New to Cad/Cam trying to draw in Vector...please help

I am trying to make a sign out of 1/4 in aluminum plate. I want it
to say BED 1 1.75" high letters. I don't want any pocketing, I want
the outline cut all the way through. Its easy enough to draw the
letters out to appropriate size, but how can I tell it the z depth
and how much to take off per pass. I want say 4 passes to get the
total depth of 1/4...SOmebody point me in the right direction.