Let's kick this around. What about instead of 4 smaller threads, one big one. Imagine taking say a 2-1/4" shaft and wrapping two pieces of (guessing 1/4" X 1-1/4") steel around it using a rosebud. Experiment with paper to see what width gives you the advance to degree of turn ratio we want. Then take one of the pieces off the shaft. Drill through the remaining flat bar into the shaft, plug weld numerous close places and grind clean. Now we have a big fast screw. Next bore a block to the OD of shaft plus the flat bar. Insert the other bent flat bar we saved from wrapping the shaft, into the bored hole in the block and plug weld through holes drilled before insertion and clean up with a die grinder to make the nut.
Matt