The drawbar is something I have very shared opinions about, you could say I don't like it. From the day it was invented in the 1930s, it has hung and shaped the guitar's design. With a drawbar you can make long thin necks that hold for coarse strings and high strings. Without stiffening in the neck, the wood must be of the highest quality and preferably V-shaped and thick to hold for coarse strands and long necks. You also get the opportunity to adjust the neck bend in the middle with a drawbar which is very comfortable.
The main disadvantage is that the metal bar is both heavy and lifeless in terms of sound. As almost always, it is the sound and tone of the guitar that suffer for convenience. Another problem is that the drawbar is far from working as well as people think it does. Since wood is always variable, the neck will not get the nice even bend you want if you tighten or release it, instead the neck will get both hills and valleys along the neck. Sometimes much less. In addition, the whole effect will not come at once, the neck will tighten for a week after the adjustment. You can easily have problems with strings on parts of the neck if you want low string height after an adjustment, here can tenths or even. Hundreds of bumps make a difference.
The alternative to thick and short neck in wood or long and thin neck with drawbar with all it means is to use carbon fiber to give the neck sufficient stiffness. Carbon fiber is extremely rigid, lightweight and has a good acoustic tone. Also good for long-term loading, a curved carbon fiber rod goes back to being straight even after long-term bending. All GammelGura get a carbon black square tube in the neck with a birch round bar that fills the hole in the middle. With the stiffening, one never happens that a soft neck becomes banana-shaped when the strings are tuned. The neck will also remain stable for a long time without bending. A hollow square tube is half as heavy and almost as stiff as if it were solid, but goes off faster if it bends sharply. The last is no problem glued into a neck! Enjoy the variation when using as much wood as possible 🙂
Even if the carbon fiber rod is extremely stiff, the neck will bend a little grand from the string pull. You always get an extra large bend closest to the upper saddle, call it a "cooker hook". This is partly because the neck is the thinnest at the top and you get a rotational force from the breaking angle of the strings at the upper saddle. How much bend you get in the neck and at the top depends on how soft the wood in the neck is and how strong the slope is on the head in relation to the fretboard. The carbon fiber rod ensures that the variation is kept to a minimum between soft and hard necks, on a parlor with 12 straps to the body, a hard neck actually manages to withstand the string pull without carbon fiber rod. If the neck is soft, it does not. A carbon fiber rod is an insurance and does not adversely affect the tone.
In brackets, a stiff neck is good for both the sound and volume of a guitar, less energy is lost on the way to bending the neck back and forth if it is stiff. A soft neck is never good for practical reasons (but may sound good, although a little weaker), but not an extremely stiff neck is good either. You need to get some variation in the tone of the throat movement, with a really stiff neck the tone becomes clinical and boring. Which is always the best.
My solution is to grind the grip board to a small relief in the position that the neck gets when it is loaded with strings before banding. After the banding, the bands are crowned in the same way in the position the neck gets under tension. You are thus given two chances to give the neck / grip board (or rather the tops of the straps) the correct shape. If you do not shape the board first, you will need to sand the straps a lot, especially near the top saddle. The two-step method has got the right shape even before the bands are crowned.
In order for the neck to bend properly and not give more than it, temporary bands should be knocked into the grooves up to the 12th band. No adhesive is used and the straps can easily be removed without damaging the grip board.
Also fixes the underside of the skull at the top with a few wedges and tightens a clamp to hold the neck sideways. Now the strings can be strung with guitar and neck in the same position as with strung strings.
Edit: Nowadays I use CNC milled aluminum beams with different reliefs instead of Katanan which did not give the perfect bend I thought (the same phenomenon as regular drawstrings!).
When the guitar is detached from the jig, the neck curves slightly in the middle and has an extra small bend closest to the upper saddle, the softer the neck the larger the bend. Everything will be just as it should when the strings are tightened! In the best of worlds, you will never have to adjust your neck and you will not miss the drawbar. Meanwhile, the guitar sounds better than if it had a 😉