I'm restoring my 1971 Martin D-35. I already replaced the 1/4" braces with 5/16" scalloped (due to too much bellying) and the large RW bridgeplate with a smaller maple one. Now that the back is glued back on, I need to do a neck reset. While I'm doing that, I thought I might stiffen up the neck a little. The relief goes from dead flat unstrung to .016" when strung up. A recent newsletter article from StewMac talks about inserting a carbon fiber rod inside the square-tube, non-adjustable truss rod to help stiffen up the neck. Does anybody have any experience with this technique?
I'm most concerned with relief. They say I can dial in whatever relief I like, glue the carbon fiber rod in and it will maintain that shape and relief. But I'm wondering what happens when I string it up? Will the string tension cause significant additional relief ? If so, how much can I expect? If it's only another .001-.002", I can allow for that when I set the relief statically.
Any help would be appreciated, especially from Frank ! Thanks