Thanks, uffeiac. I'll check it out.I found this on another forum so don't take my word for it!!
Llink to discussion: http://www.harmonycentral.com/forum/forum/guitar/acapella-41/1104801-
I found out what is going on with the Hagstrom H-Expander. The hex screw in the end is NOT a normal truss rod adjuster.
In fact, it's a "set screw" that screws down agains the end of the rod that goes through the body of the H-Expander.
To adjust the neck you have to apply pressure against the middle of the neck (and have the strings completely loosened). THis will bow the H-expander and make the rod going through the middle also bowed - leaving a little extra room between the rod end and the set screw. Now you tighten the set screw to press against the rod.
When you relieve the pressure from the middle of the neck the H-Expander will be set in place and won't budge. This is NOT like the normal truss rod. And people who complain about the hex screw not turning are not doing the right thing.
The H-Expander has to be pre-bent to the amount of back bow you want prior to adjusting the set screw. If you just keep on turning the set screw and try to force it you are likely to strip it out. The good news is that if you do you can probably get a replacement and replace it since the set screw will come out if you completely unscrew it.