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. 

Gibson Neck Reset - Curveballs

The last word on neck resets for a little while. We've had the theory. We've had the straightforward neck set on a Martin and we've had the Martin neck reset that fought back a little. 

Let's take a look at a neck reset that threw up some curveballs along the way. 

On a Gibson acoustic guitar, the job of getting the neck off is generally a little more work. As well as glueing the actual dovetail joint, the folks at Gibson also apply glue to the surfaces between the neck-heel and body-sides. Also, they glue the neck in and then  lacquer neck and body together. This means getting through the lacquer safely when removing the neck, and—more often than not—means some light finish repair work after it's all reassembled. A Gibson is more work to reset but is still generally straightforward. 


First up, this guitar has a couple of longitudinal cracks in the top. These have been there a while and have had a previous repair before I got the guitar. I check the repair and it seems sound so I move on. I also note that there is a small gap between the bottom of the heel and the body-binding. I can't tell too much about this now and it's clearly been there for some time so I pop it in the mental notebook.

I won't go into detail as I've covered much of this before. I free up the fingerboard extension, drill my steam access hole and get to work. 

Something's not right.  

As soon as I give the instrument its first 'encouragement wiggle', I can tell that something is wrong. 

Applying steam to loosen glue on neck dovetail

Applying steam to loosen glue on neck dovetail

Neck block has come loose internally

After some investigation, the issue becomes clear. The neck block (the solid hunk of wood that supports the neck inside the guitar) has become loose. The guitar's top and back are no longer glued to the block and any pressure I might apply to remove the neck is also going to push the block up against the top until it breaks.

It seems likely that the existing top cracks happened either because the block was loose and not properly supporting the top or (more likely) occurred at the same time as the block became loose—probably in a fall. Either way, I don't want to make things worse. 

You'll notice in the photo above right that I've removed the fingerboard extension (and that palate knife shouldn't be able to slide in like that). However I proceed on this job, I need to re-glue the neck block but I'm now concerned about unduly stressing this guitar top any more than is completely necessary. Removing the fingerboard extension will allow me to support the top as I remove the neck. 

Re-glue acoustic guitar neck block

Supporting guitar top while removing neck

You can see that support in the photo on the right. The dovetail-shaped slot cut in some plywood lets me ensure that the top doesn't move as the neck joint is separated. That separation is a slightly slower job now, and a more careful one.  

Once the neck is out and I've cleaned up the joint, I can glue the fingerboard extension back on to the neck (using a sliver of rosewood to take up the space of the fret-slot I used to cut through. This slot will be re-cut after things are back together. I go though the normal neck reset process from here.  

Dovetail and socket 'mismatch'

This Gibson has one more curveball to throw at me though. As I alter the neck angle, the bottom of the joint becomes looser in its socket than I'd generally have expected (a little is quite normal). Turns out, this dovetail's not the best fitted joint I've ever seen. The dovetail (the male part of the joint) is quite a bit shorter than the socket it mates to. I'm going to hazard a guess that this may have contributed to that little gap between heel and body-sides I mentioned earlier. 

Not a major problem. Some shimming is pretty much always necessary during a dovetail reset. Done properly and I've got a heel that contacts perfectly all around.

Better than original. Nice. 

Martin Neck Reset - Hard

Martins are generally quite nice guitars to perform neck resets on. They're usually well made and the way they construct their instruments makes resetting a little more easy. 

Martin applies finish to necks and bodies separately and then assemble them, so there isn't the same risk of lacquer chipping and cracking when the neck is removed. Also, Martin applies glue to the interior of the dovetail joint and not  between the neck heel and body. This is more than sufficient to give a strong joint and makes it easier to disassemble. 


Except when it's not.  

Very occasionally, I'll come across a Martin that is the exception to the rule Maybe it's a Monday-morning-guitar thing but sometimes the guitar gods throw you a curve-ball. 

Check out my last post on Martin Neck Resets for the 'right' way for the job to go. I'm not going to go over all that information again—I'll just talk about that curve-ball I mentioned. 


Martin dovetail joint with a LOT of glue

Dovetail neck joint - body-end.

This neck-joint had a lot of glue.  Seriously, a LOT of glue. The arrows in the image above show that there was tons of glue on the 'cheeks'—the part that contacts the side of the guitar body. This isn't a major problem (lots of manufacturers—Gibson for instance—make this a glueing surface) but it does slightly complicate an otherwise straightforward Martin reset. If I didn't know better I'd have said this neck had already been off and re-glued but there were no signs that was the case.

Further complicating things, there was no gap at the back of the joint. There's usually a small gap between the male and female parts at the back of the dovetail and this is a nice access point to get steam in. Not so lucky here. 

I ended up having to drill a few holes to try get good penetration for the steam all over the joint. This made for very slow going. You need to be careful as you obviously can't see inside the joint until it's disassembled. 

Sometimes guitars fight back. This one took a lot of wrestling, a lot of steam, and a lot of swearing.  

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.

Mass Manufacture Acoustic Neck Joints

I should definitely preface this post by stating that what follows is my opinion only. It may be that I'm alone in these views or it may be that other guitar builders and repair-techs agree. The post below, however, is my take on things. I recently had a Tanglewood TW130 through the shop for repair.  It's a nice little acoustic—I've always been a sucker for all-mahogany acoustics. The guitar had taken a fall and the heel had come away from the body. I'll detail the steps taken to assess and repair this damage in a later post but I wanted to discuss the guitar's construction as a separate issue.

Before I get to that though, a little primer on 'usual' acoustic guitar neck joints. Bear with me…

The Traditional Dovetail Neck Joint

Acoustic Neck Repair Dovetail

Acoustic Neck Repair Dovetail

Historically, acoustic guitars had their necks fixed to the body with a dovetail joint. This is a very strong joint and when glued is damned solid. The dovetail is considered the 'traditional' neck-joint and it tends to be more prized by many who consider it imparts a superior tone to the guitar. A good dovetail joint tends to require a little more work and care to accomplish well though, and it makes for a little more work when performing a neck-reset on an older guitar.

The Bolt-On Neck Joint

Acoustic Neck Repair Bolt on

Acoustic Neck Repair Bolt on

For these reasons (and possibly others), many modern guitar makers use a bolt-on neck joint. In this joint, a short mortice and tenon is cut in the neck block (in the body) and in the neck. This is used mainly for alignment purposes although it provides some strength. Most of the joint's strength, however, comes from the bolts that are attached, through the neck block, into threaded sockets in the neck heel. These tighten to pull the neck securely into the body and, questionable arguments about tone aside, provide a strong, solid joint. And, when it comes to setting the neck at some stage in the future, it's much easier to undo some bolts than it is to steam out a glued-in dovetail.

The New Neck Joint?

This Tanglewood doesn't use either of these methods, however.

Acoustic Guitar Neck Joint Repair
Acoustic Guitar Neck Repair

This guitar has a quite small neck block (the part that the neck usually bolts or dovetails to) and has a slightly larger than usual support under the fingerboard extension. The reason for this latter is that there are channels cut here to accept the truss-rod (in the middle) and two square, box-sections of steel on either side.  It's these steel sections that—glued into the channels on top of the guitar—that provide the bulk of the joint's strength.

You can see three dowels poking out the front of the neck block/body—one of these is wooden and two are plastic. In my opinion, their primary role is alignment as they're not going to provide much support.

The face of the neck-heel—where it butts against the body—is a glueing surface on this guitar and I guess this was considered sufficient support when combined with the dowels and channels. I've a couple of problems with this.

  • String tension does a mighty fine job of trying to pull the headstock of a guitar down to meet the bridge. Poor support along the heel area can only make this job easier. Think of a long-bow. The tension of the bow-string pulls the bow into that arched (bow) shape. That's what the strings are doing on your guitar too. The poor thing needs all the help it can get to resist those damn strings. One knock was enough to break the (slightly brittle) hold this glue had.
  • Dovetail and bolt-on neck joints both pull the neck snuggly into the body. As well as strengthening the joint, this can only help tone and string energy. The Tanglewood's neck is, effectively, sitting on the body with a bit of glue and a couple of pins holding it in place.
  • While it's fair to argue the practicalities of the owner of a lower-cost guitar deciding to plump for a neck-reset at some stage in the future, should that happen, legitimately disassembling this sort of joint would (perhaps counterintuitively) be much more problematic than what was achieved with a simple fall in this case. As it happens, reassembly is more difficult too.

Now, I'm not being elitist here. This is not a guitar that cost thousands and there are many valid reasons for manufacturers to economise where they can. I've owned, played and repaired many cheapies and budget instruments in my time and many have been absolutely fine (and some have punched brilliantly above their weight). I've no idea how much money was saved in the manufacture of this instrument in this manner rather than with a regular bolt-on neck and I'm slightly conflicted in passing judgement as it's great the there is now such a selection of fine instruments available for peanuts. It certainly wasn't the case when I began playing guitar.

Personally, though, I can't help feeling that the decision to go with this joint over a regular bolt-on has compromised this instrument. At very least, I feel it's durability, and therefore longevity, is compromised. I don't think that's a good thing on any instrument, no matter how much it costs.

What do you reckon?

Cross-posted to Guitarless