bobcad-maxnc

Gentlemen,
I have been lurking out of sight for a few days trying to make sence of some
of the material posted. By that I mean I am a beginner in CNC with a Maxnc
conversion to my Sherline mill. Now the problem I hope you might help me
with; How do I tell Bobcad that the part I want machined is thicker than
one pass of the tool? When I do the recommended method in the manual it
seems to make only two passes the return to start. I know it can be done
but can't figure how?
PJH