How would i turn the bottom of a bowl?

There is a trick if you cant chuck the open end of your bowl into the chuck. drill a 2-4" diameter hole into a 2x8 cut to 8"long. Then let the chuck grab in this hole same as you do for a bowl. Now on the backside of the 2x turn it flat but leave a tenon sticking out in the middle big enough and long enough to chuck into your lathe. Then take it off of the lathe and glue a piece of thick cardboard onto the side with the hole. Not the corrugated kind with air spaces but the stiff solid kind like the back cover on a legal pad. Then glue the open top of the bowl to the cardboard being very careful to center it over the hole that you drilled on the other side. Then chuck the tenon to the lathe and turn the bottom of the bowl and then carefully tap a chisel into the joint where the bowl was glued to the cardboard until it pops off and just sand down and finish the lip of the bowl where the glue was. Second suggestion is cover the flat plate with the tenon with cork or rubber and then center the lip of the bowl on that rubber/cork surface and slide the tail stock up to the bottom of the bowl and then turn it to what you want. Then just sand off that tiny little part that was blocked from turning by the tail stock. Good Luck.