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Neck shim or sand heel?

Discussion in 'Hardware, Setup & Repair [BG]' started by awilkie84, Jun 22, 2014.


  1. I have a bass that seems to have come with a slope in the heel of the neck, from the factory. A friend of mine levelled all the frets but could only take the last few so far before they were too low to go further.

    I took a pair of calipers to the neck & noticed that around the 21st fret the heel is 1.5mm thinner than at the 24th fret, despite the pocket being the same depth all along.

    I don't have the money to have the frets pulled, board sanded down & refretted. What would be the better way to go about fixing this?

    Should I sand the bottom of the heel down so it's an equal thickness, or should I do what I've done temporarily & shim the back of the heel up the 1.5mm needed to equal them out?
     
  2. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    neither one will help; the problem is the profile of the fret tops, messing around with the bottom of the neck won't change that.
     
  3. If that was the case, the shim I put in on the back of the neck wouldn't have solved the problem. I just need to know if it's an acceptable modification, or if it's going to cause more harm.

    By raising the back of the heel & leaving the offending part of the heel at stock height, it changes the string pass angle over the offending area when fretting near it.
     
  4. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    all you did was raise the action, the same as if you had just adjusted the saddles higher.
     
  5. My action & saddles are quite low. Lower, in fact, than the action needed when the neck is in the pocket by itself. What I've done is changed the pivot angle of the neck in the pocket.
     
  6. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    ...which had the effect of raising the action enough to get the strings to clear the "ramp" at the end of the neck, exactly as if you left the neck where it was and raised the saddles.

    think about it a bit.
     
    IGotGas likes this.
  7. faulknersj

    faulknersj Supporting Member

    Apr 4, 2008
    Scottsdale Az
    I would try correcting it with a shim. I have put shims in the neck pockets of several of my basses to adjust the angle slightly with excellent results.

    I should add that I also tweaked the truss rod in order to get a really straight neck profile on these basses.
     
  8. I'm not explaining this correctly, obviously. The action is LOW...as in a couple of millimetres LOW.
    I'll take some pictures tomorrow. -_-
     
  9. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    shims do not change the actual profile of the fretboard, they just get the strings further or closer to it depending on any angle change.

    if adding a shim made my strings 1/32" further away at the 17th fret, it would be no different than raising the saddles until the strings were 1/32" further away at the 17th fret.

    people get oddly confused by this, but it's basic geometry.
     
    elBandito and IGotGas like this.
  10. mongo2

    mongo2

    Feb 17, 2008
    Da Shaw
    Awilkie84, a shim at the headstock end of the neck pocket has worked for me in several situations like yours. In fact, it allowed the saddles to be lowered.
     
    Last edited: Jun 23, 2014
    temmrich and awilkie84 like this.
  11. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Seems a difficult bit of geometry for quite a few people. Next to it is the geometry of the nut. Some folks just don't get it.
     
    Zooberwerx likes this.
  12. And that's where you're wrong, because a shim lowers the action at any point before the shim (in the case of a headstock end heel shim). Raising the saddles without the shim just gives you a stupidly high action across the board.
    It's simple geometry. ;) A shim like the one I've put in changes the rougly triangular shape of the neck/bridge/string dimensions into more of a parallelogram. There is now another angle in the neck pocket that didn't exist before.
     
    faulknersj likes this.
  13. 202dy

    202dy Supporting Member

    Sep 26, 2006
    And then the saddles are adjusted to the height you choose. That is the geometry of the modern guitar.

    Walter and Turnaround are correct in their teaching.
     
    Last edited: Jun 23, 2014
    Zooberwerx likes this.
  14. elBandito

    elBandito

    Dec 3, 2008
    Rotten Apple
    If you had a ski jumped neck, a shim would not really do much for it, because the truss rod has no effect on that area. You're just tilting the neck. With a ski jumped neck, what matters is the straightness of the neck from nut to heel. Bridge height can be ignored. Even when it's shimmed, the heel end will still have an up-bow, relative to the nut.

    It's like drawing a curve on a piece of paper, then rotating the piece of paper. The curve will still be there, unless you redraw or fix the curve itself on the paper.


     
    bluesdogblues likes this.
  15. Ric5

    Ric5 Supporting Member Commercial User

    Jan 29, 2008
    Colorado
    I grow organic carrots and they are not for sale
    SHIM
     
  16. mongo2

    mongo2

    Feb 17, 2008
    Da Shaw
    I've put several ski-jumped necks back into service with shimming maybe a change to lower tension strings and setup. Some are too far gone for that to work but it never hurts to try it.
     
  17. If your curve on paper is pinned at the point of the the hump and you had a reference point for the bridge, you could potentially rotate it in such a way that the hump was no longer impeding the travel of a straight line from the point of the nut over the point of the hump. Furthermore, you could then reduce the curve with the truss rod to compensate for the increased clearance, and lower the reference point of the bridge.
     
  18. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    There seems to be some confusion about a ski jump. It's a rise in the fingerboard over the area where the neck meets the body of the instrument. This area is not affected by the truss rod which only works on the area from the body joint to the nut, the black area.

    In the illustration below, the black line represents the neck from the nut to the body joint. The red line indicates the area of the ski jump - greatly exaggerated in the illustration for clarity. The brown section is the body of the instrument, the blue triangle represents the saddles on the bridge, and the green line is a string.

    In the first case the neck is lying parallel to the body. In the second illustration the neck is tilted up by 3 degrees - both the black and red areas. This is the same effect as putting a shim in the pocket, furthest from the bridge. You can see that the bridge saddles can be lowered substantially to give the same amount of clearance over the end of the fingerboard but the string clearance over the entire board remains the same as in the first illustration. All that has changed is the height of the bridge saddles and the angle of the neck to the body.

    If you were to tighten the truss rod, you would introduce a back bow in the black part of the neck. It would do nothing to correct the ski jump. In fact it would likely add additional problems of string clearance at the lower (nut-side) frets.

    Neither the truss rod nor a shim will have any effect on the ski jump. SkiJump.

    SkiJumBackBow.

    Above I added an illustration of what would happen if you added a shim and tightened the truss rod. You can see the problems that would be introduced from the first fret to the middle of the neck.
     
    Last edited: Jun 23, 2014
    walterw likes this.
  19. Ok...so explain why my adding a shim fixed my issue? If I take the shim out, my ramp comes back, if I put the shim in, issue solved again.

    Here's my experience on what my shim is doing. You've put a pivot point where the ramp is moving into the body when the rest of the neck goes up. This isn't possible when you shim.
    PQr1WBa.

    Note that the pivot point I create is anchored at the ramp. The ramp doesn't move up or down.
     
  20. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    In your second illustration, there is a bend in the neck where it meets the body. You seem to suggest that tightening the truss rod will straighten that bend. It will not. It will simply put a back bow in the area between the body joint and the nut, with the maximum hump of that bow occurring halfway between the body joint and the nut. There is nothing you can do with the truss rod to take the kink at the body out. See my third illustration.
     

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