How long carbon fiber rod for a Gibson A?

[Harmon Gladding]

In routing a 1/8 x 3/8 carbon fiber truss rod into a Gibson A, should I limit it to the neck, proper, or continue through the top and neck block?

[Marty Jacobson]

It's not necessary to continue the channel / rod through the neck joint and into the head block. Besides complicating future repairs on the neck joint, the amount of support it adds in that location is negligible -- at least assuming everything with your neck joint is ship-shape.
Maybe I shouldn't say negligible, but it's not enough to warrant the major headaches of removing it if any other neck or headblock issues arise 50 years from now.

[Paul Hostetter]

There are so many thousands of old Gibsons that clearly have no need for a CF rod, after 70 or more years. Why are you doing this?

[Pete Jenner]

Deleted. I didn't read the OP properly.

[Harmon Gladding]

Paul,
I see your point. It started with a separated fingerboard on my 1915 A, which I removed, refretted off the instrument, and straightened with some upward pressure at the ends and downward along the length.
I then started following Stewmac's trade secret no. 9, which talks about mandolin neck straightening and use of a carbon rod. But a closer look with a straightedge now shows the neck is only .001" low at midpoint. A straightedge held over the entire footprint of the fingerboard shows a .032" low spot at the neck/body joint. I am considering clamping the system straight and hot hide gluing the board.
Thanks