The largest I've turned so far is small lengths of 2" OD 6061 and brass. I did turn some 3-on OD 6061 that was 12" long gripped by ~1/2-in in the 3J chuck and unsupported by a tailstock. That wasn't too bad and the time the work popped out of the chuck was actually pretty uneventful. I was turning at pretty slow speed though.