Repairing a Broken Guitar Neck (The Stronger Way)

So you've somehow managed to break your guitar head clean off the neck. With this in mind, it's probably a Gibson/Epiphone design with the extremely slanted head and you probably dropped it. You can glue and clamp it up good as new, maybe paint the bit that broke to match. That's fine.

The problems start when you have a relatively clean vertical break rather than a horizontal one, leaving you sod-all area to paste your glue of choice. Or maybe it did break horizontally and you just want a stronger repair. Either way, that's where this Instructable comes in.

You will need:
One broken guitar. Or more, you clumsy goose.
Some manner of picky thing. Like a metal toothpick.
PVA glue or equivalent. You might like Gorilla or hide; just don't use epoxies, they're too brittle.
A router. The kind that's pronounced 'raut', not 'root'. It makes routs. Gouges in wood. Does nothing for your internet connection.
Some wood of the same kind as your neck. Rule of thumb: Mahogany for Gibson, Meranti or Sapele for Epiphone, Maple for Fender.
Some kind of straight-cutting saw. I like my bandsaw.
Some kind of shaping tool. Rasps, files and sandpaper in my case.

Additional funthings:
A modeller's paintbrush
Wood filler
Fine wet & dry paper
An airbrush
Matching paint

Step 1: Gluing and Clamping

This is the easiest step right here. Clean up all of your exposed surfaces with your weird metal pick thing. Get all the little bits of broken wood out of there that are going to interfere with the two halves fitting back together like a particularly good jigsaw.

Next, you take your head and neck, and cover the surfaces with your wood glue. I found a little modeller's paint brush really useful for this step, it gets you right in all them little cracks and crevices. 

Next comes the clamping. Now, everyone will tell you to use some kind of specially made jig to make sure it clamps straight, but I just used a ton of clamps until it sat properly. It's definitely worth me pointing out that I clamped it up first and checked that I could do this before I glued it up.

For a lot of you, this will be enough. Unfortunately due to the nature of my break, it's not gonna cut the mustard as-is. With the vertical break, this step serves pretty much the sole purpose of holding the two parts in place while you work on them at the same time.

Step 2: Routing the Reinforcement Channels (Pt. 1)

So on its own, this neck'll probably snap like a twig the second you try and tune it. I'm not going to test that, because I really can't be arsed to clean out all the glue and reattach it. What we really need is some wood that bridges the gap between the two pieces.

The selector switch is probably the highest part of the guitar. Take off the nut and pop it into the body to save risking snapping it.

Put something down on your work surface to preserve your precious pristine finish, clamp the guitar down and place a nice heavy block of something either side of the head/neck joint to raise your router up. Safety specs, I forgot the safety specs. Use 'em or lose 'em. And by the second 'em I mean your eyes.

The channels you rout shouldn't have corners. Round as possible. It's tempting to rout corners because it's easier to shape the wood that's going to fill it, but trust me, corners in this case are really bad; they're stress risers, meaning they concentrate the stress felt on a part at these points. If you've ever seen an aeroplane window you know what I'm talking about, don't want them popping now, do we!

Round corners good, square corners bad.

Step 3: Making the Reinforcement Blocks (Pt. 1)

First thing to do with making the reinforcement blocks is to make a template. Because of the unusual shape, the blocks can't just be whacked out with a saw, they've got to be shaped.

Grab yourself a trusty post-it, then run your nail around the edge of the rout. Cut this out with some scissors, then check it fits properly. If it doesn't, well, you have more post its.

Transfer your template onto a piece of wood (unfortunately I only had sapele, turns out the neck was meranti after all) and chop it out roughly on the bandsaw. The trick now is to shape it with a file, repeatedly checking to see if it fits. Notice a high spot, file it a little, check it again. Do this until you have a perfect snug fit.

Glue them buggers in.

Once the glue has set, you should carve them roughly to match the original neck profile. I like to use a rasp for neck profiling, you can use your teeth if you prefer.

Step 4: Routing the Reinforcement Channels (Pt. 2)

Now we have a rough neck shape, it's time to take ol' routie the router to it again! I mean, you could leave this step out, but it's even stronger still if you do this.

What we're going to do is make a shallow rout (not as deep as the truss rod) across the whole back of the neck. The same principles apply as before, no corners and all that. I just used a straight edge either end. This will not only serve to strengthen the neck further, but also to hide any potentially unsightly gaps you may have created with not quite getting your blocks perfect. So little of the original wood will remain, it really won't matter.

Once this has been routed out, you can use your chosen filler (I'm quite fond of the terracotta-coloured milliput) to fill in the small gaps. Fortunately, mine was nigh-on perfect so no filling for me.

Step 5: Making the Reinforcement Blocks (Pt. 2)

Same again, run your nail round a post-it and cut out a block to suit. This one matters a lot more in terms of fit, as it's going to be the one that's actually seen as well as a benefit to strength. It also allows you to add a volute if you want one, further increasing strength and looking pretty nice in the process.

Rasp your new block to shape. The purpose of carving in the last step seems a little clearer now, because you've got guides everywhere to help maintain the original profile. Once this is done, the whole area needs sanding, filling, and sanding smooth again. Don't worry if you sand away at the surrounding paintwork, the airbrush'll overlap anyway. It's also worth filling and sanding the face of the headstock now too, if the crack was visible.

At this point, virtually none of the original wood that broke is present. This can only be a good thing, because the original wood was clearly weakest around that area.

Step 6: Painting It Up

Fortunately, even though I used different woods, I could still do an invisible repair on this guitar on account of the finish being solid-colour. Unfortunately, it's Epiphone's Pelham Blue. This meant I couldn't find it in poly anywhere, and it's noticeably lighter than other Pelhams. Not to worry though, the good folks at Rothko and Frost gave me some good advice as to how to go about mixing up some nitro to match the colour (lightly shoot the blue over a silver base).

It's worth mentioning at this point, that if your guitar has a nitrocellulose finish you can not paint poly over it. Nitro expands and contracts throughout its life never curing as hard as poly, meaning it will crack a poly finish over the top of it.

The opposite is true for painting nitro over poly. Because polyurethane is nice and stable, you're fine with the ever-changing nitro sitting on top of it just like it would on bare wood. Fender's nitro-finished guitars are even undercoated with polyurethane because it gives a nice thick surface that can be sanded perfectly flat, filling in all the pores in the wood.

There are many Instructables out there on painting, so just as a recap:
- Apply 2 or 3 coats of primer
- Wait 24 hours and lightly wet sand using fine paper to remove any high points
- Apply plenty of thin colour coats, leaving about 15 minutes between coats to avoid runs
- Wait another 24 hours and lightly wet sand again, repeating previous step if necessary
- Apply plenty of thin top gloss layers
- Wait about a fortnight - you're not going to get it much more cured for now
- Wet sand with extremely fine paper and buff with car polishing wax

...and that's about it from me. With any luck you should have a perfectly working guitar that looks and works just like before. Next up: Bonus Step - Colouring a Bone Nut.

*The pictures end where they do because I'm still in the process of colour-matching. Damn glitter...

Step 7: Bonus Step: Nut Upgrade

Now if your guitar is on the cheaper end, it's worth taking the time to upgrade your nut. A bone nut will only set you back about a fiver, and it's worth every penny. Only issue is, if you've got cream binding the chances are it won't match. Easy fix, just make up a small glass of coffee and leave it to soak for an hour or so.

Bit of super glue and you're good to go.