Martin Guitar: Surprise Dovetail Repair

It’s nice to know that guitars can still surprise me.

I guess.

This one was certainly a surprise. This is a lovely little Martin. It’s in for a neck reset. Looking at the guitar before I started, it was very obvious that the neck had already been off at some point. It wasn’t re-attached terribly well and had been shimmed near the fingerboard as if it had been over-set during a previous neck reset.

So, I didn’t anticipate everything would be factory-pristine in there but I wasn’t expecting this.

What the heck? Martin guitar neck reset throws up a surprise

Huh!? What the…

It’s a bloody-great hole. Look at the close-up inset.

Martin guitar neck dovetail in need of repair

And there’s another one around the other side.

I’m guessing what happened is that the last person to remove this neck didn’t have a good grasp on how to do it non-invasively. He or she removed the heel-cap (that little bit of wood glued to that vaguely-triangular part at the bottom of the heel) and drilled two enormous holes into the dovetail to try to gain access.

To be fair, that heel cap is reattached really well—I hadn’t noticed any evidence it had been off but it must have been.

This isn’t the best way to remove an acoustic guitar neck. Here’s how I perform a basic neck reset if you’re interested.

Make it sound

I can’t just glue this neck back in like that.

Since the holes were drilled, they’re round. A couple of lengths of dowel—slightly down-sized first—will do the trick.

Glue ‘em in.

Acoustic guitar neck repair - Martin dovetail joint

Replacing drilled out wood to repair the dovetail joint of a Martin acoustic guitar

You can See that the near dowel protrudes past the dovetail and into the continuation of the hole in the ‘face’ of the heel.


Anyway, once the glue’s dry, it’s a simple matter to cut away the excess dowel with a chisel.

Now, maybe I can get on with that neck reset. 

Strengthening A Repaired Banjo Neck

Glueing the heel

Glueing the broken heel on this banjo neck is the easy part. Thing is, the tensioning rod can put this glued-in section under a lot of strain so a simple glue-up’s not going to do the trick on its own.

I’ll need to help it out

Section showing how a dowel will be inserted to strengthen the repaired heel

So: Our old friend the spline. In a different form, this time.

I drilled two holes, at an angle, from the heel into the repaired section (being careful not to drill too far and out the bottom—that’d suck).

The dowel ends can be seen (the lighter ovals)

Then, I glued a couple of hardwood dowels in to the holes. The dowels protrude from the ‘good’ section to the repaired section, giving strength to help prevent that section shearing off under tension.

Back together and holding well. Time for tea. 

It's stayed in one piece under tension. Excellent.

Repair To Damaged Fingerboard

Rather invasive repair for cracked heel

This venerable old girl suffered a cracked heel at some stage in the distant past. As you can see, the repair wasn't the least invasive solution that could have been imagined at the time. 

These big-ass screws have kept it (sort of) together but the instrument deserves better. I'm not going into detail on the heel repair here—take my word that it's all glued up and sound. Instead I want to look at how we can minimise the damage those screws have caused.

Damaged guitar fingerboard repair

Damaged guitar fingerboard repair

With the screws removed, things don't look too pretty, do they? Incidentally, the two small holes in the fret slot are mine—I drilled them when trying to steam out the neck to repair the heel and they'll be plugged and covered by a fret. The medium hole is a loose pearl inlay dot that'll be replaced later. 

The holes we're worried about are those big, jagged ones.

Of course, we could squidge a pile of coloured filler into them and smooth off the top but that's not going to be the nicest looking repair. We could cut some plugs and glue them into the hole. If we get a reasonable grain match, that'd be a better option but still not the neatest. 

What we're going to do is to replace the entire section of fingerboard between these two fret slots. Effectively, we're going to remove the rectangular section with the damage and *inlay* new wood. 

A bit of digging around my rosewood stock (and scrap pile) turns up a piece with a similar colour and a pretty close grain match.

Inlay good wood to repair damage to guitar fingerboard


If you look closely in the photo, you can see that I've actually routed out the damaged part but left a tiny sliver along the sides of each side. That sliver will keep a nice contiguous look along the edge of the fingerboard and save messing about trying to match the aged lacquer.

As luck would have it, this instrument needed a refret too. It'd be much more difficult to accomplish this well without refretting.

You can see the new fingerboard wood in the photo below. It's a good match for colour and grain and, once it's all clean and oiled, it looks pretty damn good. Stung up, you'd be pretty hard-pressed to notice anything. 

Much better than filler.

Guitar fingerboard repair

Martin Neck Reset - Easy

About a month ago, I had a spate of neck resets that fought and fought. They just didn't want to cooperate. I'll write something about one of these in a little while but, for the sake of my sanity, I'd like to remind myself that, sometimes, they go well.

If you want a recap on why we reset necks and what's involved, check out my neck reset primer

Getting the neck off

If you’ve a bolt-on neck, life is considerably less messy. If you’ve a dovetail, glued-in neck, well, then we need to break out the steamer. But first, the fingerboard extension.

I apply heat to the fingerboard (carefully, obviously). In this case I’m using a heating blanket. I used to use a shaped metal block that was heated separately and then popped in place but the blanket makes things much more easy. Some poking around with spatulas helps loosen the glue. Often, it'll take a few heating/poking sessions to get things freed up.

Heating fingerboard extension to loosen glue

Loosening fingerboard extension for neck reset

Then the fun begins. Steam.

I remove a fret and drill a little hole, through the slot, into the dovetail cavity. There’s usually a small gap at the back. Once I have access in here, I fire up the steamer and begin to inject steam, through a nozzle, into the cavity. As I do, the hot steam will gradually soften the dovetail glue.

How much steam and how often it's applied varies from guitar to guitar but it's best to use as little as possible. There's quite a bit of wiggling and wrestling with a guitar as I try to get the glue to give up its grip. That wooden contraption around the guitar helps a lot. It provides some 'upward' pressure to help encourage the neck to move out of the dovetail as I wrestle with it. You get a feel for it—when to go with more steam, when to wiggle and, after a while…

It pops out. Brilliant.

Steam to remove guitar neck during reset

Dovetail neck joint disassembled

Setting the neck

Exaggerated illustration of neck reset

The neck angle is altered by taking a 'wedge' of wood off the heel. The image shows an exaggerated view of this—the green section is removed so that when the neck is reattached, it tilts back. 

It's really important not to take wood off the pointy bit of that wedge as doing so would move the neck closer to the bridge and actually alter the scale-length, throwing your intonation all out of whack. 


Chisels and sanding 'sticks' get most of the wood off.  When I've taken off enough to get me close to where I want to be, I finish off by moving to strips of sandpaper. Using then as shown lets me take off the last, smaller, amount of wood but also lets me get a good fit between neck and body. Taking more off one side or the other, during this stage, also allows me to adjust the side-to-side fit so the neck sits properly on the centre-line.

As I proceed, I'm constantly checking the set-angle (by sighting along the board), the centre-line set (by using a long straight-edge along the neck), and the fit between neck-heel and guitar-sides. 


Fitting neck-heel during reset

Checking neck set-angle

Checking neck alignment during reset

Putting it all back together

When everything's right, it's time to reassemble. Generally, the dovetail joint needs to be shimmed as our angle-changes will have altered the way the joint sits together. A couple of test-fits get me where I want to be and then it's time to heat up the glue-pot. In usual Martin-style, the glue goes only on the dovetail joint and under the fingerboard. The heel and body do not get glued on a Martin. This is one of the reasons Martin resets tend to be a little easier.

A properly fitting dovetail pulls itself together. A clamp for the joint and one for the fingerboard is all I need.

Reassembling acoustic guitar after neck reset

Dovetail neck joint re-glued

I like to leave things overnight for the glue to cure—probably overkill but it makes me feel safer. Clamps off and I make a little rosewood plug to fill the hole I drilled earlier. Once that's glued in, I can re-cut the fret-slot through the plug and reinstall the original fret. 

Plugging the 'steam hole'

Plug with slot cut. Will be hidden under the reinstalled fret

Some neck-sets require a full refret afterwards but we're good on this one. Only minimal fret-work is is needed. Also, Martins don't usually need any finish touch-up so this guitar's playing again—with a new saddle and a comfortable action—in no time at all. 

Textbook. Nice.

Neck Reset - The Theory

I’ll have a couple of articles about neck resets appearing in the near future, so I thought it might be an idea to discuss what they are and why they might be needed.

Why would I need a neck reset?

If you have almost any steel-string acoustic guitar for long enough, odds are it will need a neck reset at one (or some) point(s) in its life. Wood settles and string tension pulls the guitar’s geometry around over time. The upshot can be that the action gets slowly higher and higher so that it’s uncomfortable to play.

Often, you’ll find a saddle that’s been lowered, again and again, until it’s just a sliver of bone poking over the bridge. If this is the case, and the action’s still high, a reset might be on the cards.

What happens in a neck reset?

During a neck reset, the neck is removed and the angle at which it joins the body is modified to tilt it back a little. This means it follows the plane of the strings more closely. To try illustrate this, I’ve included one of my, patented, Haze Guitars Hastily And Clumsily-Drawn Exaggerated Diagrams.

On Guitar 1, the action is pretty high. Nobody wants to play Guitar 1 and, when he goes to the beach, Taylors come up and kick sand in his sound-hole. Poor Guitar 1 could use a neck reset.

Why you might need a neck reset and what happens during a neck reset

Off with his neck

The neck is removed so that we can alter the angle at which it connects to the body. We take some wood off the heel—removing a wedge so that the neck tilts backwards a little when it’s reattached.

What we have essentially done is pivot the neck at Point A. In doing so, we’ve moved it so it’s more in line with the plane of the strings and the action is magically reduced. Guitar 1 is transformed into Guitar 2. A shredder picks up Guitar 2 and plays so fast that he spontaneously combusts. All is well with the world.

Is it a big job?

Well, first know that removing a neck generally involves either undoing bolts or steaming glue-joints to soften the adhesive.

Neck resets, therefore, range from relatively-easy (Taylor NT necks), to a-bit-more-hassle (bolt-on necked guitars) to break-out-the-steamer-and-the-tea (Martins), to break-out-the-steamer-and-the-whiskey (Gibsons), to oh-god-not-a-bloody-Guild (Guilds).

Bear in mind, also, that neck resets will often require additional work afterwards. Fret work — likely a fret level or even a full refret is a strong possibility (and the latter may require a new nut too). Some finish touch-up might even be necessary (although this isn't needed too often).

A neck-set should generally be considered relatively serious surgery as it involves some invasive work (in removing the neck) and some potentially disastrous work if the modifications to the heel aren’t performed properly. I’m all in favour of people doing some DIY but a neck set might not be the job for that guy you know who's 'handy'.

Ask around, get some advice and have a good chat to whoever you approach to do the job. It's important to trust whoever you get to do this for you.

Weak Neck Fail

repair guitar neck

This is a particularly handsome Heritage 535. It would be even more handsome if it were in one piece instead of two, though. The neck's come off and a little bit of investigation shows that it never stood a chance. This neck joint was weak from the start.

These joints are referred to as 'mortice and tenon' joints. In this case, the tenon (the bit at the end of the neck) was too small for the mortice (the 'pocket' in the body). As well as having a relatively large shim on one side, the tenon didn't make contact with the bottom of the pocket. There's an gap of a couple of millimetres between the two.

You can see the circled bits in the image. On the left is a chunk of mahogany from the tenon that's split off and the glue line is visible on the right. You can see the gap.

That gap means no glue joint there. Only the sides are glued (well, those and the 'face' of the joint but that's not providing a lot of strength).

This is a weak neck joint that was much more prone to fail that it ought to have been.

Rather than just gluing it back together, I'm going to build up the tenon to get this joint to where it should have been from the factory.

guitar neck tenon break
neck joint failure repair

First off, that little chunk of mahogany that's still glued to the side of the neck pocket has to be removed and glued back to the neck tenon. Once that's done, I nab a new bit of mahogany and thickness it so that it will fill the gap.

In the right photo, you can see I've glued this on and cut it to match the shape of the existing tenon. The thickness of the added wood gives you an indication of how much of a gap there was.

fix guitar neck joint
repair guitar tenon joint

I removed the old glue from both parts and re-glued the neck to the body. Because the break was quite clean, only a little touch-up work was required to get the guitar looking its best.

This repair looks good and, importantly, has actually resulted in a better, more sound, neck joint than when it left the factory.

Les Paul Neck Removal and Repair

les paul broken neck heel

Yikes. If you've been reading my stuff for a while, you've probably spotted a few different examples of neck breaks. Most of these have been up at the headstock end as that's the more likely place for a break.

It can happen down the other end too, though. This Les Paul took a tumble and broke in a nasty way. The exterior damage is obvious but it's pretty certain that crack extends into the neck tenon too (the tenon's the bit that gets glued into the neck pocket in the body).

This neck needs to come out to be properly repaired.

It's not too often that I need to remove a Les Paul neck, which is lucky as it's a relatively involved job. With a strong cup of tea to steel myself, I set to work.

les paul heel repair frets
les paul neck removal

First up, a few frets need to come out. To remove this neck, I need to soak and steam the glue out and that means getting access to the internals of the neck joint. I do this by drilling small 'access' holes. These are drilled in the fret slots. When it's all done, I'll fill the holes with rosewood plugs and re-cut the slots. All of this is hidden by the refitted frets.

Your eagle-eyes will have noticed a little dot on each (numbered) fret. These frets will be refitted and the dot tells me which is the bass end.

Keeping fingers crossed, I take a look under the neck pickup, hoping for a long tenon. No luck. If I could have seen the end of the tenon, I'd know exactly what size it was so I could position my holes to accurately access the sides of the neck joint  (if it's not clear what I mean here, a photo later on might clarify things).

Since all of this tenon is hidden, I have to measure out the usual Gibson size and position for this guitar and hope that it's built properly to spec.

In the photo, above on the right, you can see the pencil marks I've used to plot out the tenon and the holes I've drilled to get access to the joint.

gibson neck removal
steaming off gibson neck

This one's a bit weird-looking, I'll admit.

In the left image, I'm using a syringe to insert boiling water into the holes I've drilled. I give it a few seconds and then suck it back up again. What comes out is cooler water with some manky-looking dissolved glue. I repeat this process a lot over the course of a couple of days. A Les Paul neck joint is a hell of a strong joint and doing this gives me a little bit of a head start before I hit it with the steam.

Which is what's happening on the right. That nozzle lets me get piping hot steam deep into the joint. The heat and moisture helps to dissolve more glue and, after some time and work, the glue eventually lets go…

les paul neck tenon
les paul neck joint repair

…Leaving most of the bloody tenon still in the pocket. D'oh!

The heel crack extended into the tenon as we thought. Now I have to keep working to get this piece out with pretty much no leverage.

More tea required, I think.

Some steamy swearing later and it's out. Now, in the side of that neck tenon, you can see the tracks of those holes I drilled earlier. We were right on the money with the positions too—nice.

gibson guitar neck tenon repair
les paul neck joint fix

And here's the jigsaw we need to get back together. You'll notice a small shim in the neck pocket. This was installed at the factory (it's not uncommon) and I'll reuse it for this repair.

All of the old glue is cleaned from the mortice and the tenon and then, the two bits of neck are glued back together. Again, the tracks of those access holes are clear in the photo on the right.

gibson neck tenon repair
les paul repair touch-up

Once it's sound again, the neck is reattached to the body. Those frets are reinstalled and all the frets are levelled to ensure clean playability.

Then, it's just some touch-up to hide the evidence. As the rear and neck of this Les Paul are black, the opaque colour easily disguises the repair.

It took a bit of thought, a lot of work and twelve buckets of tea but this job's a good 'un.

Guitar Repair: Acoustic Neck Break (Reassembly)

Instrument Repair Dublin

A little ways back, I discussed the removal of an acoustic guitar's neck for repair. I also talked a little about my opinions on the construction of that particular guitar. The neck-removal post was getting a little long so I decided to split out the reassembly part. Putting an acoustic guitar back together generally involves some glueing. Sometimes more and sometimes less.

A bolt-on neck will generally just require that the fingerboard extension (the part past where the neck meets the body) be glued to the guitar top while the bolts inside will handle the job of pulling, and securing, the neck into the body.

A dovetail neck joint requires this but also needs glue in the joint itself. Depending on the manufacturer, the face of the heel (the flat portion that butts against the guitar side) may be glued too. Some guitar makers (Martin, for instance) don't apply glue there while others (Gibson for example) glue it. This is one of the reasons it's a bit more work to perform a neck reset on a Gibson.

Fix acoustic guitars-Dublin
20110618 IMG 1212 small1

In the case of this particular guitar though, the heel face is entirely flat and is all a glueing surface. The steel box-section tenons must also be glued into their corresponding mortice (channel) in the top and the fingerboard extension must be fixed to the guitar top.

Complicating matters is the fact that there is no force that would pull the neck into the body in the same way as a dovetail or bolt-on joint would. This means I had to clamp the neck into the body in some fashion while the glue cured.

Some inventive clamping-caul making later…

And I had a wooden caul that would fit the curved heel, letting me clamp the neck into the body. Ready to go. I did a couple of dry-runs with no glue as this was a tricky clamping job. When I was happy I could get the clamps on quickly and accurately, I went for it.

Guitar Neck Repair
Stringed Instrument Repair

That clamp in the photos—running from the soundhole to the heel—wouldn't normally be required but this instrument's construction made it necessary. The clamp doesn't actually contact the soundhole edge but I've got a piece of linoleum there to play it safe.

Once the glue's properly cured, it's ok to unclamp. I replaced the fret I removed (see the previous post) to help steam off the neck, made sure it was secure and level and I strung this little fellow up to make sure it played well.

This job was a little more involved than it might be on a different guitar. All that's not important though. What's important is that this guitar is making music again. That's always good.

Cross-posted to Guitarless

Guitar Repair: Acoustic Neck Break (Neck Removal)

Fix Acoustic Guitar Neck

In a previous post, I gave my opinion on what I saw as the problems with the neck-joint design of a guitar I'd recently worked on. I thought you might be interested in some more detail about that repair (without my whinging about design issues). While some of the steps undertaken in this repair are common with any job that involves removing a guitar's neck, you might find it useful to, first, check out some of the ways in which this guitar differed. The guitar had taken a knock and its neck had become detached at the heel. It still appeared to have some attachment towards the guitar top but it wasn't easy to see what was going on. Internally, there was quite a small neck block—too small to accommodate a dovetail—and no sign of bolts although the feeler gauge I inserted seemed to indicate something bolt like. It actually took a chat with the manufacturer's customer service to sort it out. There were no bolts or dovetails—dowels were used to align the neck and the joint was a mortice and tenon.

Fixing a problem like this on a guitar isn't just a matter of squirting some more glue in and hoping for the best. A proper job requires that the joint be disassembled and cleaned. If this isn't done, the new glue will not penetrate properly and will only adhere to the older, failed glue rather than to good, strong wood.

Acoustic Guitar Neck Repair
Fingerboard Removal in Guitar Repair

Removing an acoustic guitar neck involves softening whatever glue is holding the neck to the body. A dovetail requires holes be drilled into the joint so that the glue can be softened by carefully injecting steam. That's not required for a bolt-on neck, of course, but what is common with all joints—including this one— is that the glue holding the fingerboard extension to the guitar's top be loosened. We do this by applying heat.

Sometimes that heat is applied using a cast block that I heat on a hotplate. For some jobs though, I use heating blankets. These are much more controllable but you still need to take care. The blanket is clamped—loosely—to the fingerboard extension and I keep a very close eye on it. When I judge that heat has penetrated the board and begun to soften the glue I remove the blanket and get to work with the palette knives. It's a delicate job as too much pressure could easily tear into, or lift grain from, the guitar top underneath. It's often necessary to heat the area a couple of times to separate the surfaces.

Once the fingerboard extension is loose, the neck removal can begin. As I mentioned, on a bolt-on this is an simple as undoing some bolts while a dovetail would need the joint steamed loose. On this neck, removal was complicated because of the construction.

Fix Acoustic Guitar Neck
Instrument Repair - Acoustic Neck Repair

You can see from the images that the neck has two steel box-sections protruding from the heel. These were glued into the corresoponding channels in the guitar top. I needed to get this glue to soften too but the heating blanket wasn't going to do the trick. It was necessary to use a similar technique to that used for dovetail disassembly. I removed one of the frets on the extension, drilled a couple of small access holes and injected steam (very carefully—these are small channels very close to the guitar top).

This process, too, was made more difficult than on a traditional construction. Because of the alignment pins, I could not remove the neck from the body vertically. Instead, I needed to 'pull' the neck away from the side. It made for an annoying job as it's really hard to get any leverage or apply pressure well.


As this is becoming a little long, I'll cover reassembly in a future post. Oh, the suspense…

Cross-posted to Guitarless