Excess material

Perhaps I did not express my question properly.

Let's say I want to cut a half cylinder shape into a block of
material. I draw it, define the contour and profile and Dolphin
generates the Gcode to mill out that shape. The problem for me is
that the tool path, if moving axially, will take succeedingly deeper
cuts as it progresses from one end of the cylinder to the other and
around the circumferance; if cutting radially then the cutter will
dive into the material deeper and deeper, then raise out of the
material as the tool tip moves in a down and over and up and out
path as it tries to cut the circumferancial profile.

My one thought for the inverse is to treat the part as an island and
mill away the excess material surrounding the desired part. As far
as I have learned in Dolphin so far there is no place to define the
raw material block that the part is to be cut from and I have found
no place to define the limits of the machine envelop. At this point
I can only assume that it is my responcibility to check the code for
possible overruns and that the limit switches ( which I don't have
on my Sherline) guard against the program trying to drive the tables
into downtown Seattle.

I mentioned this to the vector programmer (sorry, don't recall his
name)at the Southgate show and he was kind enough to very briefly
explain some parts of it. The bustle and many spectators made it
very difficult to retain much of this info however. It had something
to do with having the gcode repeatedly cut the shape at deeper
settings or at deeper Z settings. It's a little fuzzy at this point.
Thanks, PJH