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Neck curvature?

Discussion in 'Luthier's Corner' started by freatles, Jan 20, 2014.

  1. freatles

    freatles

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    Ok let's kick off with the curve that peeves most people most: neck relief.

    While drawing plans, do you count on a simple curve from 0 fret to last fret?

    Or maybe a curve and straight part?

    As I am drawing a composite bass without a truss rod, there is only one chance to get this right!
  2. Means2nEnd

    Means2nEnd Supporting Member

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    My Modulus is older without the truss rod and when strings are off it is laser straight but when tension is on with strings is provides the perfect relief just a hair... FWIW
  3. 4to5to6

    4to5to6 Bassist Supporting Member

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    Relief neck curve follows the envelope of the vibrating string. Usually there is less curve with lower action as you can't dig in as much and must use a lighter touch. Usually there is a very small drop off on the last 4 or 5 frets.

    Fretless basses are the toughest to get right as the relief influences the tone. I found that I must use an 18" long block to dress the frets.
  4. Smilodon

    Smilodon Supporting Member

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    Why would you make it without a truss rod, though?

    Couldn't you integrate something into the mold? Maybe use CF instead of steel to keep the weight down?


    (I'm not trying to criticize. I'm just curious. :) )
  5. MPU

    MPU

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    I just took a cf bass back/neck out of mold. It's very, very stiff to bend even without cf under fretboard and fretboard but still I'm not going to make the bass without truss rod. Weightwise there will be maybe 100-200g more with rod but I just want to be able to adjust the neck in case it's needed.
  6. pfox14

    pfox14

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    Why are you going to the trouble of building a bass and not installing a truss rod? Big risk IMO.
  7. freatles

    freatles

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    I think I will use 3 mm (~1/8") curve that ends on the 12th fret. Whacha think?


    Why no truss rod? There should not be need for one.

    Carbon composite neck is going to be stiffer than stiff - that stuff will not bend. A truss rod wouldn't help as far as I know. Gonna put that 200g extra in the structure rather than truss rod.

    Means2nEnd - thats very valuable comment to me, thank you sir!

    4to5to6 - thanks for pointing that out. Yes it's going to be fretless, too.

    Smilodon - because it should not need a truss rod. Carbon fiber composite should be immune to heat expansion and moisture.

    MPU - moi vaan! As far as I can see, you are going to either break the neck or the truss rod when adjusting. I bet a corner of the rod will tear through the composite. Again, CFC doesn't bend or flex. I maybe wrong here, or perhaps I am thinking of different type of composite structure that you are going to use.
  8. MPU

    MPU

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    It will flex just enough when it's made thin enough to flex a bit. Truss rod is in for slight adjustment, not for bowing the neck. At least Status and Zon has truss rods in their cf necks. You can make the neck stiff enough not to bend for sure.
  9. freatles

    freatles

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    Also, there's the neck rotation! I think 11 degrees.

    What about the neck cross section, then?

    My idea is to have a flat neck that is very thin (like a cellphone!) ~10mm / 2/5" with rounded corners. So, its like a rounded rectangle.

    Also, want to make one that has a triangle cross section (rounded corners of course).
  10. Smilodon

    Smilodon Supporting Member

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    CF can actually be very flexible. It all depend on how it's constructed. (They even make reed valves and archery bows from CF)

    There is this general assumption that CF composites are very stiff, light and strong. In reality the material by it self isn't all that spectacular unless the structure is made to take advantage of the properties of CF.

    How is the construction going to be? If you are going for a 10mm solid neck it will probably not bend much, but it will also be fairly heavy. A thinner walled, thicker neck with a foam core or maybe a hollow neck will probably make more sense.

    As for the truss rod, you could probably get away with not using one but you would need to make the neck with the correct stiffness. Too stiff and you get no relief, too flexible and you get too much relief. With a truss rod you will be able to adjust the relief a bit. (you are then using the TR as an adjustment mechanism and not as a means to counteract string tension.) CF will be more than strong enough to hold the tension of the TR if the design is reinforced in the correct places.
  11. freatles

    freatles

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    Also, there's the fretboard radius to consider that I forgot to mention in my previous post.

    Smilodon - I'm going for a monocoque (hollow) structure. At the moment I have it drawn as a kind of "E-profile" (two cell) resisting the bending and twisting forces.

    - Up to four times more material resisting string pull, versus the top, for example.

    I am not going to construct it, a shop will do that for me. Aiming for < 400 grams weight (thats under 1 lb). And I wouldn't mind if there was no change in relief due to string tension.
  12. MPU

    MPU

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    IMO very thin neck is not so nice as a bit thicker neck. If you think what's the most relaxed grip for your hand it's not something where you have your thumb almost touching your fingers.
    I made one twisted neck. Very comfortable to play but quite a challenge to make right, especially if no adjustment of relief can be done.
  13. freatles

    freatles

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    Well, having a thin neck *is* something of an experiment, as I've never seen one! I hope I hope to get to it in a week or five.

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