Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
We saw a jig/manual stretching gizmo at Vastex when we took their course. When we work with anything metal, we try to get it into a jig to weld, bend, cut, etc,, and find that has been a great way to keep items flat and square, or angled correctly. Might apply to Newman frames as well.