One of the most useful handrail adjusting tools that I have is a large bench vise. It has four inch wide jaws and is perfectly square. Put wire in vise, bend with hands and finish with a hammer and I have a perfext 90 degree bend.
The vise is also good for straightening handrails I put 4" across the jaws and tighten. The rotate90 degrees (using existing bend) and tighten jaws again. Several repetitions give me a straight handrail.
Fortunately the vise is square enough that I can use it to press wheels on axles.
