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Mostly to see if I can do it, I'm making a truss rod. It's pretty clear that unless one values one's time at near-zero, it's not an economically viable option. Commercial truss rods are cheap by comparison.

But it's coming along. I've got one end done. The other end awaits the arrival of a left-hand tap and die set.

There are a few different designs out there. The ones that I have had experience that failed all had one thing in common. That was the barrel nut was welded or silver soldered to the threads , This process most likely didn't have much process control , and the threaded rod snapped upon tightening the unit.
The design that I use now is like the Martin design where there is a cylinder that is welded to the back spine and the barrel nut is formed into the cylinder and it pulls or pushed on the spine to allow adjustment.

I am enjoying this and hope you post more. You will help many here . thank you

I got it finished. I'm not sure I'd trust it to stand up under load or not, but out it the open it works both ways quite readily. My apologies for the poor-quality picture, but it does show that it bows when tightened.

A simple rig to test it is to make a groove in a board to fit the rod clamp a board on the and test the unit. I think you may have a working unit.
Nice to see a metal head here

The truss rod looks as strong and better put together than the ones I use. Looks like a fun project.

The end blocks I think are fine. They have plenty of surface area that got brazed to the flat bar, and they're keyed in slots, which guarantees alignment and also increases the brazed surface area. I'm mostly worried about the rod snapping at the adjustment end. It's a 3/16" diameter rod, threaded 10-32 Left-Hand, and also drilled out #30 (0.1285") to accept the shank of a socket-head capscrew, the head of which then provides the means of adjustment. Between being drilled out, and threaded on the outside, there isn't much thickness left. The root diameter of a 10-32 thread is around 0.152". 0.152 - 0.129 = 0.023", or a wall thickness of around 0.0115". In theory. Add to that the fact that there is corrosive brazing flux trapped in the hole, and it's plenty to make one wonder about long-term reliability.

I like the idea of a test fixture...maybe I'll tr that. That won't tell how robust it will be five years from now though.