The problem I had doing it on my lathe was I started with a drill bit that was too big. I'm not sure removing seatposts matters enough for me to get a series of drill bits. I'm pretty sure if you sneak up on it, the seatpost will just come out with the last drill bit. The problem I had was that the chips were too big and were a lot stronger than the seat tube. Didn't help that I had a fancy butted seat tube.