Variety of ways to get the bottom little stub/nub off of a piece depending on the wood. Sometimes I can use a thin parting tool and get a very small piece holding it on then a sharp chisel to clean it up. Sometimes the wood just isn't stable enough at that little spot to risk it breaking and coming off the lathe. Especially on hollow forms where the pith is the center and not that strong. I use a thick plastic card (an old car dealer drive out tag) with a notch cut in it to make it easier to use my cutoff saw to get rid of most of the nub. It's easier to then use a chisel for cleanup if there isn't as much material to deal with. I've tried without the card and invariably I will have a tooth from the saw rub on the bottom rim/foot of the piece or slip and cause a really nice deep scratch. This piece is Catalpa. Very soft and the pith was not strong enough to support using a tool any further.