That shaft is rather hard and threading it can be difficult for a "first timer". Best that the machinist does it. Take your new prop hub with you when you go. Also, when you talk to him again, explain that the crankshaft is a "cantilevered" type and there is no way to chuck it in the lathe for threading. It has to be done with a threading die. That might convince him that the engine does not need to be disassembled.

Additional note: I have found studs for use in the prop hub to mount the propeller at Lowes, Home Depot, and Ace Hardware stores. Take your propeller and prop hub with you to make sure you get a stud with the correct size and threads, and long enough for a prop, large flat washer, and nut.

AV8TOR