Mechanical drawing plays a large part in directing the performance of all industrial operations. It is the guiding hand, so to speak, which directs the erector in the shipyard, the machinist in the shop, and the builder of bridges at the river. Therefore, a knowledge of the principles of science underlying its application is as important as a knowledge of the science of the trade.
In making a mechanical drawing, certain supplies are necessary. The first requisite is a pencil, properly made; the second, a paper of suitable quality for the work in hand; and the third, an eraser of just the right degree of hardness. With these simple yet important tools, together with a compass and ruler, the draftsman makes his working drawing. The tracing of the pencil-made drawing is the next step in the process. For the purpose of tracing, tracing cloth and paper are necessary, as well as a special kind of ink, called India ink. After a tracing has been completed, the making of the blue-print comprises the final step. A blue-print is used because if it is lost, another one can easily be made, whereas an original drawing can be made only at the cost of much time and money.