Unneeded Neck Shim?

Discussion in 'Hardware, Setup & Repair [BG]' started by minginitis, Apr 27, 2020.


  1. Good morning/afternoon everyone. I’m writing because I seem to be having an issue with one of my basses buzzing/dulling out above the 12th fret on all strings. The instrument is a Fender style bass tuned to BEAD with 50-110 strings. The specs are: Neck Relief @ the 7th fret- .012, String Height @ the 17th fret- Bass side 7/64 and 6/64 Treble side. I recently brought the bass to a luthier for a setup/fret level/dress in which he also decided to add a neck shim. My question is, is the neck shim possibly causing the buzzing/choking? The bass has a Badass 1 bridge and the saddles are jacked up pretty high. Any thoughts or suggestions would be appreciated. Thanks!
     
  2. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    The shim is not the root cause of choking above the 12th fret. The saddles are too low for the frets in that area. How are you measuring the neck relief? You should be measuring at the 7th when fretting the first fret and the 17th. And it's better to measure the string height at the 12th fret - you avoid the complications introduced if there happens to be a bit of a ski jump, but the strings certainly seem to be high enough to avoid buzz.

    A shim is used to change the neck to body angle to accomplish one of three things.
    1. Allow for more vertical adjustment of the saddles - i.e. they are bottomed out and the strings are still too high, or they are topped out and are still too low.
    2. Provide greater break angle between the bridge saddle and the anchor point of the string.
    3. Increase clearance between the string and body for such things as hooking your finger under the string for popping.

    If none of these apply to your bass the shim is totally unnecessary.

    Since your luthier levelled the frets, I have to wonder why the saddles are "jacked up pretty high" and you are still choking out on the upper frets. Without making any adjustments, measure the relief and string height as I outlined above and report back - maybe I can figure it out.
     
    RSBBass, minginitis and Lownote38 like this.
  3. Paulabass

    Paulabass

    Sep 18, 2017
    Those strings might to too light for BEAD. MOST PEOPLE USE A .125 or .130 for the B.
     
    mech and Vinny_G like this.
  4. Lownote38

    Lownote38

    Aug 8, 2013
    Nashville, TN
    I've used as light as a 118 for a B string with no problems. That shouldn't change whether frets buzz, or not, unless the neck needs an adjustment after the string gauge is changed.
     
    JCooper and minginitis like this.
  5. The neck relief measured at the 7th fret with the 1st and 17th frets fretted reads .012. The string height at the 12th fret reads 5/64s for both the bass and treble sides. The high saddles make me question whether the neck shim is even necessary. What do you think?
     
  6. The bass is a 36” scale so the 110 B string isn’t as loose as you’d think it would be.
     
  7. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Measurements look good so far. I doubt that the neck shim is necessary, unless it is a "reverse" shim i.e. on the outboard part of the neck pocket rather than the butt end.
     
    minginitis likes this.
  8. Do you think that it’s possible that the shim is creating a neck angle responsible for the fret buzz/choke? The action is already pretty high, and there aren’t any high frets. What’s your recommendation?
     
  9. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    An angled shim can absolutely choke the last few frets. Due to the angle, The last frets will be closer to the strings. Especially if it's a sharper angle.
     
    minginitis likes this.
  10. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Since the string height is good at the 12th and 17th frets, it's not the shim that's causing the problem. The idea that a shim can cause this kind of problem is a fallacy based on a misunderstanding of the geometry.
     
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  11. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    It's actually the geometry that proves that a Shim can cause the problem. The sharper the angle at the heel, the closer the higher frets will be to the strings. Too much shim angle will basically run you out of adjustment at the bridge with respect to the higher frets.

    Good at the 12th and 17th frets is a relative term. The question is is the 17th fret closer to the strings or the same as the 12th fret.
    There could also be a Ski-jump situation. But after paying for a fret level, there shouldn't be.

    A shim is good if you can't get your bridge saddles low enough but that is not the case here.
     
  12. The string height is 5/64th at the 12th fret and in between 5 and 6/64th at the 17th. If all the measurements are good, what do you think is causing frets 12+ to buzz/choke?
     
  13. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    If you are sure there's not a Ski-Jump or high fret than it's a matter of raising the action. If you have run out of adjustment at the saddles then you need to reduce the amount of shim or change the angle.

    If you paid someone to do all this work for you, I feel you should take it back and address the Choking/buzzing.
     
  14. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    That's a typical symptom of a ski jump. But you say that you had a luthier do a fret level, so I would assume he dealt with the ski jump if there was one - if he didn't then the frets are not level. One last check - what is the string height at the last fret?
     
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  15. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    This is so misleading. If you change the neck angle and maintain the same string height (measured between the fret and the string -say at the 12th fret) the heel will not be closer to the strings. It's like saying if you change your strings they will be out of tune - only true if you don't tune up. If you add a shim without adjusting the bridge you will have a problem.

    I am not criticizing what you are saying - I think you understand the geometry. But for someone who hasn't fully grasped the layout it may seem that the shim is the culprit when it's not.
     
    Last edited: Apr 28, 2020
    minginitis and 202dy like this.
  16. Here are all the measurements taken again this morning. String height at the 12th is 6/64ths, 17th is 6/64ths, and 24th is 5/64ths.
     
  17. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    There's a lot more than meets the eye geometrically. Where does the center of the relief fall with regards to the neck pocket?
    I will agree with your evaluation if we are talking about a completely flat neck but once you add relief into the equation it all changes.
    The thing is that you have to be able to press down on the strings at any given fret and still "clear" the remaining frets from the "lowest" area of relief. This is where the angle of the shim starts to have a varying effect.
     
  18. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    OK I have a picture now. There is less clearance at the 24th fret than at the 17th and 12th. That clearly indicates a ski jump condition.

    Your luthier did not level the frets end to end. If you paid for a complete fret levelling as opposed to a spot levelling, you need to take the instrument back to the luthier and ask him to do what you paid for. Since there is a ski jump it is not level end to end.
     
    FunkHead likes this.
  19. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    No. This is a misunderstanding of the geometry. The shim introduced an angle to the neck, but if the string height was raised to the same clearance at the 12th fret the shim will have no effect on string clearances further up. It is clear from the OP’s last post that the clearance at the 12th is adequate but it is less at the 17th. The shim isn’t doing that - there’s a bend in the neck.
     
  20. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    You're probably right. I must just be missing something in my logic.
     
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