Assuming you’re going to cut a round design, earrings are a snap to cut. Once you’ve decided on the diameter, just free-wheel the quill and make both pieces the same size… cut and polish one and then put the other on the machine with the height of the mast the same. That will give you two identically sized, smooth girdles… I don’t facet the girdles on earrings, just polish them both.
Then just go ahead and cut ’em. They’ll come out exactly the same.
BTW: Quartz polishes great with CeOx.