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Thread: Neck reinforcement vs a truss rod

  1. #26
    Registered User j. condino's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Well....they've been making upright bass necks for 400+ years with at least a gigantic 42" string length and occasionally in the 44"+ range with an average of approximately 300 lbs of tension. Nobody uses an adjustable truss rod on them & never have, but almost all contemporary builders use rigid carbon fiber rods under the fingerboard. Bass players are far more fussy about fingerboard relief and have a much better understanding of it than almost any mandolin player I have met.
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  3. #27
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    Default Re: Neck reinforcement vs a truss rod

    Quote Originally Posted by j. condino View Post
    Well....they've been making upright bass necks for 400+ years with at least a gigantic 42" string length and occasionally in the 44"+ range with an average of approximately 300 lbs of tension. Nobody uses an adjustable truss rod on them & never have, but almost all contemporary builders use rigid carbon fiber rods under the fingerboard. Bass players are far more fussy about fingerboard relief and have a much better understanding of it than almost any mandolin player I have met.
    While I agree with this, I think you would need a pretty huge truss rod to be effective on an upright bass. That may have influenced builders decisions.

  4. #28

    Default Re: Neck reinforcement vs a truss rod

    Quote Originally Posted by j. condino View Post
    Well....they've been making upright bass necks for 400+ years with at least a gigantic 42" string length and occasionally in the 44"+ range with an average of approximately 300 lbs of tension. Nobody uses an adjustable truss rod on them & never have, but almost all contemporary builders use rigid carbon fiber rods under the fingerboard. Bass players are far more fussy about fingerboard relief and have a much better understanding of it than almost any mandolin player I have met.
    This gets to the question I wish I knew enough geometry, math and engineering to ask: What is the magic in such a design? Is there some angle here that ends up with the neck being in a central axis, not being pulled up too much and not being pulled down (at all?). I keep trying to see how the neck angle relates to something I can understand - levers and fulcrums - but as I say, I cannot get to the simple resolution.
    There's a reason for the general neck angle for the Gibson style mandolin. There's a reason for the general neck angle in a Guarneri violoncello. There's a reason for the neck angle of Condio's bass. Yes?

  5. #29
    Registered User John Bertotti's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    I have a cf bar. I think it was 3/8” tall and a bit narrower. I need to measure it because I am not positive. But my question is what size do you use? Do you mount it low in the neck or just under the fret board in the neck?
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  6. #30
    Registered User sunburst's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    I usually use 3/8" by 1/8". It fits in a kerf from the table saw so installation is easy. I set them just under the 'board so I don't have to fit a cover stick.
    Usually, though somewhat dependent on installation, we simply rely on the stiffness of CF to control neck movement, so any depth is about the same. In reality, CF is more resistant to stretching than to compression, so if we can set the rod deeply in the neck and securely lock the ends we get more overall stiffness in the neck. Getting ends locked any better than setting the rod in epoxy is too fiddly for me, so I take the easy route.

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  8. #31
    Registered User John Bertotti's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    I suppose a person could pin the end but it seems that is probably unnecessary.
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    Registered User lowtone2's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Quote Originally Posted by j. condino View Post
    Well....they've been making upright bass necks for 400+ years with at least a gigantic 42" string length and occasionally in the 44"+ range with an average of approximately 300 lbs of tension. Nobody uses an adjustable truss rod on them & never have, but almost all contemporary builders use rigid carbon fiber rods under the fingerboard. Bass players are far more fussy about fingerboard relief and have a much better understanding of it than almost any mandolin player I have met.
    Because we don't want it to sound like a banjo or make our fingers fall off.

  10. #33
    Registered User John Bertotti's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Having never used cf will a standard five minute epoxy be the good?
    My avatar is of my OldWave Oval A

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  11. #34
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    Default Re: Neck reinforcement vs a truss rod

    I would use a longer drying time epoxy, it will be much stronger. I use 2 ton epoxy, there is better stuff out there, but this is available here.
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  13. #35
    Registered User John Bertotti's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Will do my stuff is good for 3900psi 5 minute epoxy. I’ll order some longer stuff.
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  14. #36
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    Default Re: Neck reinforcement vs a truss rod

    John--How did your cf reinforced mandolin turn out? Did you use a 3/8 X 1/8 rod as mentioned by Sunburst? i wonder if there is a standard size. Looking on Amazon, I found rods that are square in cross section and also hollow. I had a friend tell me that Dave Cohen told him that a "half I beam" would be good. I wonder what that would be and where you might find that. I'd appreciate recommendations from those of you (J. Condino?) who use carbon fiber reinforcement for necks. Thanks! Here is a link to that rod i mentioned: https://www.amazon.com/cncarbonfiber...dp/B08SW2Z1PT/

  15. #37
    Kelley Mandolins Skip Kelley's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Woody, I got mine off of eBay. Here’s the link…https://www.ebay.com/itm/123283332877?var=423686175223
    I put it in the neck and leave room for a wood filler strip. I hope this helps.
    God bless, Skip

  16. #38
    Registered User j. condino's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    J. B. Alred's company, Dragonplate manufactures all of their carbon fiber in the US and supplies almost all of the other people in the nation who then sell it for a highly inflated price.

    https://dragonplate.com/solid-carbon...SAAEgJLcfD_BwE

    Don't overthink it.

    Look through the 3000 different choices that Dragonplate offers, pick one, and glue it in.

    It is a tiny little mandolin, not a space ship.

    'You got this homie!
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  17. #39
    Registered User John Bertotti's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    I hate to say it but I never used it. It was 3/8” square.
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  18. #40
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    Default Re: Neck reinforcement vs a truss rod

    Like James, I prefer the use of CF reinforcement rather than a truss rod. The metals from which truss rods are made have densities in the 7-8 g/cm3 range. They are replacing wood which has a density typically in the 0.5-0.6 g/cm3 range. So regardless of how you make the metal riod, you are adding mass to the neck, and that affects the balance of the instrument. It is even worse if you are using a two-way adjustable rod, Even with a "one-way" rod, you are adding ~30 grams (~ 1 oz) to the head end of an instrument which is already burdened by ~160 grams (+/-) of tuner mass.

    CF composite typically has a density of ~1,7 g/cm3. Just measured it on a leftover piece of Allred rod. So if you just bury some CF in your neck you are still adding a bit of mass to the head end of your instrument, but not nearly as much as you are adding with a metal adjustable rod + its adjustment hardware. You are adding a few grams, as in ca 3-5 grams vd the ca 30 or more grams from an adjustable metal truss rod. And, if you use a hollow CF shape. such as Allred's D-tube, or a hollow rectangular beam, you are actually Decreasing the overall mass of the neck assembly. And, you can extend the CF partway into the headstock, which reinforces the fragile hyoid area of the neck/headstock. By contrast, the truss rod slot only makes the hyoid area MORE fragile.

    I also posted on this in another recent thread. I'm feeling lazy this morning, so see my post #8 in the recent truss rod and carbon fiber thread.

  19. #41
    Registered User sunburst's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    My adjustable rods weigh 23 grams, my filler stick is spruce. I haven't done the math, but replacing maple with spruce offsets the addition of steel very slightly. Given a choice, I would prefer to reduce the weight of the tuners!

  20. #42
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    Default Re: Neck reinforcement vs a truss rod

    John, as I remember it, you ground away part of the rod to reduce mass, Is that still the case?

    Re replacing the maple with spruce: I would emphasize the "...very slightly...." in your post. In my experience, densities of maple samples (with the exception of birdseye) have varied from ~0.54 g/cm3 to about 0.61 g/cm3. Assuming you are using sitka spruce or Adirondack spruces, the densities I have measured have been in the range 0.43-0.5 g/cm3. If you are using Engelmann spruce, it is more typically in the range 0.38-0.43 g/cm3. I wouldn't be surprised to see samples of any of those species with densities outside those ranges.

    Regarding lower tuner mass, I am ever hopeful, but so far I have only seen the trend go the other way. I had some older samples of golden age tuners with masses of around 134 g (sans grommets). I also had a more recent set with a mass of 150 grams. Some Rubners I have used were up around 160 grams or slightly more. So far, I think tuner manufacturers are seeing things like thicker plates and other "robust" parts as a path to greater durability and quality.

  21. #43
    Registered User sunburst's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Quote Originally Posted by Dave Cohen View Post
    John, as I remember it, you ground away part of the rod to reduce mass, Is that still the case?
    Still the case, though guitar building has mostly overtaken mandolin building around here lately, so that's different.

  22. #44
    Registered User j. condino's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    When I do use an adjustable truss rod, I make my own out of titanium for the lower weight and the different flexing response vs steel.
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  24. #45
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    Default Re: Neck reinforcement vs a truss rod

    Titanium metal has a density of ~4.5 g/cm3; the density of iron is ~7.8. So that'll save about 43% compared to the mass of a steel truss rod. So a Ti rod would be in the neighborhood of 17 g. Subtract about 5 g for the wood removed from the neck for the channel for the truss rod, and that's a net gain of 12 g for the total mass of the neck (not counting the adjusting nut and a washer. Not bad, but lighter tuners would help a lot more. A set of mandolin tuners made from TI instead of steel could be made to have a mass in the neighborhood of 90 grams (not counting grommets). A set of tuners like that in combination with a mostly hollow CF shell neck would get me a lot closer to what I'd like.

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    Default Re: Neck reinforcement vs a truss rod

    Sounds like a business opportunity for someone.
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  26. #47
    Adrian Minarovic
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    Default Re: Neck reinforcement vs a truss rod

    Loar trussrods were 0.152" diameter which is thinner compared to modern that are mostly 3/16".
    I'm using metric 4 mm rod that is close to original and I believe the weight of it is closer to 20 g.
    The weigth at the end of the headstock is much more important and using tuners that are no unnecessarily heavy helps much more than replacing rod with titanium. Even thick ebony veneer on the headstock makes more feelable difference as it is almost twice as heavy as lighter maple or birch veneer. I've also seen mandolins with really thick fingerboards (1/4" or so) and very thick necks which makes the instrument neck-heavy even without trussrod.
    Many folks who played my instruments notice at first how light they are (compared to what they own) and that the balance is very good and I don't underbuild my instruments by any means.
    Adrian

  27. #48

    Default Re: Neck reinforcement vs a truss rod

    I suspect the acolytes of the F Gibsons and related things, with their scrolls and truss rods, and almost mandatory shoulder straps, have no idea how nice a light mandolin feels.
    Save overhanging mass? Plain headstock, tuners without fancy embossing, and therefore heavy plates - and those likely never-used truss rods. What I really don’t get, though, is solid-body electric guitars that weigh much more than my sledgehammer.

  28. #49
    coprolite mandroid's Avatar
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    Question Re: Neck reinforcement vs a truss rod

    Wasn't there a hardwood [oak] piece inside the mahogany neck on pre truss rod Gibsons?
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  29. #50
    Registered User sunburst's Avatar
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    Default Re: Neck reinforcement vs a truss rod

    Quote Originally Posted by mandroid View Post
    Wasn't there a hardwood [oak] piece inside the mahogany neck on pre truss rod Gibsons?
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