Fixed Neck Reinforcement – Preparation:
When my father made guitars 35 years ago, he always used fixed reinforcement for their necks and never an adjustable rod. I guess his philophosy was if it was good enough for a Martin it was good enough for him. While that may not be the best of reasons why you would do that, you have to admit, Martin has been very successful with their guitars. But, there have also been a lot of neck resets on Martin Guitars over the life of the company.
I still have one of my fathers guitars that I play regularly with the fixed reinforcement and the neck is still as straight, and in adjustment as when he make it – that is after 40 years. He was a very inventave type of soul, and had a lot of good ideas. While I now use a two-way adjustment truss in most of my guitars, I have made a great many guitars with fixed reinforcement.
Here Are Some of His Discoveries:
Use at least a three piece neck when laminating your wood.
Make sure you select vertical grain wood for the neck.
Glue the neck blank so as to have the wood grains work against each other for greater strength. Read up on the above 3 items in the Article on Guitar Neck Laminating.
For the neck reinforcement use Aircraft Aluminum for the best strength to weight ratio.
Use Aircraft Aluminum restraining pieces. (These are optional if you file ribs into the side of your reinforcement bar)
Glue everything together with epoxy glue.
About The Aluminum Reinforcement:
Aircraft Aluminum if tuff stuff. It is actually an aluminum that goes through a tempering process and really resists bending. It is easily cut on a band saw with a metal cutting blade, and it does not add so much weight to the neck that it places the guitar ‘out-of-balance’ or neck heavy.
The Aluminum restraining pieces are placed perpendicular to the reinforcement bar at each end – again this is a measure to prevent movement of the bar/neck combination. I have found that if the aluminum bar has cuts about 2″ along the length of the bar on each side, there is no need for the end restraints. The cuts should be about 1/16″ deep and cut perpendicular to the length of the bar.
Both the reinforcement bar and the restraints should be made a deep as possible without compromising the neck. This means if your neck tapers slightly from nut to body, the bar should follow the same taper. Also the restraining pieces should be shaped to follow the contour of the neck curve.
Pros and Cons of Fixed Reinforcement In The Neck:
I still make guitars this way and feel perfectly fine in doing so. Although you do not save any time installing a fixed reinforcement in the neck, it does give you a much more solid neck – unless you have a condition like the one explained below.
If the guitar will be subjected to extreme changes in temperature and/or humidity, the fixed reinforcement will probably give you more problems. The reason for this is as the wood neck adjusts to the atmospheric change the aluminum does not. The manner in which the bar is restrained will resist this structural movement to a great degree, but at some point the forces of nature will persist.
I found this to be true when I move to Hawaii for three years. I took one of my fixed neck guitars along with me and when I moved back to the mainland I found that the action of the strings had changed ever so slightly – about .5 to .75 mm. Not that much, but enough to turn a really easy-playing guitar into one that was not so easy to play. This guitar had a rock stable neck for decades prior to that move.
If you look at the diagram at the beginning of this article, this is a neck section at the 6th fret. This is a excerpt from our Guitar Plans, stripped of notes. Notice the aluminum bar in the center of the neck (shaded). Also note that dashed curved line that indicates the restraining pieces in the neck.
In the following article I will go through the installation process for a fixed reinforcement.