Introduction: Resetting the Neck on an Acoustic Guitar
An acoustic guitar, which is almost always constructed from different types of wood, is subject to slight dimensional changes due to temperature, humidity, aging of the wood, and frequency or intensity of use. One of the dimensions that can be affected is string height or “action”. This is the distance of the strings from the frets. If it is too low, the string will buzz when being plucked. The buzzing is caused by the string vibrating against a fret further down the neck. If the action is too high the guitar can be difficult or uncomfortable to play because the strings are hard to press down or it is difficult to keep fingers from touching an unwanted string.
It may be that the guitar was originally constructed so the action is off. The truss rod adjusts tension in the neck and can be used to adjust the action by slight amounts. The strings put tension on the neck causing it to bend slightly, raising the action. The truss rod tension prevents or minimizes this bend. There may not be enough adjustment in the truss rod to correct the string height on your guitar, as was the case with mine.
The neck needs to be "reset".
Step 2: String Height
My guitar is one that I built from scratch. The neck angle with respect to the guitar body was off, which caused the string height to be too high. I played it for a while until I couldn’t stand it anymore. I tried adjusting the truss rod and shaving down the saddle, which is the little bone piece in the bridge that the strings are stretched across. Still the action was too high. I measured the height of the low E string at the 12th fret to be 4.8 mm. Typically a very low action would be about 1.6 mm and a very high action would be 4.0 mm.
Step 3: Checking the Neck Angle
I decided to remove the neck and shave some wood off the base that touched the guitar body to change the neck angle, i.e. make it fall away from the body at a sharper angle causing the strings to become closer to the frets. The angle can be checked by laying a metal ruler on the frets extended to the bridge. The ruler should just skim the top of the bridge if the angle is correct.
I also hoped to correct a small gap between the neck base and body that appeared.
Step 4: Neck Attachment Methods
Guitar necks are usually attached with bolts or a dovetail joint. Luckily I had decided on a bolt on neck when I built my guitar, making removal much easier. Removing a dove tail neck requires removing a fret and drilling small holes in the fret slot to get at the joint to work it loose.
Step 5: Removing the Neck
I removed the strings and began the work of removing the neck, resting the guitar on a piece of cardboard at my dining room table. The fret board is glued to the guitar sound board (top) just above the sound hole. The glue used is typically hide glue but I used Titebond which is more difficult to cut through. I used a heated putty knife to slide between the sound board and fret board to break the glue joint. I first rounded the square corners of the knife and sharpened the leading edge with a grinder. A soldering iron was used to heat the putty knife. I began to work the knife under the fret board, gently tapping with a hammer and reheating frequently. Care should be taken not to let the knife handle scrape against the soft wood of the sound board. I added a little Willie Nelson to my guitar when I accidentally let the putty knife handle press a dent or two in the soft sound board wood.
Step 6: Marking the Neck Base
Once the glue joint was sufficiently severed, I unbolted the neck and removed it. With the ruler on the frets, I held the neck back in place on the body and tipped it back until the ruler just skimmed the top of the bridge. I noted the size of the gap and scribed a line on the base of the neck corresponding to the amount of wood that needed to be removed. A more precise method would be to use calibrated shims, but I just eye-balled it.
Step 7: Re-attaching the Neck
Once the mark was made , used a chisel and dremel tool with a mini sanding drum to remove the wood, frequently checking the fit as I progressed. When I was satisfied with the fit and angle I lightly sanded the bottom of the fret board, applied more glue, bolted the neck back on and used a C-clamp to secure the fret board to the body.
After letting the glue dry for about 24 hours, I removed the clamp. I also used this opportunity to apply more lemon oil to the fret board and another coat of Tru-Oil to the sound board. New strings were installed and I checked the string height of the low E at the 12th fret again. It was just over 2.0mm. The guitar had a slight string buzz on the low E string at the 13th fret which I will likely correct with truss rod tension or by installing an new, slightly taller saddle.
The guitar is now much easier to play and even sounds better.
It’s like having a new guitar!
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