Last of the nut stuff for now. I thought I’d follow up the last few weeks worth of information on shimming nuts and filling slots with something a little more involved and — truth be told — a little less common.
Grafting fresh bone into a worn or ruined nut slot.
Recapping on things, we generally choose to shim under a nut or fill a problem slot when we have some reason not to replace the nut (which is generally the more ideal solution). Sometimes, this is a monetary concern or sometimes we just want a quick fix. And, sometimes, we’re faced with a guitar with some vintage mojo or value and we just don’t want to install a new nut.
This last circumstance is probably when you’ll employ a bone graft.
We can even fix a slot that’s THIS screwed up.
Nut repair with a bone graft
Filling slots and shimming nuts is all well and good. But if the slot is really messed up, these methods might not do the trick. For badly cut slots that are really deep or — more likely — are cut really wide so that the string can slide about from side to side, we might restort to a bone graft.
It’s possible to glue in a new piece of bone to fill the problem area.
Check it out…
First widen the problem nut slot to accept the bone graft.
First off, we need to clean up the slot and make it into a regular shape. Doing so means it’s easier to shape our new bone graft so it fits. So, use a file to widen and even out the problem slot. A needle file will probably work for this — even a square one would give nice even slot walls — but I’ve used a larger (bass-nut size) nut file here.
Use some scrap/donor bone and shape to fit your widened slot.
It’s easier to fit your ‘graft’ to the slot than the other way around so, when you have a nice even slot, begin shaping a bone off-cut to shape. Use some 220 grit sandpaper on a flat surface and get the with right so the graft fits snugly in the slot. Not too snugly, by the way — it’s easy to split the nut if you have to force things.
When the width is good, work on getting the bottom shaped for a good fit. As I mentioned, I like using a rounded bottom here which means a bit more work in fitting the graft but I prefer the end result.
Trim the excess, leaving your graft piece a little larger than the edges of the nut.
When the graft is fitting well, use a pencil to roughly mark the area to be inserted and cut off some of the excess. At this point, don’t worry about getting these cuts so they’re flush with the nut. Well tidy that up later. For now, just hack off most of the unwanted bone and leave enough to easily handle.
I use the medium viscosity superglue for this job (that is, the ‘regular’ stuff you’ll buy pretty much anywhere). Splodge out a little blob onto a piece of plastic and use a toothpick or bent-over guitar string to ‘paint’ the inside of your slot walls. I’m pretty liberal with the glue at this point (but be very careful if you’ve been brave enough to do this with the nut still on the guitar).
Quickly pop your graft into the slot and, if necessary, hold it in place. A little superglue accelerator is fine on this job.
Glue the graft piece into the nut.
Once dry, you can use files, sandpapers, and polishing compound to clean up your grafted-in bone so it matches the original as much as possible.
Then you just need to cut a new slot and you’re in business.
Bring the grafted piece flush all around and you’re ready to cut a new slot.
As I said, this is a bit more involved and likely not something that many readers will have to do. The requirement for ‘scrap’ bone pieces probably pushes this towards the more professional end of the DIY spectrum but, if you have the parts and tools, it’s a relatively straightforward job and well within the realm of most. You may never have to use it but maybe it’ll be one of those things that gets filed away at the back of your brain where it’ll surface in forty years to save the day. 😉
One last consideration. Obviously, this solution is aimed at bone nuts. Many plastic and synthetic nuts don’t respond so well to superglue and you may not get a good bond that will hold over time. If we’re talking about retaining vintage vibe, we’re probably not talking about plastic nuts, though, so it’s likely fine. There won’t usually be the same pressures to avoid replacing a synthetic nut.
We’ve considered nuts where the slots had worn (or been cut) too low. This causes buzzing when the string is played in the open position. We’ve looked at fixing this problem but shimming under the nut — with a hardwood shim and with a rock-hard superglue-impregnated cardboard shim — to raise it up.
And, if you don’t want a new nut, or aren’t in a position to get one right now, these are both good alternatives.
But there’s another way.
Fill a low guitar or bass nut slot with baking soda and superglue
Baking soda and superglue nut repair
The TL;DR description is that you fill the problem nut slot with baking soda and squidge in some superglue.
For a decent result, do the following:
Clean the slot with some sandpaper before you attempt a fill
First off clean out the slot. Use some folded over sandpaper (it doesn’t matter at this point if you widen or lower the slot because you’re fixing that later). You ideally want to clean out any gunk, lubricant, pencil graphite, etc. The sandpaper will also roughen the side of the slot slightly which will help at later stages. For this reason, go with around 220 or 320 grit paper.
Fine white powder used by musicians. Relax, it’s baking soda.
The first of the magic ingredients is baking soda. The bakers among you might be wondering if you can substitute baking powder. The answer is I’ve no idea but it’ll probably be just fine. I’ve read about the ‘baking soda and superglue’ trick for years but I don’t think it matters what you use. For instance, when I do this, I usually use bone dust I’ve collected from sanding other nuts and saddles. That works great, so I reckon that any fine, white powder substance you can find in the backstage area will likely do the trick.
Pack the offending slot well with baking soda.
Pack the offending nut slot with baking soda. And I do mean pack - press it in firmly. If I’m doing this, I’ll generally back fill completely and re-cut the slot. That’s probably not necessary if you just need to raise the slot a little to quickly stop a buzz. Fill up as much as you need with baking soda. Try to keep the front edge of your fill flush with the front edge of the nut.
Splodge out a little low-viscosity superglue onto a non-porus (and disposable) surface
Time for the second magic ingredient. Get some low-viscosity superglue (I’d strongly recommend not using the thicker stuff for this job) and squirt out a little onto something disposable and non-porous. As you can see, the inside of plastic/foil string packs works splendidly. In a little puddle like this, the superglue won’t dry for ages.
Use a toothpick to drop a little superglue where you want it
Use something like a toothpick (the end of a string folded over double works well too) to pick up a drop of superglue. Touch it to the baking powder and it should instantly wick into it. If you’re doing this while the nut is on your guitar, I’d recommend masking off around the nut and keeping a sheet of kitchen towel handy in case of any misplaced drips.
Wait a while for the superglue to cure and you can tidy up your repaired nut slot.
Now wait. Seriously. Wait a while. Give it a half hour if you can. Let it cure all through before you work on it or try string up. Personally, I don’t like to use accelerator on this — I prefer to let it cure and dry on its own without being shocked into curing from the outside in.
If you’ve got a deep or wide slot to fill, I recommend doing it in stages. Repeat the packing and glueing steps a few times. Doing so will help ensure good superglue penetration. Too deep and the glue can begin to harden before it wicks its way right to the bottom.
Two caveats on the backing soda and superglue nut fill repair
I’d consider it temporary. I don’t do this repair often but when I do, I add a disclaimer. It can prevent having to replace an ‘original’ nut but it might not be permanent. It can certainly get you out of trouble when you discover your open string’s buzzing during soundcheck, but I’d advise following up with a more ‘certain’ repair when time allows.
As with all of the shimming and filling nut repairs, ideally, the slots should be filed down and ‘set up’ properly afterwards. Otherwise you might be swapping slots that are too low for ones that are too high. It’s the lesser of two evils but it’s even better to get it sorted properly when you can.
Next time, I’ve a final nut fix for you. In the meantime, if you’re a touring musician or tech who decides to cross international borders with a small bag of baking powder, you should keep this email to help your defence.
Remember, last time, when I talked about shimming a nut with hardwood? Remember how I mentioned that sometimes you might see a nut shimmed with a piece of cardboard and I advised against that?
Well, there’s an exception.
Thanks to Richard for emailing to remind me of this exception. I knew about it but have never actually done it so it’s good to get a ‘this works’ recommendation. I tried it and, can confirm that it’s a good way to go.
Using paper or cardboard as a shim material CAN work.
For all intents and purposes, the process is the same as last time. Instead of a piece of wood, we glue a piece of cardboard to the bottom of the nut.
“Oh, but cardboard’s soft. What about my tone?” you yell.
“Ahhh. Calm down about your precious tone. There’s a trick,” I say.
I’ll get to it in a minute. First let’s recap the procedure…
How to shim a nut with cardboard
First off, you don’t want any shiny surfaces for your glueing operation. Use some sandpaper (around 220 or 320 grit or so) to lightly scuff the bottom of the nut. Then, if your cardboard shim has a glossy/satin coating, very lightly scuff that with the sandpaper. Just go in one direction to avoid wrinkling or creasing the cardboard (like some idiot did before taking this photo). Remember that this is a very light sanding just to remove the glossy film. A couple of gently rubs will do the trick.
if your paper or card has a gloss coating, remove it
Then, apply a uniform layer of superglue to the bottom of your nut. Doesn’t need to be too thick but a little squeeze-out later isn’t the end of the world.
Coat the bottom of the nut with superglue.
Place the nut on your cardboard (on a flat surface) and apply pressure. Wait for it to cure off. The glue drying to the cardboard will be pretty fast but any blobby squeeze-out might be a little slower (some accelerator is handy if you have it — otherwise wait a couple of minutes).
Stick the nut to the card/paper
Use an exacto knife to trim the cardboard close to the edges. Don’t worry about getting in tight to the nut edge. We’ll sort that out later. Just don't tear out chunks inside the nut's perimeter.
Trim the paper close to the nut edges. Be careful not to tear it.
Now the trick.
The low-viscosity, water-thin stuff is best for this job. What you want to do is to soak the bottom of the cardboard with superglue. Hold the nut with a pliers or tweezers as you do this. The low-viscosity glue can run and dribble easily, and it sticks to fingers amazingly quickly. Ideally, though, you’ll be careful and not have any drips. Keep watching as you go and use a piece of paper towel if you see a drip.
Saturate the paper with low-viscosity superglue
Sorry for the out-of-focus thing on that image — not always easy to do this stuff one-handed.
The idea is to completely impregnate the cardboard with superglue (which is why the thin stuff is better). Once you think it’s soaked in, wait for it to dry completely.
When dry, use some sandpaper on a flat surface to sand back the protruding cardboard/glue until it’s flush with the sides of the nut. You can use the sandpaper to even up the bottom of the glue-hardened cardboard too
The result is usually relatively discreet. And, because the cardboard is now completely soaked in superglue, it’s become super hard and it’s not going to have a major impact on your tone.
Sand the edges of your glue-hardened paper shim. It’s super hard now.
There it is. Glue-hardened cardboard shims. Cool.
Personally, I prefer the idea of a hunk of wood but this is, absolutely, a sound fix and will work perfectly well. It’ll certainly get you out of a hole if you find yourself with a low nut.
A couple of times, I’ve talked about shimming a neck (the right way) to alter the angle the neck attaches to the guitar body. This is sometimes done on guitars to lower the action when the bridge saddles are bottomed out and have no more downward travel. Shimming is also used to get, sort of, the opposite effect — make it possible to raise the saddles (to give more string break angle over them) while keeping the action comfortable.
And it’s this latter that I want to touch on a little more. I’ve felt like I may not have explained it as well as I could. I’ll rectify that, but first, we need to consider neck angles in a little more depth.
Why does a guitar neck angle back?
What is a guitar neck angle for?
Right. Let’s go back to the old days. The days before djent and rock ‘n’ roll. Back then, you might have had a fancy, new-fangled flat-top acoustic or you might have had an arch-top guitar.
The arch-top guitar has a construction similar to older instruments like the violin. The strings are anchored in the tuners, at one end, and in a tailpiece at the other. Sitting on top of an arched top, with the strings passing over it, is the bridge.
The bridge’s job is to transfer the string vibration to the top so that it can vibrate. The vibrating top, vibrates the air in the body and that squirts out the sound hole(s) as sound.
Archtop neck angle
If the angle the strings pass over this bridge is a bit too shallow, there’s not as much pressure pressing downwards. Less pressure means less efficient transfer of string vibration (a lot of energy is lost to sting floppiness) and that’s bad for tone.
So, to keep a decently steep angle over it, the bridge is made quite tall. When the bridge is tall, the neck has to be angled backwards to allow a comfortable action. Imagine the ridiculous situation below…
What an archtop would look like with no neck angle
In this way, the instrument’s construction dictated it needed a tall bridge, which dictated it needed a backwards-angled neck.
Fast-forward a few years and you’ve got solid body instruments with pickups and crazy sci-fi-sounding names. Now we have a clean slate. These pickup things mean we don’t need to have so much downward pressure to get an olde-time arched top vibrating. What are we going to do?
Well, Gibson, decided to go down the solid instrument that looks like an arch-top route. The Les Paul had an arched top on a solid hunk of lumber. Cool. Their tun-o-matic bridge wasn’t archtop-tall but it was relatively tall and this meant the Les Paul retained a backwards neck angle.
Les Paul neck angle illustration
Down at Fender, on the other hand, Leo decided he’d pick an easier route. You see, fashioning a neck joint for an angled neck is a pain in the… erm… neck. Leo was all about easy construction techniques and angled necks weren’t something he wanted to mess with.
So, he went and designed a shorter bridge and screwed his neck into a flat-bottomed pocket in the body. No nasty angles. Pretty obvious, really.
A Strat (and most Fenders) has no neck angle.
And here’s where we come back to the neck-shimming.
Even though these solid-body guitars don’t require a vibrating top to produce their sound, it turns out that the angle strings break over the saddle is still important. Floppy strings bring their own problems on a solid-body instrument.
This wasn't so much of an issue with something like a Tele or a Strat because the strings passed through the body (or anchored) right behind the saddles, automatically giving a steep angle. And it wasn’t a problem on a Gibson with the strings anchored in a tailpiece quite close to the bridge. All seemed well for a while.
Then Leo went and made a Jazzmaster. Enamoured with the whole ‘jazz’ vibe, he designed a cool vibrato tailpiece and he located it down the end of the body — like on an arch-top.
Of course, moving the string anchor point all the way back there made for a much more shallow string angle over the bridge. The shallow angle made for less downward pressure on the bridge. Less pressure made for floppier strings that wouldn't stay put, rattly bridge saddles and screws, and the issues Jazzmaster players have wrestled with for years.
Similar to the arch-top solution, having a taller bridge would help enormously but that means the action gets higher and it’s hard to play.
Unless you’ve got a neck angle.
Jazzmaster comparison - standard and shimmed neck. Check out the string angle over the bridge.
Shimming the neck artificially creates our neck angle and means we can raise the bridge up without screwing with our action.
So, we’ve sort of brought Leo Fender full-circle and back to the archtop guitars — complete with tailpieces and neck angles — that his first designs had completely eschewed.
Gerry’s Last Word on Shimming
Remember to do it properly.
You must use full pocket, wedge-shaped shims. If you missed this stuff the first time (or second, or subsequent times), it’s important you don’t just shove a bit of card or something under the end of your neck. Doing that can cost you hassle and money. Check out Neck Shimming Made Easy and the other links for more info.