contact TJ Thompson and see if he will roll some bar fret wire for you. The minimum size will have to be .029" or more. The wire will have to fit tightly. Plane and refret. Installing and profiling bar frets requires at least double the labor time of a standard fret job. For an inexperienced person, double the labor time again.
    3. Pull the board, true up the neck by planing it or heating and clamping it into a ~.015" back bow, and install a new fingerboard. If necessary, the new board can be tapered to provide the geometry necessary for good bridge height.

    Believe it or not, #3 will probably take less time then the other methods.

    I strongly recommend hands-on training with a qualified pro for this one. That probably wouldn't be available for free.
    Last edited by rcc56; Jun-26-2022 at 11:55pm.

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  11. #8

    Default Re: Bow in bowl back neck (joint?)

    Mick, thanks for that input. I checked out that Harwood thread, and I'm loving it! With the options described above, I think I will find a way to keep moving forward. And, if I manage to make this puppy sing again (thanks for the string suggestion!), I'll be sure to let the group know!

    Jim

  12. #9

    Default Re: Bow in bowl back neck (joint?)

    RCC56, thanks again for adding even more info and options! Your great experience and clear teaching is extremely valuable, so I really appreciate your taking the time on this! Only one question and I'll stop bugging you. If I were to try to get a new fingerboard, do you think I'd have any luck finding one with the slots precut?

    It appears that the fingerboard scale length would be just over 13" (13 1/16" or 13 1/8", measuring to the front of the indentation left by the original bridge). I looked at Stewmac, and their mandolin boards have a longer scale length.

    Jim
    Last edited by jimcarrington; Jun-27-2022 at 4:21pm.

  13. #10
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    Default Re: Bow in bowl back neck (joint?)

    ..

  14. #11
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    Default Re: Bow in bowl back neck (joint?)

    There are several places that will pre-slot a fingerboard for you. My first suggestion is Luthier's Mercantile: www.lmii.com

    You don't have to buy the top grade. A grade 2 Indian ebony board will be fine. You can dye it if you like. Measure your scale, then give them a call them and ask them to slot it to your scale. That's all there is to it. They will deliver the board in a timely manner. If you need fretwire, bone, position dots, or anything else, you can get it at the same time.

  15. #12
    Registered User Tavy's Avatar
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    Default Re: Bow in bowl back neck (joint?)

    Sorry for being late to the bowlback party!

    Given the thickness of the board, I would leave the angle as it is (it's not going to change much now), and level the board in place - looks like you don't need to remove more than 0.5mm or so from the nut end to get things level? Even 1mm from that end would probably work out on that one.

    Then you're either looking at putting those old frets back in (there will be a lot of levelling to do afterwards as they'll stick up a lot where the board has been sanded down), or as suggested above, shim the slots with ebony veneer and put new fretwire in. The last option is not nearly as hard as it sounds, just be sure to put all the shims on the same face of the slots, and double check what effect that will have on nut position - if you're lucky shimming one particular face will leave the nut in a decent spot for correct intonation. You will need to run a fretting saw through the slots after shimming BTW, probably deepen some of the slots too.

    That sure is a pretty bowl though!

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  17. #13

    Default Re: Bow in bowl back neck (joint?)

    Thank you so much Rcc56!!

  18. #14

    Default Re: Bow in bowl back neck (joint?)

    Thank you Tavy!

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