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Thread: Truss rod: Too tight? And still a string-ward bow.

  1. #1

    Default Truss rod: Too tight? And still a string-ward bow.

    On this first F5 I built I used the Siminoff method for the truss rod: Ace Hardware welding/drill rod with threads cut in, bent to an "L" at the body end and insert down into a hole in the neck base, drinking straw over the middle and a filler piece glued on top. On the peghead end I used a brass washer that I flattened on top. However--and here's the kicker--I used a plain ol' brass nut. I did NOT use a flared end nut. In all honesty I have never messed with the truss rod in the two years I've been using this mandolin, because by "using" I mean learning scales, chords, techniques (chop, etc.) and the absolute basics. I always has kept in tune fairly well and sounded--to my untrained ear--okay.

    In preparing to radius the fingerboard I removed all of the frets, removed the strings and I put a straightedge on the fingerboard. With the strings removed I noticed a significant upward (i.e. toward the strings) bow on the fingerboard. The first two fret slots on either end are level but then beginning around the third or fourth fret slot at each end it starts to dip. There is a significant dip in the middle of the fingerboard.

    I acquired an actual brass flared nut. I removed the old nut. (It actually spun freely, indicating it was never really tight to begin with...) I placed on the flared nut and began to tighten in order to pressure the neck in to flattening out the fingerboard. As SOON as it got some grip against the washer, as I tightened the neck would groan. I checked the fingerboard; exact same upward bow. I ignored the neck's squeaking/groaning noises and tightened again. Checked...still upward bow. I did this a couple more times every time with the same result until I just gave up and completely loosened the nut to relieve the pressure.

    I'm not sure what to do now. The fingerboard itself is uniform in its thickness all the way around, so there is definitely a bow in the neck. But adjusting the truss rod nut seems to have absolutely no effect. How much can/should I tighten this thing? Or perhaps the way I set up the truss rod it simply doesn't work the way it should? Would appreciate everyone's thoughts.

    Thanks.
    -Mark

  2. #2
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Well, don't tighten the truss rod again, at least not right now. If you strip the threads, you will have a nightmare on your hands. I'd suggest making a caul of some sort to hug the back of the neck. A large stiff v-grooved thing would work. And some padding in between that and the neck. And then a stiff straight board for the fingerboard side. Now you have a sandwich. Clamp that all together and let it sit over night at least. Then snug the truss rod nut up. Don't tighten it to try to bend the neck, just up snug. See if that holds when you take the sandwich apart. Things will improve after you refret, but trying to get the truss rod nut to do all the work isn't wise. It's even worse than trying to raise the bridge under full tension.

  3. #3

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Quote Originally Posted by putnamm View Post
    How much can/should I tighten this thing?
    I'm no luthier, but my two cents is that I snapped a truss rod on a Gibson once, in my back-in-the-day starving-musician attempt to lower the action my answer is "not as much as I did!"

  4. #4
    Teacher, luthier
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    If you believe that your truss rod is not functioning, you can 1] make sure there is enough thread on the rod to keep the adjustment nut from bottoming out, and add a washer if necessary, or 2] plane and re-fret the instrument. There are other techniques that will work, but most involve removal of the fretboard.

    There is another technique that does not involve major carpentry that I sometimes use that can pull some necks into position, but I am not going to publish it here. That is because if it is not done with extreme care, it can cause permanent and drastic damage to the instrument; and someone is sure to try it, mess it up, and end up with a broken instrument.

    You can pm me if you wish to discuss it further.

  5. #5

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Thanks for th suggestions. I am giving Dale's suggested method a try tonight and will share the results.

    I also imagined it may be possible that the neck is too "beefy?" I used Siminoff's drawings to make templates for the neck shape at various points and did my best to stick to those. But I suppose it's possible--being maple--that the rod just isn't strong enough to correct that much wood?

  6. #6
    Adrian Minarovic
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Here re few questions that come to my mind...
    How deep did you install the trus rod? Too shallow installation will reduce effect of truss rod.
    Did you use the Siminoff reverse curve? The curvature with both ends close to fingerboard and center the deepest is less effective than either straight rod deep in the neck or curved rod with ends deeper than center.
    How long was the straw on the rod? Should go pretty much from one end to the other so the rod isn't glued in anywhere. Otherwise it won't work.
    Did you clamp the filler piece tight against rod? Tight clamping against rod can have same effect as rod that is glued in.
    Did you lube the nut before tightening?
    Adrian

  7. #7

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Quote Originally Posted by HoGo View Post
    Here re few questions that come to my mind...
    How deep did you install the trus rod? Too shallow installation will reduce effect of truss rod.
    Did you use the Siminoff reverse curve? The curvature with both ends close to fingerboard and center the deepest is less effective than either straight rod deep in the neck or curved rod with ends deeper than center.
    How long was the straw on the rod? Should go pretty much from one end to the other so the rod isn't glued in anywhere. Otherwise it won't work.
    Did you clamp the filler piece tight against rod? Tight clamping against rod can have same effect as rod that is glued in.
    Did you lube the nut before tightening?
    The truss rod was bent downward, with the ends being deeper than the middle. Thus the filler piece was curved to fit it, so the filler piece is shallower in the middle. And yes, clamping was quite tight. As for depth...I don't have or recall the exactly measurements but to say that it was in the middle of the neck, generally speaking. The straw went from the angled bend on the body side all the way to nut. I did not lube the nut before tightening, no.

  8. #8

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Update: Yesterday I fashioned a caul from hard maple for under the neck that ran from the nut to nearly where the neck meets the body and padded it with scrap microfiber cloths. I also had a one-inch thick piece of hard maple, planed perfectly flat, that is longer than the fingerboard itself. I sandwiched the neck between these two, with the caul underneath and the flat maple on the fingerboard and clamped these with three C-clamps. The truss rod nut was completely loose. I let this sit overnight.

    This morning I tightened the truss rod nut just until I got the feeling that the wood would start complaining again. And I released the clamping pressure. Unfortunately, the neck bowed back in to its original position. I've attached a photo from the seventh fret position of the board, where the bowing seems to be at its deepest point, with a straight edge lying on the fingerboard surface and a small rule for reference. You will see that the amount of bow in the middle is about 3/64".

    The fingerboard itself is uniformly 3/16" thick. I had a thought that perhaps I could plane the bow out, but I think I would have to remove too much material. I would appreciate everyone's thoughts on this, particularly as I plan--once the fingerboard is truly flat--to radius the fingerboard.

    My next thought is to perhaps try rcc56's first suggestion of adding a washer, as I have plenty of room to do so. In the meantime if anyone has any additional suggestions I am certainly open to them.

  9. #9
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    My understanding is the frets themselves normally cause a bit of a back-bow. Martin used to correct string side bows by using larger fret tangs on a refret. Since your neck was Ok before you removed the frets, I think your problem may have more to do with that.

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  11. #10

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    I have made some gradual progress with the clamping method as I originally tried, over several days, but I'm nearing the point where I am uncomfortable with the amount of pressure I am putting on the neck...

    I measured the neck depth compared to Loar plans that I obtained after building this one, and it appears my neck maybe too thick. For example, the plans on the List show a neck depth (minus fingerboard) of approximately 18mm at the fifth fret. Mine is approximately 22mm. This differential seems to be consistent throughout the neck. I also measured the full depth (fingerboard and neck) at the seventh fret, and it was 27.5mm.

    1. Could this be the cause of my truss rod not functioning properly?
    2. Is reshaping the neck recommended? I have plenty of tools for the job included rasps and at least one spokeshave.

    The finish is just TruOil over a single coat of Transtint Dark Walnut

    Thanks.
    Mark
    Last edited by putnamm; Jun-03-2020 at 1:01pm.

  12. #11
    Registered User amowry's Avatar
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Do I understand correctly from your first post that there are currently no frets or strings on the instrument? If this is an instrument that you just want to be able to play yourself and you aren't trying to sell, then I would think you could just flatten the fretboard (with no tension on the trussrod), then refret. In fact, that's what I always do when I have frets removed, because it "resets" the neck to its original state, giving the trussrod a better chance of doing its job. The trussrod may work well enough to prevent the strings from backbowing the neck again, even if it doesn't work well enough to correct the existing bow.

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  14. #12
    Registered User amowry's Avatar
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    It does sound like the neck is thick, but that's a separate issue and more one of personal preference. Yes, the trussrod might be more responsive if the neck were thinner, but you'd also be losing additional stiffness in the neck.

  15. #13

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Andrew, thanks for the great feedback and questions.
    No strings or frets on the instrument at this time.
    This is the first mandolin I ever made, I made it just for myself to learn to play on. So no, there is no buyer to please or impress with it. I can do whatever I like with it.
    And while the neck is personal preference, I have no frame of reference for any of this including my preferences. I've never played another mandolin. So I don't know what I prefer.
    Because I intend to build more--many more, hopefully--mandolins in the future I'm using this one and only instrument I have in my shop to try and learn to do things the right way. I did, in fact, think about just sanding it down. I also intend to radius the fretboard. But there is a part of me that wants to treat this like a customer's instrument so I can learn.
    But I appreciate your vote of confidence and suggestion to tackle it head-on!

  16. #14

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Before you pulled the strings and the frets how straight was the fingerboard?

  17. #15
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    If the neck profile is to your liking, I would not advise changing it.
    And if you did change it, chances are good that it would not help the truss rod.
    And if you cut too deep and mess it up and hit the truss rod pocket, you would have to re-neck the instrument.

    Put a drop of oil on the truss rod nut, jig it up once more, and see if it will pull in.
    If not, remove the fingerboard, see if you can get the truss rod working.
    If not, you can either dig it out, and do whatever is necessary to fix it. Or replace it with a carbon fiber bar. Or straighten the neck as-is by planeing and/or heating, bending, and clamping it. Then put the board back on. If the rod still isn't working, you can re-install the board with just a few thousandths of back-bow.
    Last edited by rcc56; Jun-04-2020 at 9:47pm.

  18. #16

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    As a beginning builder and so far using metal or carbon bars for reinforcement, it occurs to me that if an adjustable truss rod is installed, it should at least be snugged up to counteract the weakened neck from cutting it in. Do you recall how you left the nut when you first built the mandolin? If loose, maybe that, sadly, made the neck more susceptible to bowing than would otherwise have happened.

  19. #17

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Quote Originally Posted by Parker135 View Post
    As a beginning builder and so far using metal or carbon bars for reinforcement, it occurs to me that if an adjustable truss rod is installed, it should at least be snugged up to counteract the weakened neck from cutting it in. Do you recall how you left the nut when you first built the mandolin? If loose, maybe that, sadly, made the neck more susceptible to bowing than would otherwise have happened.
    Parker, that's a good point. When I first approached the truss rod nut it was slightly loose. It wasn't spinning freely, but it also was not securely/snugly tightened up against the washer. So that could be a cause.

  20. #18

    Default Re: Truss rod: Too tight? And still a string-ward bow.

    Good news: After removing a uniform 4mm in thickness from the neck, the truss rod appears to be functioning now. The fretboard is dead flat with the truss rod tightened just to where it snugs up. No strings yet, so we will see what happens when they are added.

    Click image for larger version. 

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  21. #19
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    Default Re: Truss rod: Too tight? And still a string-ward bow.

    I hope that will work for you now, but if it still bows too much, one other option would be to do a compression fret job with EVO # 37053-230
    It’s got a thicker tang and would stiffen the neck considerably.

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