When making a recess or tenon on the bottom of a bowl, the tail stock usually needs to be removed to allow access to the bottom of the object, but it is possible to make a tool that can be used for this purpose and you can retain the tail stock support.

This tool can be made from an old skew that is too short.  A  1/2" square skew is preferred.  Grind off the bevel points of the skew and grind the flat at about a 45° angle.  The recess is cut using the notch in the bottom of the skew.  Match the angle of your dove tail jaws.  Then cut the upper angle to match the tenon angle of your jaws.  A negative rake can be ground into the top surface of the tool if desired.

The diagram below is looking down at the top surface of the tool.  Set the tool rest so you are cutting just below center with the tool held horizontally.