They actually are not
One of these steelies failed at the neck.
Out of a second pair of Ti drives, both failed at the neck.
I just installed the third set (2nd Ti set) and we'll see...
There needs to be torsion to soak up shock loads, there is no torsion in these, being a tube, and they will always fail eventually at the thinnest point. Which was my initial concern, and was justified obviously.
I had failures both with a diff, and a spool.
Did give me some experience working with titanium at least. Most unusual stuff, drilling to make the tube end was a huge pain. Not sure what grade I had because it was given to me, but it acted like 3 different metals. It files very easily, almost like aluminum, but it machines like high carbon steel. Drilling produces intense heat, far more than any material I've worked with.
Over the course of making 3 sets I determined that about .002"- .0025" interference fit is needed to secure the large pin (dogbone end). The first set of steel drives I tapped the end for a 3mm setscrew, not knowing the proper amount of pressfit I wanted a way to secure the pin. Those were made to be only about .0005 pressfit, not nearly enough and they did loosen. So the neck being hollow on the first pair with the relief drilled ended up being weak. One steel drive survives, but it is rather rusty. I think after this it will be back to either regular bones or possibly making some bones. But the tube CVD I think would be an excellent way to do custom length centerdrives, but for outdrives bones are still the best way to go.