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Acoustic Guitar Neck Re-Sets

by:© Steve Carmody

 

   One of the most challenging repairs is the acoustic guitar neck reset. 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 beak off, soundboards crack, and finishes can be damaged. But a well trained, careful repairman accepts and enjoys the challenge.

   The need for a 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, and 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, note the extent of the problem and make sure there aren't any loose top braces 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.

   Once sure that the only way to regain good playing action is a neck reset, the fretboard extension over the body must be loosened. A heat lamp, heat strip or other heat generating device is 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 made from.

   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 is much trickier. Hide glue is very strong, and dries very crystalline and brittle. Heat alone does not dissolve it so I use a warm , wet palate knife to carefully slide between 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 snap off. Extreme care must be taken not to over heat the instrument.When working with the thin knifes it is all too easy to damage the finish as well as the spruce 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 minutes the 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 should now have access to a small gap between the back of the dovetail and 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. The steam generator of your choice 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 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. Steam can easily damage the finish on the exterior as well.

   

   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. Any of a number of elaborate jigs can be used, and a shop doing a lot of reset may have a bench dedicated just to this purpose.

   With the guitar firmly in the jig the needle is inserted into the fretboard. After a couple of minutes the neck begins to loosen and the 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.With the neck off, the old glue is 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 determine.

   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.