Nut question

[Cary Fagan]

Hi all. The answer seems obvious to me but before I do anything...

I'm trying to lower the action on a mandolin. I'm getting buzzing on the first and second frets. It seems obvious to me that the nut is too low. I don't see any other problems in the neck.

Am I right?

[Phil Goodson]

If it buzzes on the 2nd fret when you press the 1st fret, then it still leaves a mystery. (Nut is removed from the process.)

[Cary Fagan]

Good question, Phil. Actually the buzzing is just first fret so I can't try that. If I lower the action a little closer to where I want it I can't slip a piece of paper (regular 20 lb) between the string and the first fret on the e string (the buzziest). And I can but it touches the string on the G string. But I can slip the paper under both on my well set-up, low action Passernig.

[Phil Goodson]

Yep. You may have the answer!

[colorado_al]

Sounds like you're on the right track.
I'd shim under the nut and test it out. If that fixes the issue, you can just leave the shim and be done. Or you can remove the shim, fill the nut slots and re-cut it. Or cut a new nut.

[Cary Fagan]

Thanks to both.

[rockies]

Yes, if it buzzes with the strings unfretted the nut slots are too low. Loosen strings, tape them off to the side, remove the nut and put a piece of that paper under the nut cut to nut shape) and set the nut back in place. That will raise the slots by about .007" or so. Tune up. If that works make a better shim out of some plastic sheet to be more permanent.
Good luck. Dave

[darylcrisp]

if I want the absolute lowest buzz free action, I straighten the neck(truss rod adjustment), check all the frets for level(level and dress as needed), then I cut the nut slots. sounds like a lot to do, but its not really, and it will give you a low buzz free action.

I usually find one or more ever so slightly high frets that would inhibit the lowest buzz free action.

[O. Apitius]

Hi Cary.
To check if the nut slots are too low, fret the string just ahead of the second fret then check the gap between the top of the first fret and the bottom of the string. There should be the tiniest of gaps there. Any more and the slot is higher than need be. If the string is touching, the slot is likely too low. I say likely because sometimes you can get away with a light contact but that's if you are getting no buzzing. Otherwise, it's likely too low. Of course this assumes a neck with good relief and very level frets.

[Wrnchbndr]

Unless there is a reason not to, I find it easiest to just elevate the entire nut and recut the existing slots. I pop off the nut, surround the perimeter with masking tape creating a tub shape on the underside, use multiple thin applications of CA with a CA accelerator and reshape the bottom as needed to achieve a permanent sort of shim. Its very important to keep the applications of CA as thin as you can or you end up with wet bubbles of CA -- it depends on the CA and the accelerator you use on how quickly you can do this but I've never had a problem with this method. It retains most of fitting of the nut and its easy to reform the bottom of the nut using 220 grit sandpaper on a flat surface. Once you get a solid base, you can spot apply the CA as needed and sand it back with 600. As long as the original nut is made from a quality material and you approve of the original string spacing, it saves all of the hassle of making a totally new nut from scratch.

If the nut for some reason is a difficult or dangerous/complicated removal issue, I use a good quality file to cut a 90 degree vee deeper than the offending slots and use CA to install a donor piece of matching bone, corian, or tusq into the old nut. I just reshape the donor part to conform to the overall nut and recut new slots.

[Cary Fagan]

Hi all (and a warm hi to you Oliver, it's been quite a while):
Well I put a shim under the nut (slightly too high) and it just shifted the problem down a fret. And after much thinking and some measuring (straight rule over the frets) I decided that it might need a truss rod adjustment instead, loosening the rod to allow a bit more bow. So I took out the shim and did the adjustment and yes, it seems the problem is solved and the action is low as I like it. I just did it so will let the thing settle to make sure all is right. One confusing complication seems to be one high fret (11th fret, G string) which is causing buzz just on that string on one fret. Nothing to do with the original buzzing at the first fret.

This was, I think, my first truss rod adjustment and some posts here on the cafe were a big help.

I hope this is the end of the problem, will check tomorrow and if all else is ok will deal with the one fret buzz left. Nice to get that action right.
Thanks all.

[Cary Fagan]

I meant to mention that I hadn't seen Oliver's mention of 'good neck relief' but it appears he had it there.

[EdHanrahan]

Suggestion: Look up Stewart-MacDonald's "fret rocker", designed for identifying high or low frets - they have a video. Then pull out your favorite, or least favorite, credit card and use that up & down the neck.
https://www.stewmac.com/Luthier_Tool...SABEgKw4_D_BwE

And don't be too surprised if the results near the G-string end of the fret differ from results near the E.