When one arrived at my shop recently, we could immediately see it had problems. Its bridge was bottomed out, yet even with very little relief, there was a 1/4" gap between the top of the 12th fret and the underside of the low E string. This guitar was no longer 100-percent original, as it had been converted from its trapeze tailpiece to an ABR-1 bridge and stop tailpiece years before it reached us. Clearly, by correcting the neck angle on this goldtop, we’d turn it into a more playable and usable instrument. Because of its previous alterations, we wouldn’t be devaluing the guitar in terms of collectability, but rather giving it the life it was originally intended to have.
As I described in last month’s column, removing the neck took a great deal of preparation and patience. We pulled three of the upper frets and drilled six holes in the fret slots. To separate the neck from the body, we had to inject boiling water into these holes for five days, and then apply steam to the sides and underside of the neck heel with StewMac’s Neck Joint Steamer Needle.
The neck came off fairly cleanly, but before I could refit it, I needed to remove some hide-glue residue with a moist cloth and chisel. Then I carefully trimmed the inside lower heel using a chisel, flat file, and a small sanding block that I cut from a sheet of Corian.
To finalize the angle, I used 220-grit sandpaper stuck to the Corian. This made for a very clean and flush heel-to-body joint. During the trimming, I clamped the neck in my StewMac Guitar Repair Vise. Available from stewmac.com (item #1813), this vise features rotating hardwood jaws and a forgiving urethane surface to hold instruments of any shape and size. It’s a must-have for our shop.
LEFT: Resetting the neck angle requires careful measurements.
RIGHT: The Honduran mahogany shim that will determine the neck angle.
LEFT: The finished neck tenon and fretboard wing shims glued in place.
RIGHT: Using a .002” feeler gauge to ensure there’s no space between the reset neck and body.
I referenced the neck-joint fit and angle by going back and forth with the body, using thin mahogany strips as spacers/shims under the end of the tenon as I adjusted for the correct neck angle. After I achieved a quality fit, I held the neck and body together using two grip clamps and a custom-made fretboard-clamping caul. Made of hard-rock maple, my fretboard caul has a 12"-radius bottom surface that’s slotted with channels to accommodate the frets and covered with a 1/16" cork surface.
Next, I tensioned up the outer two strings, checking for neck pitch, vertical alignment, and downward adjustment of the ABR-1 bridge. Once I’d established the neck angle, I cut a Honduran mahogany shim (measuring 1/8" thick x 1 15/32" wide x 4 1/4" long), and sanded it to a minus 2-degree pitch. Then I glued it to the bottom surface of the extended neck tenon using #20 medium Super Glue. I chose Super Glue as the adhesive because the mahogany shim is a permanent addition.
I refer to the section of the fretboard that protrudes out from the side of the mahogany neck tenon as “wings.” My next step was to make support shims to fit between the gluing surface of the fretboard wings and the maple top. I cut and sanded two maple shims (1/16" thick x 3/8" wide x 3 1/8" long) with a 2-degree taper to tuck between the underside of the fretboard and top, and then used Super Glue to attach them to the underside of the fretboard.
To ensure that this stage of the restoration was complete, I used a .002" precision feeler gauge to check that there was a tight seal between the neck and body while under clamping pressure. I didn’t want any open space.
Next month, I’ll show you how I blended in the maple shims and upper surface tenon lip by airbrushing gold to match the top. We’ll also cover what was involved when I finally glued the neck and body together.
If you’re coming to the 2011 Winter NAMM show (held January 13-16 in Anaheim, California), please come say hello to us at booth #3383 in Hall D. This will be a good opportunity to talk shop and answer your Restoring an Original questions. Hope to see you there!
John Brown is the inventor of the Fretted/Less bass. He owns and operates Brown’s Guitar Factory, a guitar manufacturing, repair, and restoration facility staffed by a team of talented luthiers. His guitar-tool and accessory designs are used by builders all over the world. Visit brownsguitarfactory.com or email John at firstname.lastname@example.org.