The absence of a common approach for design and development of Web-based CAD/CAM systems is associated with increased risks and challenges. To overcome them and facilitate successful implementation of this kind of software within the commercial environment, a systematic approach is required that will ensure robustness, effectiveness, usability and ease of maintenance of these applications. This research establishes a methodology for creating Web-based CAD/CAM software systems, which will help develop complex Web-based CAD/CAM systems to industrial quality standards in a time and cost effective manner. The crucial parts of the methodology are a novel project development model facilitating architecture optimisation early in the project and a novel approach for planning based on time reserve management and task prioritisation.