problem milling a complete band on the rotary table

I am having trouble cutting a complete band with my rotary table. Let's
say I try to cut a wedding band, the item will not travel the full 360
degrees.

The band will look like a letter C. The area it does not cut can be
anywhere from 5-8mm wide....

I am using a microproto mill with a sherline rotary table and DOS based
control software.

Can anyone offer a solution?