Here's another bit of 'souping up' I did on the Martin guitar. A little background is in order first.
The earliest Martin guitars had no neck reinforcement. Since virtually all of them were built for gut strings, tension on the neck wasn't an issue. With the popularity of steel strings beginning in the 1920s and with the advent of the 14-fret OM model, in 1934 Martin began putting a steel "T-rod" in its necks. The rod was 'T' shaped in cross section.
In the 1960s, Martin switched over from the T-rod to a more modern, square hollow rod. The hollow rod was lighter, and allegedly stronger than the old rod. However, a lot of people believe the necks are not as strong as the earlier ones. Finally, in 1985, Martin changed to the modern adjustable rod it uses to this day.
Since our project guitar is from 1971, it has the hollow neck rod. Knowing that carbon fiber rods were being used in some modern guitars, and knowing that Stew-Mac, LMI and others sell carbon rods, I wondered if I could slide a carbon fiber rod inside the Martin rod to add some strength.
I found I wasn't alone. Turns out Dan Erlewine had written a piece on the Stew-Mac site about doing this! Crazy!
So I pretty much followed his direction to the letter.
Slide the rod into the hollow rod in the guitar neck and mark it for length, then cut it.
I only know of carbon fiber from motor racing - if you follow Formula 1, you know it's used everywhere on F1 cars due to its strength and light weight.
(During this project, I kept thinking of David Hobbs ('Awbs') saying "that schamozzle's left a lot of carbon fiber shahhds all over the racetrack.")
The neck's actually in good shape - this may not have been necessary. But if there is an bow in the neck, this is a good idea to ensure the neck is straight and the rod will go in straight.
You also need a length of plastic binding that will go alongside the rod for a good fit.
See the rod (thick) and the piece of thin plastic binding alongside the epoxy bottle.
No one will ever see this repair once the guitar's back together, but I went with black binding and epoxy, just cause it seemed like the thing to do.
Pour about half of the epoxy into the rod.
You can clearly see the hollow rod in this picture.
Then fill the rod with epoxy. I found it made a little puddle at the top, and eventually drained down into the rod.
Between the epoxy and the binding, the carbon rod is pretty much in place. Forever.
Here's Dan Erlewine's writeup of the process.
The Complete Martin Guitar Restoration Saga
Repairing heel break
DIY chisel for bridge plate removal
DIY bridge plate removal iron, Pt.1
DIY bridge plate removal iron, Pt.2
Steam removal of bridge plate
Bridge plate removed
Tongue brace removal
Crack repair and brace scallop
New bridge plate Pt. 1
New bridge plate Pt. 2
Patching hole in top
Final fitting of top patch
Installing carbon fiber rod (This page)
Fingerboard crack repair, Pt. 1
Fingerboard crack repair, Pt. 2
DIY fret bender tool
Refretting Pt. 1
Refretting Pt. 2
Tuner shaft repair
Neck reset - dovetail fitting
Measuring neck set with DIY jig
Gluing the neck with hide glue
Fitting bridge pins
Making bone saddle
Making a buffalo horn nut