Neck shimming - advanced Question.

RockStarNick · #1 10-26-2009, 09:55 AM

Hey guys. Quick question about neck shimming.

I understand the overall premise of shimming a neck:

If your saddles are adjusted as LOW as they can go, and your action is still too high, shimming the neck (by inserting something towards the rear of the neck pocket) will raise the string angle relative to the body. Then you can more useful travel from your saddle height adjustment screws.

That I get.

I also understand that there's the occasional problem of a "neck hump" in some bolt on necks. I.E., the neck has proper curvature and relief from the nut to the 14th fret, but when it hits the body, there is zero relief, because the bolts are right underneath.

Especially in Fender basses, this seems to be a problem in getting the action super low. (I'm having the problem right now on my Jazz bass. And everything else is setup properly - relief, frets leveled with a radium block, and carefully crowned, action adjusted properly). No buzzing from 1-12. But above that, it buzzes.

What I would like to know is, does shimming, in any way, help with "neck hump" problems? Does it create more even relief along the entire length of the neck?

Is there any secret shimming "mojo" that happens BESIDES the relative string to body height?

My bolt-kit Carvin bass (which has a neck that joins the body at a higher fret than the Jazz) can get MUCH much lower action. I'm starting to wonder if this is because there is a more even relief-bow along the ENTIRE fretboard on the Carvin?

dmusic148 · #2 10-26-2009, 09:57 AM

Quote:

Originally Posted by RockStarNick

What I would like to know is, does shimming, in any way, help with "neck hump" problems? Does it create more even relief along the entire length of the neck?

Is there any secret shimming "mojo" that happens BESIDES the relative string to body height?

No, no, and no. You need fretwork, sorry.

202dy · #3 10-26-2009, 10:16 AM

Shimming changes the geometry of the instrument. It won't do anything else. Once the shim is inserted a set up is performed to adapt the setting to the new geometry.

Relief, string heights and radius, and intonation are adjusted in the normal way.

Meatrus · #4 10-26-2009, 10:31 AM

Could there possibly be too much relief on the Jazz? It sounds likely to me.

JLS · #5 10-26-2009, 10:36 AM

Quote:

Originally Posted by dmusic148

No, no, and no. You need fretwork, sorry.

+1

JonathanD · #6 10-26-2009, 10:39 AM

Yep, Level, Crown and Polish.

mongo2 · #7 10-26-2009, 10:54 AM

Quote:

Originally Posted by RockStarNick

Especially in Fender basses, this seems to be a problem in getting the action super low. (I'm having the problem right now on my Jazz bass. And everything else is setup properly - relief, frets leveled with a radium block, and carefully crowned, action adjusted properly). No buzzing from 1-12. But above that, it buzzes.

I may have found the problem.

RockStarNick · #8 10-26-2009, 11:22 AM

I can't believe StewMac sold me a radium block!

haha.

Sorry for the bad spelling.

After reading all the responses, I think that taking out some releif, and raising the saddles a hair, might just get the job done.

The frets are pretty much as good as it gets: level (checked with a fret rocker), sanded with a radiused block, and crowned.

I think relief is the ticket here.

I guess I was just making sure that there wasn't any other "magic" involved in shimming that I didn't understand.

Thanks guys!!!

dystopiate · #9 10-26-2009, 11:27 AM

Saw a youtube vid with Roger Sadowsky where he said that when leveling frets he creates a slight downward slope as the neck goes towards the body so he can get lower action without buzz. Seemed logical to me as long as it's slight enough to avoid intonation issues.

ubrnostrum · #10 10-26-2009, 12:20 PM

It is fairly common for bolt-on instruments to develop what's called a "tongue-lift." Essentially what this is where the end of the fingerboard pitches up and makes the frets in the upper register higher than the frets "below" it. Shimming will make this worse by emphasizing the lift (you can actually counteract the tongue lift by "reverse shimming" the neck meaning that you shim the front of the neck pocket rather than the back-- this works in a pinch, but is an ugly and an ill-advised repair, more of a bandaid). There are three solutions to this sort of problem.

#1: Live with it. Play with higher action.

#2: A level, crown, and Polish in the upper register to lower the relative heights of the frets in this area of the neck.
- depending on how bad the tongue lift is, this could end up being an extreme procedure.

#3: You need a refret and while the frets are out, the fingerboard in the upper register needs to be taken down then refretted.

I hope this helps.