Design for manufacturing (DFM) strategies help companies to develop new products that are feasible to manufacture. In the early stages of design all engineering activities are initiated in computer aided systems. When the design is finished, the process of manufacturing and production planning begins. Issues often occur at this point because two teams, designers and manufacturers, have been working separately. The resulting question is: ‘how can Knowledge Engineering (KE) be used effectively to enhance manufacturability during early design?’ Even if the most complex geometrical product can be realized using today’s technologies such as rapid prototyping it is only true in unit production. In lot and mass production where CNC machines are used, complex geometry causes a number of difficulties. So it is important to investigate the project carefully in the early design stage from the point of view of whether it will be possible to manufacture.