This paper explains the concepts of feature-based process plans as
developed in the Alpha_1 Computer Aided Design and Manufacturing
research software system. Our approach uses explicit feature-based
manufacturing process plan models as a basis for automatic high-quality
CNC machining program generation, including tool selection and feed and
speed computation and tool path construction, as well as generation of
tooling setup instructions for machine operators. The manufacturing
algorithms of one Alpha_1 feature type, ``general sculptured volumes'',
is used as a high-level feature example.  A complete process plan
example spanning the range of features is described. Finally, we
indicate some open areas for future work.