Hi Ray M and other guys,
I located two very nice YouTube videos on this topic.
This one does not even require a thread cutting lathe or thread cutting skills.
It has the further advantage, for easy fabrication, and of enabling the use of standard threaded rod for the worm screw.
Keep in mind that there is a lot of sliding friction in any worm gear drive and especially when you use threaded rod or a home made worm. If you want, after assembly, put some lapping compound in the mechanism to smooth out the rough spots. Clean it VERY thoroughly afterwords before using it for you application - even to using soap and water.
A more elaborate fabrication video, but still fairly easy video is at
This has the advantage of having an Acme thread profile. It does require an Acme thread gauge to make a proper tool bit profile, a thread cutting lathe, a milling machine, and a spin fixture or dividing head.
This would be a thread profile of what is used in the automatic clutch feed mechanism of a industrial lathe like Logans and some South Bends. Note that this is NOT the same as using the thread cutting mechanism with a very fine feed gear setup like that used on an Atlas, some South Bend or similar non-clutch feed lathe. They use the lead screw and half nuts.
I am going to try the first one above just for fun. I have no application in mind except for "Show and tell" in the Mechanical Engineering lab I teach at the University where ME students become familiar with how things evolve from drawings to hardware.