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Thread: Carbon Fiber Straight D tube?

  1. #1

    Default Carbon Fiber Straight D tube?

    Hi all,

    I'm new here. I'm building an F5 and was thinking about using a CF truss rod. I came across this and think it looks promising. Was wondering if anyone here has used one and what your thoughts are.

    https://dragonplate.com/Carbon-Fiber...be-5-x-45-x-16

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  2. #2
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    Default Re: Carbon Fiber Straight D tube?

    A solid carbon fiber bar will be stronger and cost considerably less.

    To me, the hollow tube looks like an expensive gimmick.
    I don't understand the thinking of the designer. Do they intend for a metal adjusting rod to be used inside the tube?
    And if you were to put a metal adjusting rod inside and tighten it later, I would think that it might crack or shatter the CF tube[???].

    If you use CF for a neck reinforcement, I recommend that you recess it 1/16" below the neck surface and cover it with a maple strip. That's because its nearly impossible to sand, scrape, or file CF level to the neck surface. It is tough stuff.
    Last edited by rcc56; Dec-15-2019 at 7:47pm.

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  4. #3

    Default Re: Carbon Fiber Straight D tube?

    The principle is that the material along the neutral axis (area of the neck which is neither in tension nor compression) does nothing to add stiffness to a structure. So a hollow tube can often be similar in stiffness while being much less mass. Air is one of the best engineering materials - Two 1/2" steel bars spaced apart from the neutral axis can be orders of magnitude stiffer than the same amount of metal stuck together right next to the neutral axis.

    That being said, on a mandolin, the neck is so small and so short that the benefits of this kind of structure are negligible, I just use two 3mm x 10mm pultruded carbon fiber rods for mandolins.

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  6. #4
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    Default Re: Carbon Fiber Straight D tube?

    Well, I don't want to distract from the topic, neither do I wish to be argumentative, but I still don't understand.

    We've got 150 - 200 lbs. of constant string tension on the neck, with moments of torque at the head and body joint. I don't understand how any significant portion of the neck that might be considered neutral.

    Anyway, I would save 50 bucks and go with a solid reinforcement. Carbon fiber doesn't weigh much.
    Last edited by rcc56; Dec-15-2019 at 9:14pm.

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  8. #5

    Default Re: Carbon Fiber Straight D tube?

    rcc56, jusr think of any kind of a stick (or beam in technical words) that is being bent. The side towards the tension is in compression, and the opposite side is in tension. An horizontal tree branch is an example, where gravity is doing the bending. So, between the compression side (the string side on a mando), and the tension side (the underside of the neck) there has to exist a neutral plane. In that any reinforcement in this small ‘stick’ is pretty much going to wind up in the middle, it really is itself likely close to neutral, not that that makes it useless, again because it is such a thin structure. Marty’s two rods, one toward the string side and one toward the back side represents good engineering, in effect an “I” beam. Again speaking as an outsider, since mandolins are pretty sturdy without any reinforcement, and if properly made, stable over a lifetime, we’re talking about some small issues. Just be sure that any reinforcement is in solid (glue or mechanical) contact with the wood; if it’s to be useful at all.

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  10. #6

    Default Re: Carbon Fiber Straight D tube?

    Quote Originally Posted by rcc56 View Post
    Well, I don't want to distract from the topic, neither do I wish to be argumentative, but I still don't understand.

    We've got 150 - 200 lbs. of constant string tension on the neck, with moments of torque at the head and body joint. I don't understand how any significant portion of the neck that might be considered neutral.

    Anyway, I would save 50 bucks and go with a solid reinforcement. Carbon fiber doesn't weigh much.
    I'm not trying to be argumentative, either, just having a conversation. Wasn't trying to be a jerk.

    Ok - imagine a 1" diameter tube, cut in half (solid D shape), 12" long, made of solid carbon fiber.
    That weighs 1.5 pounds. Carbon fiber is very heavy, relative to wood. It's also very stiff. The only reason why we can make carbon fiber structures just as stiff, but lighter, than wood or other materials, is because there's air in the middle. So we take advantage of carbon fiber's extreme tensile strength, but design around its weaknesses, like its density, to make light structures.

    In a mandolin neck, there is a significant portion of the neck wood which is also doing little to nothing to add stiffness. It is not practicable to remove it, so we don't. And the savings in mass would be negligible relative to the risks inherent in adding a void to the neck.

    But carbon fiber is massive enough that we can't just add solid slugs of it to our necks, and have the result be desireable.

    I will reiterate that I agree - solid reinforcement is fine in mandolin necks, if added in slender strips perpendicular to the pull of the strings.

    But a hollow tube of the same mass is always stronger than the same mass in a solid block. And when it comes to carbon fiber, the hollow tube may, in fact, be cheaper to manufacture. It (and other composites) is/are a bit of an odd duck relative to conventional materials.

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  12. #7

    Default Re: Carbon Fiber Straight D tube?

    Marty, I like to ask silly questions, so here: I have relatively tiny paws, just about good enough for a mando with a thin neck, and useless on, say, a classical guitar. Have any builders engineered thin neck structures for persons so debilitated? That is, keeping normal fretboard widths but removing the underneath dimensions.

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  14. #8

    Default Re: Carbon Fiber Straight D tube?

    Thanks everyone for your comments, and the explanations of the mechanics behind the engineering principles. I know it's an expensive truss rod ($75). I'm intrigued, but will think about it. I like the idea of removing some weight out of the neck/headstock, and this CF-D would do it. Since its my first mandolin build, I'm willing to try it. It will be for me. :-).

  15. #9
    Adrian Minarovic
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    Default Re: Carbon Fiber Straight D tube?

    Quote Originally Posted by Steve Bollman View Post
    Thanks everyone for your comments, and the explanations of the mechanics behind the engineering principles. I know it's an expensive truss rod ($75). I'm intrigued, but will think about it. I like the idea of removing some weight out of the neck/headstock, and this CF-D would do it. Since its my first mandolin build, I'm willing to try it. It will be for me. :-).
    I would just skip things like these with first build. There are MUCH MUCH more important things that first-timer needs to grasp. Just follow your desired model for first few builds and when you have all the basics mastered then you can delve into such details as type of truss rod or tap tuning. Save your money for the next one.
    I had spent few years studying violin/mandolin acoustic and all the tuning theories before I attempted my first build and now I can clearly say I wasted a lot of time. It was not because the tuning is not working as such but because I as beginner just had no chance caring about such details when I had to learn all the elementary stuff. I still believe the tuning and similar metods will give us better results but only experienced makers could use it effectively. Just imagine beginner sitting in the racing car - he would crash at the first curve because he couldn't handle the basics of proper use of brakes...
    Adrian

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  17. #10

    Default Re: Carbon Fiber Straight D tube?

    Quote Originally Posted by HoGo View Post
    I would just skip things like these with first build. There are MUCH MUCH more important things that first-timer needs to grasp. Just follow your desired model for first few builds and when you have all the basics mastered then you can delve into such details as type of truss rod or tap tuning. Save your money for the next one.
    I had spent few years studying violin/mandolin acoustic and all the tuning theories before I attempted my first build and now I can clearly say I wasted a lot of time. It was not because the tuning is not working as such but because I as beginner just had no chance caring about such details when I had to learn all the elementary stuff. I still believe the tuning and similar metods will give us better results but only experienced makers could use it effectively. Just imagine beginner sitting in the racing car - he would crash at the first curve because he couldn't handle the basics of proper use of brakes...

    Thanks, Hogo. I meant this was my first mandolin build, not my first build. I have many years as a woodworker and 6 as a guitar builder. But I hear you.

  18. #11
    Registered User j. condino's Avatar
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    Default Re: Carbon Fiber Straight D tube?

    Those are made by Dragonplate / Alred.

    J.B. Alred, who owns both, is a friend of mine. As such, I've used a LOT of his product, in all kinds of dimensions. I have used the carbon fiber D tube in mandolins, the larger guitar sized model, and the gigantic one designed for double bass including the neck heel extension. They all have merits and can be very useful depending upon your engineering needs...but....

    For a mandolin, you can get a very usable equivalent working strength from the straight carbon fiber bars that they sell for an approx. $8 investment. For full time builders, that equates to hundreds of dollars (possibly thousands over a few dozen D tubes- the big bass one is around $150!) saved every year with no perceivable difference in structure.

    I'd hope that by now everyone here has figured out that Dragonplate supplies almost all of the other companies who sell carbon fiber in the US. You can buy the same 24" long section for approx. $8 direct from them that the other catalog supply houses tack on their commission & sell for approx. $20 and up, plus you can select from almost 4000 different models...

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  20. #12
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    Default Re: Carbon Fiber Straight D tube?

    Either a quarter inch diameter rod or a .375" rod from Dragonplate is less than 5 bucks. You get light and strong. A solid .25" x .375" is a little more.
    Play it like you mean it

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  21. #13

    Default Re: Carbon Fiber Straight D tube?

    As someone who often misses the obvious, please tell me what the advantage would be in using a non-adjustable CF tube or rod over a normal metal adjustable truss rod? And, why would someone pay more to do that? Other than being hi-tech for the sake of being hi-tech.

  22. #14
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    Default Re: Carbon Fiber Straight D tube?

    Stiffer, lighter, actually costs less.
    Play it like you mean it

    Not all the clams are at the beach

    Arrow G
    Clark 2 point
    Ratliff CountryBoy A
    00-21 (voiced by Eldon Stutzman)

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  24. #15

    Default Re: Carbon Fiber Straight D tube?

    Two different functions. A reinforcement makes the neck more resistant to warping over time. It is in contact at all points. A truss rod as usually described is free to move in the neck and is used to adjust the shape by applying tension between the two ends. It might be called a reinforcement but it’s really an independent part.

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  26. #16
    Adrian Minarovic
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    Default Re: Carbon Fiber Straight D tube?

    Quote Originally Posted by Steve Bollman View Post
    Thanks, Hogo. I meant this was my first mandolin build, not my first build. I have many years as a woodworker and 6 as a guitar builder. But I hear you.
    I though you are not a real noob, but there are so many luthier specific tasks in (especially archtop) mandolin building that can be real trial of skills even for seasoned woodworker. I had some experience with woodwork when I built my first mandolin and I can tell you I started understanding what and why I was really doing after 4-5 builds.
    Adrian

  27. #17
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    Default Re: Carbon Fiber Straight D tube?

    Checking around on dragonplate.com and thought I'd order three pieces of .250" x 48" carbon fiber rod to experiment with. Total for the order is $33.33. That's quite reasonable. But the shipping -- ground, to North Carolina -- is $41.46.

    Believe I'll have to take a pass. That's a shame.

  28. #18

    Default Re: Carbon Fiber Straight D tube?

    Quote Originally Posted by Jonathan Ward View Post
    Checking around on dragonplate.com and thought I'd order three pieces of .250" x 48" carbon fiber rod to experiment with. Total for the order is $33.33. That's quite reasonable. But the shipping -- ground, to North Carolina -- is $41.46.

    Believe I'll have to take a pass. That's a shame.
    Try ordering shorter lengths. 4' lengths are expensive to ship, but you don't actually need a length that long (or even half that length) for any instrument.

  29. #19
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    Default Re: Carbon Fiber Straight D tube?

    Good suggestion, Marty. Challenge accepted and answered. Six 24" pieces will cost $36.66, but the shipping drops to $21.96. Which is more acceptable, but still seems a but harsh for shipping light little pieces. But I placed the order .

  30. #20
    Registered User j. condino's Avatar
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    Default Re: Carbon Fiber Straight D tube?

    The same order from Stew Mac would be almost $150.

    How can you still be complaining about this??????

    Consider it free shipping with an adjusted price and be thankful you are still up almost $90. A company that deals with $100k+ orders from the aerospace industry just allowed you to nitpick through an immense catalog with zero minimum order and gave you the best price in the nation............

  31. #21
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    Default Re: Carbon Fiber Straight D tube?

    Okay, James, good point. I am satisfied with my purchase and will not complain again.

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  33. #22

    Default Re: Carbon Fiber Straight D tube?

    Not to dis carbon fiber, but I've built 5 mandos with regular truss rods and don't consider the weight in the neck to be significant. Even with medium gauge strings they require very little, if any torquing. My concern would be that if down the road a player decides they want a little relief in the neck, the only recourse would be to file it out of the frets.

  34. #23
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    Default Re: Carbon Fiber Straight D tube?

    Just to follow up on this thread, I want to give a shout out to the Dragonplate/Allred folks. They are super-efficient and prompt on order processing and shipping, and also do a great job of communicating during the process. I thanked them for their excellent service and got a nice personal note back from a manager. That's how you create customers for life.

  35. #24

    Default Re: Carbon Fiber Straight D tube?

    Hi- I built a mandocello with a Dtube 3 years ago with a 25 1/2 in scale. It sounds great and the neck has stayed perfectly straight without a truss rod. I am currently finishing up an f5 with the same. You actually get enough material with the purchase to build 2 necks. I'll be another month finishing details but I can let you know how I feel about the result if you aren't in a hurry. This is number 9 so I think I have a fair amount of experience to compare.
    Joe Hendrick

  36. #25

    Default Re: Carbon Fiber Straight D tube?

    I forgot to include a link to youtube that I posted when I was installing the Dtube on the Mandocello. I just epoxy them in with less than 1/16 of recess and float epoxy over the carbon fiber. I score up the epoxy for grip before gluing with hide glue.

    https://www.youtube.com/watch?v=rb_vZ-SglW8&t=401s
    Joe Hendrick

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