Acoustic Guitar Neck Re-Sets
by:© Steve Carmody|
One of the most challenging repairs is the acoustic guitar neck
A neck reset is an invasive job which requires both skill and guts to execute
correctly. To be able to do a clean neck reset is an accomplishment to be
proud of. A misstep can destroy an instrument. I liken resets to heart
surgery, the patient is usually in distress, non-functional. If the operation
is a success the patient will have a new fulfilling life, but the patient
could also die. Well, in most cases a guitar cannot be killed from a neck
reset gone awry, but neck heels do break off, soundboards and sides can crack,
can be damaged. But a well trained, careful repairman accepts and enjoys
the challenge. In the following article I will be discussing a number of aspects related
to the removal of a neck from a CF Martin guitar, but most of the elements also apply to
resetting the neck of any guitar with a glued neck joint.
The need for a neck reset is indicated by high string action,
and no means
to adjust out of it, i.e. the saddle is as low as it can go. For most players this will mean that,
the height of the low E string,
as measured from the top of the 12th fret to the bottom of the E string,is 4/32" or greater, with the saddle set as low
as it can go. On necks
that have adjustment rods, the neck is showing little or no relief. In essence,
the relationship between the neck and the body is out of wack. In most cases
the neck is not pulling up so much as the top of the guitar, in the area
of the bridge has pulled up over time.
The first step
is to evaluate the guitar
and make sure there aren't any other issues contributing to the problem.
A loose top brace could allow the top to lift, causing high action, but
when reglued could bring the action back down. Similarly, a loose bridge can cause high action.
Once sure that the only way to regain good playing action
is to perform a neck reset, the first step is to seperate the fretboard extension over the body.
A heat lamp, heat
strip or other heat generating device is generally used to warm the glue joint between
the fretboard and the top. It is a good idea to cover the top with a heat
reflecting material. In photo 2 I use a material that firemen's suits are
On guitars made with white glue,
the heat turns the glue to gel rather
quickly and it is easy to then slide a thin palate knife into the joint to
separate the fretboard. On guitars made with hide glue the job can be much trickier.
Hide glue is very strong, and dries very crystalline and brittle. Sometimes a thin tool
can slide into a hide glue bond and break right through. But heat
alone does not soften hide glue so a bit of water must be introduced if the desire is to soften it.
When necessary, I use a small amount of warm water on the palate knife to soften the glue and enable me to carefully
seperate the joint.
Once the joint begins to separate I sometimes slide thin
wedges of wood in to keep
the joint open, mindful not to put too much pressure on the fretboard which
could crack. Additionally, care must be taken not to overheat the instrument.When working with
the thin knifes it is all too easy to damage the finish
as well as the wood of the top in the area of the fingerboard during this operation. Additionally, other
glue joints can be weakened by the heat.
If your karma is good (and also your customers) after a few
fretboard is separated from the soundhole up to the 15th fret (assuming 14
to the body joint). The next step is to remove the 15th fret and drill a
hole in the slot. On most Martin guitars you will now have access to a
small gap between the back of the dovetail and the pocket of the neck block. On other
guitars, who knows?
The idea now is to loosen the glue in the neck joint and
then slide the
neck off. Warm moist air generated by a pressure cooker is the method I
use to loosen the glue. My good friend and mentor Mark Glickman used a stove
top espresso maker. In my shop the pressure cooker sits atop a hot plate.
A flexible hose is attached, at the end of which a reducing valve with a
hollow pin (I use an inflation needle) is mounted. Once the cooker is heated
and shooting steam out the needle, the needle is inserted into the hole you
have drilled in the 15th fret slot. Just how much steam and how long the
needle is left in the guitar is variable. Too much moisture in the neck
joint for too long will expand the wood and lock the neck in. Too much steam can destroy the
finish of the neck or the guitar body. Too little
and the glue will not soften. Each case is different, but only as much exposure
to the heat and moisture as is necessary is the ideal.
In most cases the neck is not falling off prior to the neck
set and is
tightly seated in the dovetail joint. The neck will have to be pushed off
ever so gently, but firmly, once the glue is softened.In most cases, I find that I can
slowly work the steam softened neck joint loose and then slide the neck off by hand. But sometimes a very tightly
fitted neck will have to be pushed off with the use of jig designed specifically for the
this purpose. There are two common styles of neck removal jigs. One is essentially a rack
which mounts to the body, the other is a larger bench-top jig. In both cases a screw press the neck
off while holding the body in place.
When using one of the jigs, the guitar is mounted into
the jig after
the steam has begun to loosen the joint. Pressure is
applied to the heel by the screw mounted on the jig. If everything goes
right the neck slides off. Sometimes the neck POPS! off, so you have to
be ready to catch it. If things aren't going well, the neck doesn't budge.But in most cases, with
with persistence and a bit of finesse, the neck can be worked off the body.
With the neck off,
most of the old glue can be cleaned up before it dries. The body and neck are left for at least a day to dry.
Now the actual "resetting " begins. The previous neck angle was reflected by the relationship of
the plane of the fretboard to the body. This plane is largely determined by the angle of the heel
of the neck where it joins the body , (generally at the 14th fret). Therefore, to get a greater
tilt away from the top, wood must be removed from the heel starting at the heel cap and moving towards
the 14th fret (assuming a joint at the 14th fret).
This is done with a razor sharp chisel, files and sandpaper. More wood is removed from the heelcap
area and the cut is tapered so that nearly none is lost from the point where the fretboard and neck meet. In essence the heelcap becomes smaller, the neck tilts back, therefore the strings sit closer to the fretboard. A taller saddle can then be fitted in the bridge until proper string height over the frets is achieved.
After a process of fitting, refitting, and making the exterior neck body joint as clean as possible
( no gaps), shims of mahogany are glued into the neck block cavity to secure the neck to the body.
Sometimes, on necks which require a radical set back, a shim may also be placed between the
soundboard and the top to avoid a hump around the 14th fret.
Finally the joint
is glued and clamped. If all has gone well the
guitar can be strung up and played the next day. Judging how much wood to remove is part science
, part experience . I never reset a neck without a proper bridge in place on the top. The correct
angle is determined by the bridge height plus the desired saddle height above the bridge, plus,
an estimate of how much the top will lift under tension. This is very important, and very tricky to
Neck resetting is very challenging. Only a repairman who has
seen it done many times should ever try it on a guitar he does not own. And even then, think long
and hard before you do.