I just turned an adapter in the lathe to fit my Hypertherm circle cutting  attachment.

Hello patriot, this is one that I made up a number of years ago. There are other concepts for these and it depends a lot on how you plan to use it as to which type might work best. As I said, this is one type. Good luck on your search/fabrication and best regards, Allan

Edit: I included the rotary table just in case you hadn't seen this sort of thing before. Essentially, I will center the punch mark for the circle that I am cutting out on my part with the "center" of the rotary table and spin the table while holding the torch stationary to assist with the circle cutting process.