When a designer has. determined upon the action, position, form and material of each part of a machine, his ideas are sent to the drawing room in one or more sketches. From these an assembled drawing is made of the whole machine, to a definite scale, and by aid of the sketches and the assembled drawing, detail drawings are made in larger scale, convenient for showing the details of each part and for recording the dimensions.

In the design of a ship, bridge, structure or machine of any kind, the kind and quality of materials to be used must be determined by the designer, who must also determine the size and shape of each part with a view to giving it the required strength.