Thanks Dave
That's the easy obvious way, but don't think it would work
Once it started twisting, it'll carry on twisting at the same spot and probably snap off
My idea is to grip the bar in the vice with 1" protruding and at 1/2" from the vice jaws, twist the bar with a home made square socket, made from 1/4" MS plate, through a repeatable angle
Then repeat by releasing only 1/2" at a time
I've made a start, using this method, but the choice of torsional bending angle, appears to be not enough
It should have worked out to be 1/2" pitch, but looks more like 3/4"
All great fun, all the same…….Will post a photo shortly
All the best…….Bob