Is It Possible to "Fill In" a Nut Slot to Start Over? UPDATE: Shaping the Nut Slot...

[Pete Andreev]

To make a long story short, I'm installing a new bone nut and I took a little too long trying to get the nut slot nice and flat. I couldn't get both sides of the nut to lay nicely in the slot and ended up filing too much. Now the nut slot is too deep...and still not flat.

It wouldn't be as much of a problem if I was using a nut blank but I got a pre-shaped Gibson nut from StewMac.

Is there a way for me to somehow fill in the nut slot so that I can start over??

UPDATE

The CA glue + baking soda worked like a charm...really, really great tip. Now I just need to make sure I don't file it too deep again, but I'm having trouble.

Any tips for squaring the nut slot up and getting it perfectly flat? I'm filing with a mill file and checking the fit very often...but I just can't get the ends of the nut to fit perfectly in the slot.

[Jon Hiltbrand]

CA and dust, baking soda, etc can be used for filling string slots, but I would NOT recommend using any kind of superglue and dust fill under the nut.

When you say you would rather the shelf be straight than angled, which one was it to begin with??  That sort of thing should be chosen when designing a guitar, not when replacing a nut.  Removing a slight bit of wood to true up a shelf that has been damaged is okay, but removing much wood at all here is very scary! Radically changing the shape of the shelf is not a good idea. 

Shape the nut fit the shelf not the other way around.

[John]

My bad, I assumed we were talking about nut string slots. What Jon said.

[Mike Kolb]

Here's a thought about nut slots, and maybe one reason why they don't end-up as perfect as we'd like to see them.  One of the techniques I've wrestled-with over the years has been trying to keep a file square and flat when truing-up the slot.

It's far too easy (especially in an area as short as a nut shelf) to ever-so-slightly tilt the file toward one end or the other, resulting in a very slight arc that's high in the middle... leaving the ends to show space under the nut. Then it becomes a game of "shortening the table legs to even them out".   I think just recognizing that is half the battle.

This hasn't been very well thought-out on my part (particularly the neck-holding portion) but here's a germ of an idea for helping this situation... with a big tip to Frank Ford's fret-tang nipper for the initial idea of a file rolling on adjustable bearings.  

Maybe I'll work on building one someday, maybe not, but I think the basic idea of keeping a file dead-true along the nut shelf will work wonders for this issue.

[Paul Verticchio]

VERY interesting concept, Mike.  Run with it :)

kudos :)

[Mike Kolb]

Thanks, Paul.... but, at my age, it's more like I'll SHUFFLE with it :)

[Paul Verticchio]

LMAO, Mike.

I hear ya, brother.:)

[Andrew]

Ive found that a lot of files have a little burr shape that will cut a notch shape in the bottom of the nut shelf, which will be quite visible under the nut after it is installed, so you want to watch this. Also, standard mill files dont often fit a nut slot very well.

I usually use a sharp chisel or micro chisel to clean out any glue thats messing with my fit, then test fit a nut that has been squared up. If the slots just a little out of square then Ill shave a little off the bottom where necessary to get a nice fit. If its giving me a hard time for some reason and its just a small amount of wood to remove, ive found that some psa 320 paper on the bottom of the nut can work nicely to get the fit very close. You just have to make sure to trim the sandpaper very cleanly to get clean corners in the slot, and your nut has to be thicknessed to fit the slot just right. I used to use needle files a lot to clean and true nut slots, but 90 percent of the time I do it with a well sharpened and lapped chisel. That way the tool tells you where a high spot is without removing any more wood than that.

If a slot is really whacked and removing material is risky, I just put a concave radius on the bottom of the nut so the visible ends look good (or acceptable at least, with some guitars...)

As for shaping the ends, I put the snug fitting nut in the slot and trace the neck to headstock transition shape on the bottom and front of the nut with a very sharp pencil (I like 6H or 8H Staedtler pencils for this stuff), I then shape JUST through this lines with assorted needle files, or sandpaper on a dowel, or the end of my belt sander - basically whatever I can find that gets me the shape I need. I find you dont often have a nut slot that calls for nice straight/square ends.

My best suggestion would be to order several nut blanks next time. For what they cost, sometimes its better to start over than to fight with something thats boogered, just like a fret or whatnot.

[Paul Verticchio]

Pete,

Although the CA & dust worked for you in this instance, it's not an 'admired or approved' fix in this situation. I, for one, discourage that solution. But, what is done is done.

If I need to raise the nut shelf bed, I glue a matching strip of whatever the neck wood is into the shelf slot. You can then fill any gaps after the nut is installed.

And again, installing and adjusting a nut is not an intuitive skill. It takes a LOT practice and experience.  When dealing with nuts and saddles, it's ALWAYS a good idea to order at LEAST 2 of everything you need. Like I said, we've all experienced nut making, fitting & adjusting fiascoes. Having a spare relieves a tremendous amount of frustration when having to rework an "Oooops" repair, especially when you're dealing with an 'expendable' item.

Best of luck with your final outcome :)  Oh ya, just out of curiosity, what make & model guitar are you repairing?

[Frank Ford]

OK, here's the deal.  You may want the nut slot to be perfectly flat, but you don't need to have it that way.  

In cutting or trimming the bottom of the nut or the nut slot, I always try to make it very slightly "hollow" in the center, so that the nut fits absolutely tightly right at the ends where you can see it from the edge.  (By "very" slightly, I mean just a few thousandths of an inch - not something measured with a ruler.)

In the center section, it doesn't quite touch completely across.  Same goes for the interior corners.  I try to cut the slot with sharp corners at the bottom, but when I make the nut, I "break" the corners just a bit except for the last 1/16" at the ends.  Trying to fit a perfectly square and sharp corner into a perfectly square and sharp corner for the full length is a procedure for CNC machining, and a monumental waste of time for hand work.

That way, I get a nice fit, and the nut is well supported.  Nuts get glued in place along the end of the fingerboard, not at the bottom.

As to tooling for trimming the bottom of the slot, a narrow chisel works best for me.

And, before you ask, NO I DO NOT THINK THE NUT NEEDS TO FIT SOLIDLY ON THE BOTTOM FOR ANY TONAL REASON.

[John]

I hollow the feet of archtop and mandolin bridges before fitting them for the same reason. 

[Glen H]

I learn something new every day, and I don't mind one bit setting conventional wisdom aside!

Thanks Frank

[Andrew]

Great advice, especially the part about relieving the bottom edges.

The only thing I would change is to put the part about the gluing at the top, in caps lol. I learned this one the hard way. :P