Plate A shows such a preliminary outline drawing. It will be seen that this drawing is more or less rough. There is no detail and there are no dimensions except such as are determined by the designer's data and the known requirements as to over-all dimensions, such as length from face of coupling to end of outboard bearing, height from floor to center line of shaft, etc. No pains have been taken to make the drawing of value to the shopman, since it is used only in the drafting room. It gives the detail man a better idea of the whole machine than the data submitted by the designer. While the lines are put in without much regard to detail or accuracy, they convey the proper idea, and time spent in unessentials would be wasted on such a drawing.
The draftsman now has, in addition to the designing data, a sketch giving information to the eye as well as to the mind. He sees at once that a start must be made from this and, if he is a good draftsman, he knows that he must as far as possible work out completely each part as it is reached. He should avoid starting any part unless enough is already known to finish that part. This principle cannot always be followed, since some parts are interdependent and must be worked up together before they can be detailed individually.