A 2- or 4- flute end mill makes a fine trepanning tool on the lathe.
Trepanning of a square blank held on an expaning arbor through a smallish center hole leaves a square with a round hole, and a disc with the smallish hole. If what one wants is the disc, trepanning saves the wear, tear, and irritation of the interrupted cut, and save turning all those square points into chips.
I am trepanning an octagonal blank into a center disc and outer collar to hold a thin walled tapered part, soon.
I hold my 5/16 4-flute end mills in the cross slide with a boring bar adapter, a keyless chuck, straight shank adapter, and a sleeve. I've trepanned Masonite, acrylic, and polypropylene with this setup.
Align the collinear end teeth radially to the rotation center carefully so they will cut with correct rake and clearance. Alignment to the machine axis is less critical, except when cutting steel; the side flutes will burnish steel and harden it before they start cutting if they're not precisely aligned. This is a Bad Thing and can ruin the cutter. I know this will happen even though, as you read above, I haven't trepanned steel. It's one reason I haven't. In any other material, misalignment will only result in a little side cutting action during feeding.
Best,
Doug