First pic shows a pointed drill bit I used for gouging most of the waste. This bit's point was almost the valley profile needed. https://www.flickr.com/photos/43836144@N04/49585310742/in/dateposted-public /
Scroll left for two more pics relative to this next paragraph.
It took 2.5 hours to carve the remainder of the threads. The screw aspect tracked well within the threads, but the threads were not nearly deep enou gh. Today I deepened the threads (another 1.5 hours work) and still they a re not deep enough. It will take a good bit more time to get this half nut carved reasonably well.
I'll finish this half and reluctantly carve the other half, but I think I'l l stick to making wheel barrow handles. This thread carving is turning ou t to be quite a chore. I'll definitely further consult with the machinist.