neck set

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. 

Generally… 

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 - 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.

The Reset Button

Neck Reset Acoustic Guitar

The string tension on your acoustic guitar depends on a few factors. String gauge, scale-length and tuning all play a part but if you assume somewhere around 200 pounds of pressure, you'll be in the ball-park. 

If you sat there with 200lbs on your shoulders for years, odds are you might begin to buckle a bit. Your acoustic guitar holds up better than you would but that tension can take its toll. 

If you have any steel-string acoustic guitar for long enough, chances are good it'll need a neck reset at some point in its life. That string tension alters the geometry of the instrument and the most obvious way is that the action creeps up to a point were it's uncomfortable or awkward to play. When a reset will be needed is anyone's guess. Different guitars are, well, different. Could be five years, could be fifty. 

Most guitars have some additional height in the saddle to allow it be lowered, taking the action down with it. This buys some time but, eventually, the same thing can happen. It's not unusual, on older guitars, to see a saddle that's been lowered repeatedly and is little more than a sliver, barely above the bridge. 

Might be a good time for a reset, then. 

A reasonable rule of thumb is that, the plane of the frets should be at the same height as the top of the bridge (that's the wooden bit and not the white saddle). Putting a longish straight-edge on the frets can show you what the story is, as in the photo above. As you can see, it contacts a few millimetres below the bridge-top. Sighting down the frets from the headstock can give you a good idea visually if you don't have a long enough ruler. 

What happens in a neck reset?

Basically, we're trying to re-adjust the geometry of the guitar and neck so that straight-edge in the photo gets raised enough to touch or clear the bridge. That means changing the angle at which the neck joins the body.

To do this, the neck has to be removed and some wood taken off part of the heel. 

Carefully.

A neck reset on a bolt-on acoustic

Ahh, a bolt-on neck…

Dubious arguments about tone aside, if your acoustic guitar has a bolt-on neck, it does make a neck reset a little easier. The first step, you see, is getting that neck off and the easier that is for me, the cheaper it is for you. Bolt-on necks mean less hassle trying to get glue-joints to release.  

Bolt-on neck reset
Acoustic guitar neck set

The first image clearly shows the bolts in the neck block (we're looking inside the acoustic guitar here). Straightforward. Excellent.

The second image is the inside of the 'top'. The image is taken with a mirror lying inside the guitar. It's always a good idea to get an idea what's going on in here before starting major surgery, especially as bolt-on necked guitars from different manufacturers vary in how the handle things in this area. That block of wood glued to the extension and shoulder-brace, for instance, is worth some consideration. 

Guitar Neck Reset
Acoustic Neck Set

A little work to get that block to disengage and some work on the fingerboard extension is all that's needed here. You can see the way neck and body fit together relatively clearly above. 

Something I wasn't expecting was to encounter an epoxy-like material in the body mortice around the neck tenon. It was in the area around that white tape (marked with an X in the photo on the left). Because it wouldn't adhere well to this tape, I'm guessing its job was simply to act as a sort of gap-filler to ensure help ensure a solid connection here. Whatever, I noted it for reassembly and cleaned up the residue. 

Incidentally, I noticed a hairline crack in the heel between the two sockets for the bolts. It was pretty small and probably unlikely to cause problems but I made it good before proceeding to work the wood in this area.

adjusting neck set angle
Accoustic Neck reset

The reset itself is done by removing a 'wedge' shape of wood from the heel—more at the bottom, graduating to none at the top where it meets the fingerboard. Calculating the amount to remove can be done by a relatively simple formula but I tend to do that only to get in the ball-park and then finish by eye. 

The tape in the left photo gives me a line indicating the wood to be removed. There are a few ways to go about this but I like to bevel down to this line and then bring the sides to meet it. 

Guitar-Fix Neck Angle
Guitar-Repair Neck Angle

Like this. Wood is carefully removed from the sides of the heel now. Very carefully. It would be very easy to mess this up. I don't want to remove any wood from that far end where the heel intersects the fingerboard. Doing that would actually move the neck closer to the bridge and muck up the intonation. What we want to do is to take out that wedge shape I mentioned earlier. When that's gone, the neck joins the body at a slightly increased angle and this means better action.

Most of the work is done as shown in the left photo. When the bulk is gone, I'll test fit to the body and I'll remove the remainder of wood using sandpaper between body and neck as in the right image. This helps perfectly shape the heel-fit to the body. 

Acoustic instrument neck set
Repair neck angle acoustic guitar

It's important to check alignment often. As well as the set angle, I'm checking for side-to-side alignment to make sure I don't take too much off one side of the heel. That would point the neck too much to one side or the other—not good. 

Once I'm happy with the fit and alignment, it's time to reassemble. In this case, thanks to the construction of this guitar, it's an easy job. Bolted back on and a little glue in the appropriate places—especially on that little block of wood we found earlier on the end of the neck—and we're good to go.

Neck Reset Acoustic Guitar High Action Fix

And this is what we're looking for. The straight-edge along the frets just skims the top of the bridge. I'll need to make a new saddle to replace this one that's now far too low but that's no problem. We don't need to do any fretwork on this guitar as a consequence of the neck reset (frequently that's not the case) so, all in all, it's been a good day. 

I'll try to pull together some photos of a more involved neck reset soon. Anything with a glue-in, dovetail neck involves messy work, steaming out the neck.

For now, though, I've strung up this baby and it's sounding (and more importantly), playing great. 

I suspect this deserves a celebratory tea.

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.

—o—

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

Cross-posted to Guitarless

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

Guitar Repair: Why Get a Neck Reset

A plane along the frets should hit the top of the bridge—not here

You'll often hear musos talking about a neck reset (or neck set) on acoustic guitars. As this is something that tends to be required on pretty much every steel string acoustic eventually, it's worth understanding why it happens and what's involved in a neck reset.

The top of an acoustic guitar is under a lot of stress. String tension exerts quite a pull on it. Over the years, the wood of the guitar top succumbs to this tension and begins to belly a little at the bridge. This effectively raises the bridge and, with it, the action or string height along the neck. As the guitar ages, it becomes harder to play.

The solution is usually a neck reset. The neck is removed and some wood is removed from the heel to modify the angle at which the neck joins the body. This basically alters the geometry of the neck/guitar to compensate for the higher bridge. It's a pretty big job but one that most acoustic guitars will need at some stage in their life (when depends on a lot of factors) if you own them long enough.

If you think your guitar's action has been (very slowly) increasing over a number of years, you might have a candidate.

I've written an article for Guitarless outlining the reasons and the neck reset process so feel free to take a look - it goes into a bit more detail.

Incidentally, if you're considering buying a used or vintage acoustic, it's worth asking if it's ever had a neck set (which is a good thing if it's been well executed) and/or checking if the guitar needs it. If it does, you should factor that into your bargaining process as it can be a relatively expensive job.