I made a hinge rod today.  I was not able to completely straighten the hinge rod in the foot joint in my project flute.  It had been mangled a little.  The keys were all bend, the posts were out of line, and a solder joint on one of the ribs was broken.  After fixing the solder joint, and straightening keys and posts I decided I needed an new hinge rod because the kink in the original one would not come out.
I started with a piece of steel drill rod that was the same size as my original hinge rod.  I filed down the part that I was going to thread to the correct size, and then ran a die on to it.  Then I checked the fit on the keys and marked where to cut each end.  I beveled my threaded end, and cut a notch in the other end for a screw driver.  It was very successful!