The rod is 36" fully threaded. I need to hacksaw it into two pieces.

Do you think I will ruin the threading with the cut, and I will not be able to screw on a nut.

Is there a technique ?

Hi oneill474, no I have hacksawed a threaded rod before and had no trouble using it afterwards. You will not ruin the thread.

I don't have power tools, but that old hacksaw sure comes in handy.

Tick

Yep, technique is everything.

Mark the cut. If I were doing this in a vise, I'd double nut in two places on one side of the cut. Then you can hold in a vise.

Easier way is to cut one side of a nut. It acts as a clamp.

Make your cut and then sand or file the end. Dremel, belt sander, sanding disk, whatever.

When you remove the nut it will cut the threads.

If it is something like 3/8 steel rod, it usually cuts just fine.

You can cut and sand afterwards. Jig saw works.

I cut it all the time and have seldom had a issue

I agree, no rocket science. I do the nuts on first, make the cut and then run the nuts off through the cut. That usually cleans any burrs enough to restart the nut.