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Modern Single Cut design and Relief Control

Discussion in 'Luthier's Corner' started by SteveCS, Mar 4, 2017.

  1. SteveCS


    Nov 19, 2014
    Hampshire, UK
    This question is really a follow-up from a thread discussing the advantages or otherwise of the modern single-cut design, where the upper body extends almost half way down the neck.

    I posed the question how might such a design affect the ability of the truss rod to evenly control relief along the entire fingerboard length when there is a radical change in stiffness where the upper bout starts. And if the truss rod cannot control things, what alternative controls, if any, have been developed? Or is the top section so stiff that it is immune to normal climatic and string tension changes and can simply be 'baked in' by the builder but is therefore not adjustable by the player?
  2. Beej


    Feb 10, 2007
    Victoria, BC
    I have two designs which can be either single or double cut - the single cut version on both has the upper bout meeting the neck continuously until about the 11th fret. On both, I've found no difference at all in how the truss rod adjusts the neck compared to their double cut cousins.

    These are both 34" designs, so that leaves 17" or so of neck to have relief adjusted freely, and that has been more than enough to address any setup challenges. I wouldn't call the change in stiffness where the upper bout starts as "radical". I don't have numbers, but I would not imagine that the differences in stiffness to be enormously different as compared to a double cut "open" neck design. The stiffness in the build of the neck in my case is pretty significant anyway, especially with a hard fingerboard and CF stiffening rods the way I build (although probably going to aluminum stiffeners now based on an excellent discussion in this very forum).

    A well built neck should not really need a lot of "control" by trussrod adjustments for relief and should be relatively stable, with the capacity for adjustments for player style and temp/humidity changes as necessary. I think that your original notion is perhaps informed by an assumption that a single cut variation on the design exerts a greater influence on the stiffness of the neck/body join and concurrent adjustability than it actually does in my own experience.

    Thanks for bringing this up, very interesting topic. I'm looking forward to hearing thoughts from other builders who have built both single and doublecut variations of their designs... :D
    SteveCS likes this.
  3. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, on a standard neck, when you loosen the truss rod, almost all of the relief curvature happens between the nut and the 12th fret. Most of the curvature is between the 2nd and the 8th. It's supposed to be that way, with the curve flattening out down through the heel.

    So, typical single-cut design construction, joining the upper body to the neck out to the 10th or 12th, doesn't have any real effect on the relief or the operation of the truss rod. It does pretty much eliminate any 12th fret kink (ski jump) problems, and it will increase the overall stiffness of the neck. Singlecut basses will usually have more brightness and clarity than doublecuts, if all else is equal.
    BassHappy, Beej and SteveCS like this.
  4. SteveCS


    Nov 19, 2014
    Hampshire, UK
    Thanks for the informative, enlightening and polite replies chaps. :)
    Beej likes this.
  5. HaMMerHeD


    May 20, 2005
    Norman, OK, USA
    My single cut design has the nut-most neck screw attaching at about the 15th fret, though the strap button is approximately parallel with the 12th. I have not noticed any difficulty in getting the neck adjusted correctly.
  6. Gopherbassist


    Jan 19, 2008
    I'd like to read about this, do you have a link or remember the thread title?

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