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Thread: Bowed neck issue

  1. #1

    Default Bowed neck issue

    Hi Folks, I'm restoring a vintage Harmony HG-165 mahogany guitar and I've run into an issue I wanted to run by the forum before I tackle it. I just did a neck set which looked perfect before and after glueing it in, but when I put on strings, the neck bowed up about 1/8 " at the 12th fret making the action uncomfortable.

    Now Harmony's of this era (late 50's early 60's?) have steel re-enforced necks and the amount of bow was a surprise. I'm using light gauge strings (12-53) and the steel re-enforcement should have kept the bowing from happening. That being said, I've heard some bad comments about harmony and the steel re-enforcements (someone referred to it as a used hack saw blade). The bow was significantly more pronounced on the bass side of the neck.

    I'm considering several possible approaches to deal with this. My initial though was to simply re-set the neck again at a steeper angle. That's a possibility, but there will still be too much bow in the neck for the guitar to play well. I also could shave down the bridge, but again, that doesn't solve the underlying problem and isn't what I'd prefer to do.

    My current thinking is to remove the fret board and see what's going on with the re-enforcement bar. Perhaps I can re-seat it or maybe replace it with a carbon fibre rod or similar stiffener.

    Does anyone have any experience dealing with this issue? I'd love to get some thoughts on the best way to deal with this and any insights into what I'm heading into.

    Thanks very much!

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  2. #2
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    Default Re: Bowed neck issue

    If you did your neck set correctly, the bowing neck must be addressed.
    Too bad you didn't pick up on it while the neck was out of the guitar, but that's the way it goes in the repair business.

    I don't have any experience with Harmony, but the "right" way to handle it would be the same on any guitar. Pull the board and see what's going on. It may be necessary to install new reinforcement. The choices are an adjustable truss rod, or a solid carbon fiber or hard maple or ebony bar. Conventional wisdom leans towards carbon fiber rather than hardwood, but there are thousands of wartime Martins and 'teens Gibson mandolins that are doing fine with ebony or maple reinforcements.

    I just happen to have a wartime Martin on the bench waiting for me to re-fit the neck. The ebony bar measures 3/8" in both width and depth, and extends from the outer edge of the dovetail to the nut pocket.

    My limited experience with carbon fiber has made me decide that if I use it again, I'll embed it 1/16" below the surface of the neck, and fill the remaining space with a hardwood [probably maple] filler strip. That's because carbon fiber doesn't sand or file well. Levelling a filler strip is easier on the hands, arms, and tools.

    If you're not jigged up to rout a pocket for your reinforcement, perhaps a friendly guitar maker can make the cut for you.
    I use a 2" x 5" 50 watt heat blanket from McMaster-Carr or MSC Industrial, plugged into a Harbor Freight router speed controller to pull fingerboards.

    If I have to reinforce another neck, I might try an ebony bar, possibly made from two pieces laminated vertically with hide glue. A striped ebony fingerboard blank could be one affordable choice of material.

    However you decide to go about it, I wish you good luck, and hope the board comes off nice and cleanly.
    Last edited by rcc56; Oct-08-2019 at 6:42pm.

  3. #3
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    Default Re: Bowed neck issue

    I agree. If the neck angle is right don't change it. In addition to the good advice given above. A thicker fret board can help too. Though it will change the feel of the neck.

  4. #4

    Default Re: Bowed neck issue

    rcc56, Thanks for the excellent, detailed advice! Very much appreciated. Yes, I'm convinced that the neck angle is correct. I unstrung it and checked and, as I expected, when unstrung, it was right on the money. Clearly the reinforcement rod is't working correctly. I love old Washburn parlors and I've had 1890's guitars not need a neck re-set because of their steel bars (a bar perhaps 1/16th" X 1/2" set vertically in the neck).

    I'll definitely go ahead and pull the board. I'm very interested in seeing what's going on inside and this may be an excellent chance to try out a carbon rod or ebony bar. I've never tried that but can see it would be a valuable skill in the vintage restoration business. I don't have the correct heating pad for a fingerboard, but I do have an old neck heater for heat bends that will easily do the trick. I've got an LMI heater control I've used with a bridge heater but it never seems to heat properly. Perhaps I'll try the Harbor Freight router speed controller you spoke of.

    I'm not set up for routing a slot, but probably ought to figure it out. I'll post pics as I go along and would appreciate you ongoing thoughts.

  5. #5
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    Default Re: Bowed neck issue

    Several things to consider: how thick is the fingerboard? Could remove frets and level the fingerboard, re-cut fret slots, and refret. This would be the simplest and easiest process but it depends on how flexible the neck is. It could be hide glue holding the board on but it also could be like the glue used in exterior grade plywood, I forget the name at the moment. Hide glue can be separated but the other one not so much without pulling wood apart. There is a risk in removing the fingerboard, if it comes off nicely you are golden but sometimes fingerboards and necks come apart in such a process if the glue doesn't let go. You might consider just replacing the fingerboard from the beginning, and go from there. Once the board is off you can dig out the reinforcement bar (a thin saw cut right along both sides of the bar will allow you to break out the bar pretty cleanly (usually), be careful to cut only as deep as the bar (don't cut through the back of the neck). Potentially lots to think about.

  6. #6

    Default Re: Bowed neck issue

    1/16x1/2 does sound like the ‘used hacksaw blade’! Anyway, any reinforcement isn’t going to work unless it is still in really good contact with the bottom and top of the slot (if it’s a vertical web). Wood shrinkage or rust may have given it some room to move. Something that grasps the wood on the sides of a slot should be better. Anyway, you don’t need a router to make an accurate slot, IMHO, just a pullsaw, a tenon saw or something like that. Make parallel cuts along a straightedge fence and snap out the waste with a chisel. The old-fashioned manual router is perfect for a cleanup at the bottom.

  7. #7
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    Default Re: Bowed neck issue

    I have had weak glue joints cause a neck to bow and simply removing and regluing helped. You can also try refretting with oversized tang frets which will help the bow. I have done that with old Martin bar frets and it worked great. Lots of good ideas here. I heat the fingerboard with a 100 watt bulb in my bench light. DON"T walk away and watch it. I heat a small area at a time and work it loose, then move on. Be sure to protect the body when doing the extension. I use cardboard wrapped in foil.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

  8. #8

    Default Re: Bowed neck issue

    Well it's been quite a journey so far. I used the neck heater to heat the finger board and was making slow, but steady progress when things went downhill around the 7th fret. The glue would not separate and the fingerboard began to crack.
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    I managed to get past that joint, but it cracked again at the next fret. I've managed to work around the issue for the moment, but ultimately decided to add moisture and let it sit over night and try again today.

    I've got to say, I'm surprised at the difficulty. I've pulled countless fingerboards and never had a problem before! Usually heat will soften the glue and gentle work with a blade separates the fingerboard easily.

    Re: Richard500's comment "1/16x1/2 does sound like the ‘used hacksaw blade!" I was referring to the steel bar in the vintage Washburn Parlor guitars of the 1890s, not the steel bar in this guitar.

    I'd hate to have to replace the fingerboard. So far I'd say it's still salvageable, but I see the fret slots are pretty deep so this issue may continue. I'll let you know how it works out.

  9. #9
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    Default Re: Bowed neck issue

    Sounds like you are dangerously close to damaging the neck by trying to save the fingerboard. If you have any doubts, sacrifice the fingerboard and save the guitar.

    $30 or so for a fingerboard, less than $10 for frets and inlays, 1 hour of labor to fit and glue it, half an hour to install the dots, and 3 to 5 hours to fret it. That's a lot less work and money than a complete neck replacement.

  10. #10

    Default Re: Bowed neck issue

    The saga continues! After going back to my old tried and true way of heating the fingerboard with a clothes iron and giving it time to get down to the glue, I was able to very carefully remove the fingerboard with no more damage though it was slow going!

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    Upon inspection, I found a couple issues: The fingerboard itself seemed to have a flaw at the point where it split. The grain pattern takes a steep dip which may have made the entire area weaker. There also appears to be some additional damage around that area that wasn't caused by the removal.

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    I'm not sure if this was an original defect or if the fingerboard had been removed previously. This guitar did appear to have had a previous neck re-set and the bridge had been replaced with a Martin style belly bridge with through the top pin holes, but I didn't get the sense that the fingerboard had been removed.

    Closer inspection of the steel rod proved quite interesting. It actually sat about 1/16th below the glue surface of the neck and I was surprised to find that it was not glued in place and came right out. Between the fingerboard issue and the unglued steel bar, I could imagine enough give to easily account for the extra bow in the neck when under tension.

    I removed the bar and saw a couple curious things. It is slightly bent sideways.

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    It's clearly too thick to have been bent while inside the guitar. Would this have been intentional or an accident? I also saw that there was rust on the top and o the first 1/4" or so of the sides.

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    I'd appreciate everyone thoughts on how to proceed. I'd propose glueing the fingerboard damage with epoxy so it won't come loose if the board needs to be removed again. I also assume I should glue in the steel bar and based on a comment from rcc66, I'll add a thin wood cover over the bar to bring the slot up level and keep everything in place.

    I'd appreciate any thoughts, particularly about the bend in the bar.
    Last edited by Ginridge; Oct-09-2019 at 2:34pm.

  11. #11
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    Default Re: Bowed neck issue

    The bent bar is probably just shoddy workmanship, as is the unglued bar sitting 1/16" low with nothing to cover it. Whether that happened at the factory or from a later repair attempt, nobody knows. I would guess that your bow came from the loose bar, which rendered it structurally useless.

    Clean everything up, insure that the channel is of uniform depth, and reassemble with a stiff piece of hardwood on top of the bar. If the bar has any significant vertical flexibility, replace it with something stiffer. Get everything good and snug. I would cut out any damaged wood from the back of the fingerboard and graft new wood in-- glue alone has no structural value. I might [or might not] devise a clamping method to induce a few thousandths back-bow into the neck when gluing the fingerboard back on, depending on how stiff the neck feels.

    Remember that strength is the goal here. You don't want to have to re-do this next year.

  12. #12

    Default Re: Bowed neck issue

    Amen! Do it once, do it right!

    Thanks. That's sound advice all around (no pun intended ...)

  13. #13

    Default Re: Bowed neck issue

    I assume I should glue in the steel bar. Is that right? Is hide glue acceptable? I'll do that and put in the cap strip, then and sand level before putting on the fingerboard.

  14. #14
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    Default Re: Bowed neck issue

    Hide glue does not bond well to metal. Epoxy is the most common choice for wood to metal.
    I would recommend hide glue for the fingerboard to neck joint.

  15. #15
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    Default Re: Bowed neck issue

    [Deleted due to redundancy.]
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  16. #16

    Default Re: Bowed neck issue

    As suggested, I cleaned out the routed slot (not much to do since the steel bar just sat in there) and it was already a good fit.

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    I mixed up a batch of stu mac slow cure epoxy and lightly covered the slot and the steel bar fitting it in and cleaning up any squeeze out.

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    As it set, I clamped it to create an ever so slight back bow.

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    I also inlaid a thin strip of mahogany to bring the recessed slot up to level. That's where we are at the moment. I'm off for gigs for the next 4 days, but once I get back, I'll complete the repairs on the fingerboard, sand and level the top of the neck then re-glue.

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  18. #17

    Default Re: Bowed neck issue

    Thanks for the advice everyone. Things have progressed nicely. I was able to glue damaged fingerboard, then cut out the damaged section from the back and and inlay new Indian Rosewood for strength and stability.

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    I repaired the tear out on the neck mostly using the original pieces then sanded it flat.

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    I glued the fingerboard back on using fish glue and large rubber band strips.

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    The neck turned out very well with the fingerboard well aligned.

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    Most of the plastic pearled markers came out in the process, but I plan to replace them with real pearl dots.

    I leveled the frets, cleaned upset fingerboard and removed a couple high spots in the previously damaged area of the fingerboard then did a test string up to see if I needed to replace the saddle. Happily, the neck angle turned out to be right and the action was good right out of the box but I'll do a bit of tweaking after I deal with finish touch up.

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  19. #18

    Default Re: Bowed neck issue

    After quite a bit more fine tuning, I got the action set to Martin specs at the nut and 12th fret. The high E, B and G string slots had all been cut too deep in a previous repair so I did the bone dust and superglue trick to bring all three up a bit. Inlaid the fingerboard dots and added side dots and a bone strap pin then started to finish touch up. Wet sanded up to 800 grit, then applied a light french polish to seal a few bare spots and give it a nice look.

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    It plays very nicely and has the rich bright tone you'd expect from 60 year old mahogany. Thanks to everyone who shared advice. I learned a lot on this one!

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