Jay and Max are a father-son team of luthiers. They specialize in acoustic, acoustic-electric guitars and ukuleles. Their intonation technology allows for perfect intonation. Check out a gallery of guitars at their website portlandguitar.com.
By Max Dickinson
Today I'll be sharing a new spin on an old technology. An adjustable neck for stringed instruments. This has been around for a long time and is documented in works dating back to the 1800's. There are many ways to achieve an adjustable neck. The most important feature in the design is the choice of using a bolt-on over a dovetail. The dovetail is rigid and can't move. While the bolt-on has bolts that can be twisted. This adds some flexibility to the engineering and makes an adjustable neck possible in a variety of ways. This design is based on Mike Doolin's adjustable neck. In his design the adjustment bolt is on the inside of the sound hole. Meaning that you need to take the strings off to make a change. Ours differs in that it is easier to use with the adjustment bolt having access from the heel of the neck where the strap pin is.
The main idea of the bolt-on neck is to form a tripod of support between the neck heel and the body. In the tripod one of the arms can be adjusted up and down. This changes the break angle and action. A note: we haven't used this in solid body electric guitars because they have many bolts through the back in traditional designs. That is to make it feel more robust. Given that solid bodies are heavy it is nice to have a lot of force connecting those two. Our thin-line hollow body is light enough that we're able to adapt the acoustic method of bolting through the body and the heal of the neck. There are two bolt that are used although only one is load bearing. The second bolt acts to make the neck not flop around while the strings are off. We call it the "feel-good bolt". No one wants to feel like their guitar is falling apart when changing the strings.
Before I get into how it works here is the final product:
This is our stripped-down body. The neck area has a pocket to hold the neck and a pocket for a fretboard support plate to be added.
The inside of the neck pocket has four 3/8ths holes. Three of them have wood inserts. This allows for bolts to be threaded through them. The sides hold set screws that act to adjust the yaw. They have a point put on them to make good contact into the neck. They make sure that the neck stays right in the center. The third wood insert is hard to see and is on the bottom hole. It is added in the opposite direction. This is so that the force of the bolt pulls into the body instead of out of it.
Here it is from the back so know the third insert is there. It is. The fourth hole, the top hole is left free. It has a bolt inserted into it.
Here is a neck in the process. The access hole is right there in the center.
This is the neck from the other angle. There are two screws with wide heads on the sides. They have been ground flat and act as a hard surface for the set screws to press into. The feel-good bolt connects to a barrel bolt in the lower hole. The upper one is our main bolt which will hold the tension on the guitar. It has a pocket drilled out for it then the bolt is inserted, and a wood plug is glued over it. The two blocks near the fretboard act as a spacer for the body so it doesn't pull out the feel-good bolt when tightening.
The neck is attached by turning an allen wrench many times and making the connection. We glue a wood handle onto them to make it easier to turn.
Without the feel-good bolt there is a lot of slop.
Here it is at the maximum tilt angle and the minimum
Then the feel-good bolt is attached. It's looking good inside the body. It's in the top hole.
The results are sound and we're able to turn the adjustment bolt to change the break angle. Here we are at the highest string height
And the lowest
An additional effect of using this is that the fretboard is lifted off the body of the guitar and becomes floating. To some players this provides easier action to those upper frets. I inserted playing cards underneath the fretboard to make this change a little more obvious.
In summary, the way our neck joint works is by having it supported by the tripod of the set screws and the main bolt. Two pieces to be a base and one to provide adjustments. As the bolt is tightened. the neck is pulled further into the pocket. This changes the break angle of the neck and lowers the action. When the bolt is loosened the neck pulls away from the body and forms a triangle with a longer angle. This is how our adjustable neck works. There are many ways to adapt this idea for acoustic and electric guitars. It adds a level of comfort and personalization that can make a playing experience special. If you want to slide one day or shred the next it's an easy change to make. From one guitar many are created.