To Shim or Not

[Mary Pat]

I had my MM set up by a luthier. #It is not yet a year old. # He put in a bone nut and lowered the action. I had Martin Bluegrass strings on it. #It played really nice. # He suggested that I experiment with different strings and that the new nut should work fine with a heavier string. #So eventually I put on a little heavier string and have had problems ever since. # There is a “twang” or harsh sound from one of the “A” strings. #Then my husband raised the bridge and the “A” was fine but the unwanted sound was now on one the “D” strings. #I changed to TI lights and still the same problem. #The “twang” sound is not present when it is fretted on the first fret and is most evident on the upstroke of either picking or chording. #Would a .003 or .004 shim stock inserted under the bone nut be advisable? # Or any other ideas?? This is such an annoying problem. #Thanks.

[sunburst]

You really need a new nut if this one is too low. You can put a shim under it and it may sound just as good to you, but that doesn't really FIX the problem, it just remedies it.
I'm going to look in Frets.com and see if Frank has a section on building up a nut with superglue..... be right back.

OK I'm back. I didn't find a section on this in frets.com, but you can get a tiny drop of superglue on a toothpick and dab it into a low nut slot. Obviously, you want to do this with no strings on the mandolin and take whatever precautions necessary to insure that no glue gets on the mandolin anywhere else. After the superglue is thoroughly dry, you can recut the string slot and you have basically shimed that one slot from the top rather than from underneath. The shim being the glue in the slot. This quickie repair can last a suprisingly long time.

[Chris Baird]

You should put a little baking soda into the slot before you put the CA glue in. It will make the glue set up instantly and much harder.

[Michael Lewis]

Mary Pat, I agree with your idea of putting a shim under the nut. As long as it fits well and is secure it should be fine. This will cause other strings to rise somewhat, and they should lowered a bit to keep things even.

From your description I can't tell if the strings are lightly buzzing on the first fret or that the string notches are slightly goobered. Look at the string clearance at the first fret when that string is fretted at the 3rd or 4th fret. If there is clearance then the nut slot needs attention.

[Michael H Geimer]

I had a shim placed under the nut of my Bitterroot so I could lower the hieght5 of the bridge, take most of all of the relief out of the neck, and have a nice consistent action all the way up the fret board. I couldn't be happier with the result.

- Benignus

[Mary Pat]

From your description I can't tell if the strings are lightly buzzing on the first fret or that the string notches are slightly goobered. #Look at the string clearance at the first fret when that string is fretted at the 3rd or 4th fret. #If there is clearance then the nut slot needs attention.

Thanks everyone for the suggestions.

Michael I did your test and find the only string that has clearance is the "G". I'm confused. Does that mean to shim the bridge or to file the nut slots? If I need to shim what thickness do you recommend and would metal be acceptable? Thanks again for all of your help. Mary Pat

[mandofiddle]

Personally, I'd take it back to the luthier and request that he redo the job. Doesn't sound like he did it right the first time...

[samuel]

I agree with Mando... take it back and have him fix it. Did it sound alright when you left there?

[Mary Pat]

Yes Samual it sounded great when I left there but that was in the fall. The trouble started when I began to experiment with different strings. I wonder if I was so excited about the lower action and easier playablity that I didn't notice the unwanted sound. It seems like it's a little late to complain at this point.

[keithd]

Hi Mary,

A couple of thoughts occur to me here. I had this happen with a recently purchased vintage mandolin that had been set up with very low action by a great luthier. Later, I put on lighter strings than the set up was configured for, and the lower tensioned, lighter strings move around a lot more than the heavier, tighter strings, resulting in quit a lot of buzz. When I switched back to the heavier strings, things were fine again. But it sounds like you went from lightish strings to heavier, so it must be something else. One possibility is the bridge placement. If you placed the bridge even a fraction farther from the nut than the original set up, then that might have lowered the action a bit more and be causing the strings to buzz. You might check again by putting a set of the original strings back on and double checking the bridge location.

Regarding the super glue solution for raising the nut at one string slot, I had a luthier roommate once who used to do this by sanding some bone dust and mixing it with the super glue first. If the nut is just not working for you and you've made up your mind to go back to your luthier, then you might give this a try; he can correct things if it doesn't work out. Be sure though to file the slot with the proper type of nut file (like they sell at StewMac) to give the correct profile and size to the slot.

I second going back to your luthier with it though, and asking (nicely) for help. There's nothing worse than having that buzzing, especially after it was set up so good before. It could just be the change of season and humidity or something.

Best of luck with this,

Keith

[crawdad]

If the symptoms occur just when changing strings, chances are very good that this is just a neck adjustment that is needed. Heavier strings pull the neck up more because they have more tension. I bet the luthier did the set up based on the string guage you were using. The sound you are hearing on the A string is from the string rattling on the first fret. This is because there is too little relief in the neck when you switch to light strings. They have less "pull" or tension than the heavier strings you had.

There are really only three things that can cause action and setup to change. First--the weather. Wood changes with relative humidity and temperature. Second, changing string guages to either lighter or heavier than what was used when the instrument was set up. Third, and less likely, the truss rod is not holding its tension--but that is much less frequent.

Decide what guage and type of strings you really want, go back to the luthier and explain whats happening. A little tweak of the neck and your problems will be solved. Don't start messing with the nut. Its very possible that the nut is not the problem. You got a real fine hot rod setup probably, but it requires the same guage of strings you started with. Once you start changing things, the action and setup will change too.

[HHansen]

As a luthier, my advise would be to abstain from attemping any repair unless you understand exactly what the problem is. A twangy sound on an open string can be from a slot that is too deep, or a string that is not properly seated in the bottom of the slot, or a backbowed neck, or a loose first fret, or even something else entirely. If you're not sure which, you may end up doing something you oughtn't. I would give your luthier the chance to fix the problem, which he most likely can. If that doesn't work out, find a better luthier. Good luck!

[Michael Lewis]

Mary Pat, if you can get the nut out easily you can shim it by placing a piece of business card cut to size under it. This should elevate the nut and get the strings off the first fret. This is a temporary fix that should work for a while. If the nut doesn't come out easily take your mandolin to a luthier.

[Mary Pat]

Thank you all again for taking the time to help me with this problem. Lots of wisdom generously shared.

Respectfully,
Mary Pat