How do I rout a sharp inside corner?

Kitchen cupboard doors made from sheet material using cnc machines usually have sharp inside corners instead of the radius corners done with orthodox routers. Despite many years as a woodworker I have never seen any way of squaring the corners in a conventional workshop or factory. (except with a hammer and chisel)

How can I setup my homemade cnc router to do the same thing that the cnc kitchen manufactures do?

Regards
Bob Thomas