I'm reasonably new to CNC. Have had no issues with setting up operations etc until now. Here's a picture showing simply the stock and in blue the surface I want to mill. When I do a 3d milling operation it happily cuts away at the circle first but then does the outside of the stock. Normally that would be fine but this time for s & g's I only want to mill this one face. I've tried every process I can think of as well as redefining the geometry in solidcam but it won't allow me to do that one surface.

Am I missing the big picture? Is there something I should have done during the cad process to make this easier?

Many thanks for any help
Raf