This is a pretty common but more advanced repair. Steel string “flat top” guitars have over two hundred lbs. of force from the strings trying to collapse the neck into the body. Unlike classical guitars where the neck is part of the head block (they have much lower tension), steel strings were made with a neck separate from the body so that they can be disassembled. Most of the older instruments use a dovetail, either tapered or straight, to attach the neck to the body. A lot of modern luthiers use bolts to anchor the neck. There has been a lot debate about what’s better, but as someone who has built over 50 instruments, half bolt, half dovetail, I can’t tell the difference in tone.
If you lay a straight edge along the fret board on a guitar with a proper neck set, the straight edge will just come to the top of the bridge. A saddle that is too short or too tall will affect the tone and playability. A general rule is about 3/8″ above the top at the bridge position.
A common method in the past was to shave the bridge (not a good idea) or to “slip the block.” This is when the back was heated and pressure put on the neck to “slip” the head block, moving the neck angle. When the back cooled the glue would harden. The problem is that the back was exposed and needed to be trimmed and rebound.
In this example, I’ll be resetting a neck on a guitar by Bozo Podnuavac (pronounced Bo-zho). He gained fame in the 70’s for his flamboyant 6 and 12 string guitars played by people like Leo Kottke.
This guitar had been pretty mistreated. The head stock was broken and poorly repaired. Numerous cracks have been haphazardly repaired and pressure from the neck had cracked the top on both sides of the fret board and moved the head block toward the body.
A straight edge determined that the neck angle left the height at the bridge about 1/4″ below what it should have been.
The first thing I need to do is separate the fret board from the body. This is done by heating the fret board and carefully working a thinned putty knife under the board. I’m very careful about this and don’t force the knife. When the glue is soft it will slide under the board fairly easily. LMI and a few other companies make a silicone heating blanket just for this purpose. Stew-Mac also makes a massive iron with space milled for the frets just for this purpose. In this case I’ll be using the blanket
If the neck joins the body at the 14th fret I pull the 15th fret to make way for two holes I drill into the slot. In a typical dovetail the male portion of the neck is about 5/8″ long and the corresponding female joint in the body is 3/4″ deep. This leaves a gap in the head block and the 15th fret is about 5/8″.
Two tools that I think are essential are from Stew-Mac. One is the guitar neck removal jig and the other is the neck steamer needle and hose.
The other necessity is a cheap coffee maker capable of making steam. I set up the removal jig as in the picture and turn the cappuccino on steam and wait for the unit to heat the water. As an aside always use distilled water or you will have a great deal of mineral buildup. I put a slight amount of pressure on the bottom screw of the jig, just enough to ensure the jig is not moving. The steam works very rapidly to soften both hide and yellow glues. I usually only have to wait 5 or 6 minutes for the joint to loosen. I keep putting slightly more pressure on the bottom screw until the joint separates. I also elevate the bottom of the guitar so that all the water from the cooled steam stays relatively contained. Tapered dovetails remove the easiest but in some instruments the dovetail is straight and they require constant pressure because of the friction.
Sometimes, however the mojo doesn’t work, and this was such a case. After waiting over 10 min. the joint had not budged! I was afraid that the joint may be epoxy. Mr. Podnuavac is still building guitars at 82 so I called him in his current shop in Florida and he did indeed confirm that the joint was a dovetail and should come off.
Take two: This time I put a little more pressure on the screw and after 10 more minutes it did break loose. If you look at the truss rod you can see a grey bar on either side of the truss rod housing. This appears to be epoxy that goes through the head block and under the top. This is what I think was causing the hangup.
Next week. Refitting and re-gluing the neck.