Nuff said:

A little closer view showing, left to right, saw-kerf layout lines, half-carved threads, finished threads:

Two hours later…
Here’s a pic of the screw and nut with all the threads cut:

In the background is the big tap I made to cut threads in the nut. I have fitted the screw’s threads to those of the nut for about half its length. If the screw appears bowed to you that’s because it is! Somewhere between turning the screw blank and chopping the threads it developed a slight bow…hope it doesn’t affect function.