Gold leafed Hardtail Stratocaster. Fixing a nut which is cut slightly too low

I’ve been playing-in this hardtail Stratocaster, for a few weeks now. I’m reasonably pleased with it in general – but I’m looking to find fault, and I’ve noticed there’s a slight fret buzz on the higher strings when I play “enthusiastically”. Because the buzz occurs only on the strings when they’re played open, and not anywhere beyond the first fret – this isn’t something that can be simply fixed by adjusting the saddles at the bridge, and raising the string height. The problem lies where the strings emerge from the nut and have to clear the first fret. When the strings are sounded open, they vibrate between fixed points at the nut and at the bridge. The neck is usually adjusted so there’s a slight bow, and this provides room for the displacement each string achieves during it’s vibration, (maximum at the 12th fret). Because this troublesome buzz happens only on a couple of open strings – it’s apparent that the clearance at the points where the affected strings pass over the first fret, is slightly too small. As the string vibrates and the note rings out, the strings come into slight contact with the top of the first fret. The contact isn’t enough to completely “choke” the note, but it causes the notes to “ring” a little, and there’s a slight harshness or “buzz” to the tone, which just isn’t there when fretted notes are played further up the neck.

Shaped and slotted bone nut. I don’t really want to do all that re-shaping again, from scratch

This is one of those minor faults which really bugs, and it’s also one of the problems of using general, standard specifications for setting up a guitar. The fact is – what can work for some instruments just doesn’t necessarily always work for all others. Especially if the setup has used some dimensions from a reference guitar with a very low action, as is the case here.

The geometry at the nut is complicated, critical, and so easy to get wrong. Slight differences in neck action, fret height, and nut height can all result in the vibrating open strings coming into partial contact with the first fret. This produces the annoying “bloom”, “buzz” or slight ringing tone, as the note continues to sound out. Getting the correct height and clearance is essential, because not only does it affect the feel and ease of playing in open positions, (for example: those often difficult barre chord positions at the first fret) – it also directly affects the intonation of the strings and the critical inter-string tuning relationships.

The ideal setup should have the strings passing just over the first fret when they are fretted at the third. (The indicating string length therefore runs from second fret, over first, to the nut). Because the ideal clearance is so small – it’s difficult to measure, and equally difficult to fashion accurately – especially given the small incremental difference between success and failure. The dimension can be quantified, checked and measured with feeler gauges – but it can also be decided by a simple matter of “feel”. Unfortunately – that introduces a certain amount of “trial and error” – and that’s just not really practical when it’s possible to completely ruin a nut by over cutting a single slot by just a couple of thousandths of an inch. Normally – a simple calculation can be done which adds the measured first fret height to a standard, approximated, ideal “fit factor”. That’s pretty much how nuts are cut at the factory. The allowance is always on the conservative side – since it’s easy to reduce the string height at the nut, but impossible to raise. That might explain why many guitars are a “little stiff” when fresh out of the box, and why they play much better having been set up properly.

Of course – finding that perfect “fit factor”, without doing all the trial and error yourself, is tricky, and time consuming. There’s a lot of opinion out there, in books and on the web, and from what I can deduce, Fender guitars seem to like to be set up with nut slots cut to a dimension which reflects the measured first fret height plus a 0.020″ tolerance on the bass side – 0.018″ on the treble. I’ve previously followed some of Phil Taylor’s recommended settings for Dave Gilmour’s Black Strat, and they set the clearances much lower – however, it just goes to show that all of the setup settings have to work together. You can’t always pick and choose, and what works on one instrument won’t necessarily work on all. I probably should have started out with a more standard set of dimensions, and then refined from there, as required. As it happens – I’ve cut the treble side slightly low. That’s resulting in the intermittent low-fret buzz when playing.

Tapping out the nut

It’s a real bummer to blow a nut by just a few thousandths of an inch. Having accurately sized, fitted and shaped the bone to fit the slot and slope away properly – the slots have been carefully cut, shaped and flared, and now I find two of them needed just a couple fewer strokes of the nut slotting file. That’s a lot of work to throw away, just for the sake of a small, annoying mistake. But if the nut isn’t doing it’s job properly – that’s all anyone can do. You can’t exactly glue the powdered bone back into place – can you?

Well – actually – Dan Erlewine at StewMac will tell you that it is possible – by building up thin layers of cyanoacrylate on the bottom of the low string slots, with baking powder sprinkled on top to set the glue off, and build into the matrix as it cures. I’ve tried it before, and it does work really well – but I’ve since come across a slightly less obvious fix which will leave my existing nut slotting and shaping clean and intact. This fix relies on raising the whole nut – by adding an extremely thin shim underneath.

So I de-tune the guitar once more, bunch and tape off the existing strings so they don’t get tangled, and then tap out the nut with a hammer and drift. This nut fits so well – I really don’t want to have to go all the way back to square one with it. (Plus – I don’t actually have any spare nuts in the toolbox, at the moment, anyway).

Fashioning a shim with a known thickness

I originally cut the treble side nut slots so they were 0.012″ above the first fret height of 0.045″. (It always really helps to keep notes for each setup, and that’s one of the reasons I keep this blog, in the first place). I really probably should have cut them in at 0.018″ above. That’s a 0.006″ error for two, perhaps three strings. It hardly seems significant – but it’s enough to ruin the setup in this case. If I can find a way to raise the entire nut by 0.006″ – then that will raise the treble side slots to the required height, and also raise the bass side to 0.070″. From there, I can cut the bass side slots down a little more – to restore their previous settings. All I have to do, is provide a 0.006″ shim. The difficulty is finding a way to fashion such a thing, to an accurate shape and dimension.

Fortunately – Dan Erlewine at StewMac has the answer again. The ideal shim material needs to be suitable so that it can be permanently fixed onto the bottom of the existing nut with cyanoacrylate glue. Cured super glue has a good, crystalline, structure which bonds well with the bone nut material, and it should help maintain a good transfer of resonance. The ideal shim needs to have a similar structure, or at least one which will bond with the glue and the bone to form a reasonably consistent whole. The ideal shim also needs to be a precise, known thickness – ideally one which I can measure and use without further preparation or modification to get it where I want it. Dan Erlewine suggests those old, surplus, guitar string envelopes. You know – the ones which you throw away after every re-stringing. The ones which are made out of that nice thin, papery, sort of vellum-like material. (The one’s you just don’t get with D’Addario strings any more). I just happen to have a few, really old, Ernie Ball envelopes hanging around the workshop. (They don’t make ’em like they used to). My digital calipers tell me that they’re made out of a consistent 0.008″ stock. The material is a sort of “hard” paper, with a non-absorbent face, very much like vellum. That will do nicely.

Shim glued to base of nut – ready for trimming

A small piece of the “vellum” is cut off one envelope, and set aside whilst the nut itself is set, upside down, on the work bench. Because the top of the nut is sloped, and because I want the nut to be fully supported, so that it’s easier to apply the glue – I sit the nut, with the bottom uppermost, using a piece of double sided tape, Blu-tack or Plasticene to keep it securely in place, and upright. I can then use a fine whip-tip applicator to apply a thin bead of liquid cyanoacrylate down the entire centre length, of the base of the nut. The oversized piece of “vellum” is then pressed down on top. The glue is pressed out towards the sides, covers the entire curved bottom of the nut, and bonds with the “vellum” almost immediately. The join is good within seconds.

Trimming off the excess shim material

Once the glue has cured – all of the excess shim material, and any excess dried glue which has oozed out, can be trimmed off using a sharp blade. The bone nut can be used to run the blade against – so it’s possible to pare the new material down around the base of the nut, so that the join is virtually undetectable. This is important, so that the ideal fit at the nut slot is maintained. Once the trimming is complete – the nut is now 0.008″ higher, but with a hard vellum base permanently bonded to the bone nut. The ever-so-slightly taller nut can then be pressed back into place, in the nut slot.

Re-slotting the nut

The shimmed nut is then re-slotted to reflect the required clearances. This is done with a StewMac “SafeSlot” clamp – by working each slot with an appropriately-sized slotting file, and with a sized metal gauge to protect from over-cutting. The bass side slots need filing down approximately the full shim thickness of 0.008″ – back to where they were before, at 0.065″ above the fingerboard. The treble side strings were the ones which needed lifting slightly, and the slots on the treble side therefore only require reducing by approximately 0.002″ to get them bang on target,at 0.063″. It’s barely a stroke for each, from the slotting files. The slots are all polished out with fine grit paper, and then a spot of silicone nut lubricant is dropped into each.

The completed, shimmed nut

The guitar is re-strung once again, and brought to tune. The treble slots have only been lifted a touch – but the effect is noticeable. There’s now no ring or buzz on any of the open strings. The open intonation and cross-string tuning relationships appear to be unaltered. Open chords sound in tune, and there’s no real detectable effect on the overall resonant feel of the notes produced. (I like to assess all of this with the guitar played acoustically, and without amplification). Looks like job done.

There are still, perhaps, a couple of things to look at – and I’ll continue to asses the setup as I play the guitar in. The treble side slots are still a little too deep, so the nut should, ideally be shaved down a little more on top, at that side – so that each of the strings sit just a string diameter down. The break angles for the high “E” and adjacent “B” strings, at the nut, are also quite shallow. No string tree has been fitted, as yet. Having the strings sit in shallower slots might require a bit more of a steeper break angle over the nut. This will help the strings stay in place and might also, further, improve the overall tone produced. Steeper break angles usually result in a more definite contact point at the end of the vibrating string. The less “meat” there is around that contact point – the less chance there is of the string moving around in there, and buzzing against the sides. This is, in itself, an occasional cause of troublesome “blooming” with sounded open strings. Another possible cause of problems, which can result from a poorly cut nut.

Lesson learned. Start cautious and conservative. Play the guitar in, and adjust the settings from there, to suit. You can take bone away from a nut – however, you can’t put it back. Start high, and adjust down from there. You can’t necessarily “dial-in” settings from another instrument – “just like that”. It’s better to introduce a playable standard, and then fine tune and refine down to the required level of finesse, for the particular instrument in hand. Take it easy. Don’t blow it…

…(but if you do – check out Dan Erlewine’s tips on YouTube. It’s not the first time he’s saved my day).

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