Grain orientation in neck?

Discussion in 'Luthier's Corner' started by Tim Barber, Mar 2, 2004.

  1. Tim Barber

    Tim Barber Commercial User

    Apr 28, 2003
    Serenity Valley
    Owner: Barber Music
    OK folks, say you have a neck where the wood is not exactly quarter-sawn. Obviously individual pieces of wood will vary but, all other things being equal, is there any inherent advantage to making a 2-piece neck with the grain arranged symmetrically, as opposed to a 1-piece? It obviously doesn't change the strength, but I'm thinking of resistance to uneven warping. Has anyone A/B tested this?

    cheap graphic:

    One piece
    / / / / / / / / / / / / / / / /
    / / / / / / / / / / / / / / / /
    / / / / / / / / / / / / / / / /

    two piece
    \ \ \ \ \ \ \ \/ / / / / / / /
    \ \ \ \ \ \ \ \/ / / / / / / /
    \ \ \ \ \ \ \ \/ / / / / / / /

    well, you get the idea.
  2. Woodboy


    Jun 9, 2003
    St. Louis, MO
    If you have uneven warping the piece isn't well seasoned or was poorly kiln dried. My personal bias is towards a one piece neck, or a one piece neck shaft and a grafted head.
  3. I've never done it myself but the little materials engineer in my head says the second way is better. I say this because if the orientation of the grain is going to affect the way the wood reacts to changes in humidity and whatnot, having it orientated such will counteract whatever happens in the horizontal plane. Equal and opposite forces in the one plane and whatnot.

    However I squashed the little materials engineer and told him to shut up and am now studying chemical engineering with a biotech minor, so yeah...

    Josh D
  4. adolganov


    Jan 15, 2004
    Just some common sense.

    The fist picture is 2 pieces for your neck just after separation. Red arrows depict the potential warpage direction (it is, obviously, the same for the two).


    To change the direction of the grain as you want it, you chould turn one of the pieces (for examle, right one) :


    But look at the red arrows: nothing changed!

    Think of the right-threaded rods or bolts: one cannot make it left-threaded just by changing his position :)
  5. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Owner: FBB Bass Works
    These arrows seem to indicate the wood twisting. Is this what you intended? What about the many other ways a board may warp: cupping, kinking, bowing, crooking, et cetera?

    For some of these other ways in which wood may move, the two piece neck may help keep the neck straight. The trick is forecasting the movement of the wood and orienting the boards so that when they do move, they will move against each other.
  6. Suburban


    Jan 15, 2001
    lower mid Sweden
    Another thing that those pictures makes clear, is that once glued together, the room for movement is diminished.

    What actually happens is that the glue makes the second piece stop twisting because the first pieces twist moves the glue in the other direction!
    Have a look at the arrows and think hard, you'll follow me.

    The same goes for any kind of warp: many thin laminates are more stable.
  7. pkr2


    Apr 28, 2000
    coastal N.C.

    I'm sorry but even with the pix ,I don't get your point.
  8. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    Not exactly right, Sub.

    What you're forgetting is that this same relationship (the bond that causes the translational aspect of movement due to twist of one half to oppose that of the other half) exists in any two "virtual halves" of a board that hasn't been split- so splitting it and regluing it offers no advantage that isn't there in the unsplit board.

    The reglued board is better in twist than either of the two halves would be alone, but not better than the original board.
  9. Suburban


    Jan 15, 2001
    lower mid Sweden
    Well, Peter Pilot, haven't we done this before? :smug:

    What we didn't mention at that time is cross-linking. the glue actually works as a crosslinking. Which is what we do to polyethene (the softest of all soft polymeres) to make it into PEX - the best material this far for waterpipes. NB: "pipes" not "hoses" because the PEX is hard and stiff similar to brass tubes.

    When we glue two pices of wood together, we enter a crosslink into the composite. This thin layer will indeed counteract any deformation, beacuse the movement between fibers in the wood is hindered.

    Then again, due to the macroscopic scale of our laminates, the impact will not be very great - but present!
    If we go for thinner laminates, like Kubicki and Curbow use, we are in a very different league.
    If we go for even thinner laminates, somebody will propose the term "composite" instead of "wooden" neck...whatever teh difference may be, semantically (wood is a natural composite).
  10. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    Yes indeed! ;)
    But my point here is that the two halves (before splitting) were already crosslinked, and the the movement between fibers was already hindered.
  11. Suburban


    Jan 15, 2001
    lower mid Sweden
    And my point is that is further hindered!:D

    Exactly how much depends on how far it is between these extra crosslinks.

    'nuff knitpicking from my part. See you in another issue, Peter :D
  12. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001