Machine design is a complex undertaking, requiring many skills. Extensive relationhips need to be subdivied into a series of simple tasks. The complexity of the subject requires sequence in which ideas are introduced and iterated.
We first address the nature of design in general, and then mechanical engineering design in particular. Design is an iterative process with many iterative phases. Many resources exist to support the designer, including many sources of information and an abundance of computational design tools. The design engineers needs not only to develop competence in their field but must also cultivate a strong sense of responsibility and professional work ethic.
There are roles to be played by codes and standard, ever present economics, safety, and considerations of product liability. The survival of a mechanical component is often related through stress and strength. Matters of uncertainity are ever-present in engineering design and are typically addressed by the design and factor of safety either in form of a deterministic (absolute) or statistical sense. The latter statistical approach deals with a design's reliability and requires good statistical data.
In mechanical design, other considerations include dimensions and tolerances, units and calculations.