Quote:
Originally Posted by H165
Questions concerning my current guitar build. Any help, comments, information will be greatly appreciated. If there is an existing thread on this subject please point me to it.
The areas I am interested in are the "faces" of the guitar body and the neck when these two components are separately made and then later joined.
It appears to me that a "good, tight uniform fit" is required at this joint. The problem is, I do not know exactly what a "good, tight uniform fit" means. I stipulate the basic physics: the forces on the faces is equal to the forces applied by the dovetail wedge action or the fastener faces. My basic question:
What is the optimum final face-to-face pressure of an acoustic guitar neck-to-body joint?
The related mechanical questions for the two most common joints:
1. What is the optimum final face-to-face pressure of a glued-and cured dovetail joint?
2. What is the actual final face-to-face pressure of a glued-and cured dovetail joint from any specific manufacturer or builder?
3. What is the optimum final face-to-face pressure of a bolted/screwed joint?
4. What is the actual measured final face-to-face pressure of a bolted/screwed joint from any specific manufacturer or builder?
5. What is the measured joint clamping pressure required to achieve the optimum final face-to-face pressure of a glued-and cured dovetail joint?
6. What is the measured torque in inch-pounds per fastener required to achieve the optimum final face-to-face pressure of a bolted/screwed joint?
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First, there's no way to measure any of those forces accurately.
The traditional dovetail joint isn't about creating force as much as simply providing a well-fitting joint that provides a small amount of clamping force once the glued faces of the dovetail are drawn together. It's actually easy to cut the joint so close that it locks the neck to the body BEFORE it gets all the way to it's seated position. There are a ton things to go south when a traditional dovetail is used, and even more down the road when repair eventually becomes necessary. It's the reason why so many builders have opted for the easier to manage bolt on M/T joint.
Years ago Bob Taylor reasoned out the NT neck joint, which provides a solid joint that's easy to manufacture, fit, and later adjust and work on. Taylor could just as easily produce a "perfect" dovetail using their CNC technology, but doesn't. That should clue us in to the sham that dovetails are.
The icing on the cake for me was seeing examples of hand-fit dovetails from the main advocate of dovetail necks when they are removed for resets. Many of those dovetails are far less "perfect" than they would like you to believe. It's no wonder the heel / body fit shifts over time.
As Skar relates above, a undercut heel and hand lapping the heel edges allows the casual builder to easily produce a good fitting joint that locks together using simple bolt pressure that doesn't count on a specific amount of force. Since we're locking hardwood surfaces together there's no need to go all Mongo on the bolt tightness. If there's a worry about loosening of the joint you can always go with stacked Bellville washers to provide a calibrated and consistent amount of force.