A new machine is born because there is a real or imagined need for it. It evolves from someone’s conception of a device with which to accomplish a particular purpose. From the conception follows a study of the arrangement of the parts, the location and length of links (which may include a kinematic study of the linkage), the places for gears, bolts, springs, cams, and other elements of machines. With all ideas subject to change and improvement, several solutions may be and usually are found, the seemingly best one being chosen.
The actual practice of designing is applying a combination of scientific principles and a knowing judgment based on experience. It is seldom that a design problem has only one right answer, a situation that is often annoying to the beginner in machine design.
Engineering practice usually requires compromises. Competition may require a reluctant decision contrary to one’s best engineering judgment; production difficulties may force a change of design,etc.
A good designer needs many attributes, for example:
(1) A good background in strength of materials, so that the stress analyses are sound. The parts of the machine should have adequate strength and rigidity, or other characteristics as needed.
(2) A good acquaintance with the properties of materials used in machines.
(3) A specialized knowledge in various circumstances, such as the properties of materials in corrosive atmospheres, at very low (cryogenic) temperatures, or at relatively high temperatures.
(4) A knowledge of economics and comparative costs, because the best reason for the existence of engineers is that they save money for those who employ them. Anything that increases the cost should be justified by, for instance, an improvement in performance, the addition of an attractive feature, or greater durability.
(5) Inventiveness and the creative instinct, most important of all for maximum effectiveness. Creativeness may arise because an energetic mind is dissatisfied with something as it is and this mind is willing to act.
Of course, no one engineer is likely to have enough expert knowledge concerning the above attributes to make optimum decisions on every question. The larger organizations will have specialists to perform certain functions, and smaller ones can employ consultants. Nevertheless, the more any one engineer knows about all phases of design, the better. Design is an exacting profession, but highly fascinating when practiced against a broad background of knowledge.