In producing working drawings the principles already laid down are constantly used, and the more they are at the ringer ends of the student the easier his work will become. The principles of projection must be thoroughly understood and fixed in the student's mind in order that he may devote himself with the greatest application to the actual detail of the drawing, and he must not be compelled at every step to turn back to find out how to make the simple projections.

Definition of Working Drawings. A working drawing is a drawing which completely instructs the workman, so that he is able actually to make in the shop the object which the drawing represents; in other words, a working drawing conveys to the mechanic all the information necessary to make the object. The student should constantly keep before him the idea that the workman must take a drawing, and, without any further instructions verbal or written, produce the object as the draftsman intended it to be made. The instruction supplied by the drawing should not only cover the form and size of the object, but also the kind of material of which it is to be made, the number of pieces desired, and the finish of its surfaces. A drawing, therefore, is a sort of abbreviated language, or shorthand method of conveying an amount of exact, detail information, which it would take many pages of manuscript to convey.

A second point to be noted in connection with a working drawing is that the workman has no time to puzzle over a mass of lines and figures more complicated than necessary. This means that special attention must be paid to making the drawing as simple as possible; all lines and figures which are unnecessary, beyond the point of conveying complete information, are hindrances rather than helps to the workman; moreover, it takes the draftsman's time to make these extra lines and figures, and thus the drawing becomes unnecessarily expensive. A good drawing, therefore, not only implies accuracy and completeness but also simplicity and directness.

Lines. The secret of a clear drawing, as far as the line work is concerned, lies not only in absolute uniformity in the making of the lines, but in choosing certain characteristic lines to convey different ideas. The most common kinds of lines used are shown in Fig. 1 and described below, and the purposes of their use are stated.

Full Lines. Full lines represent the portions of the object which are visible; they should be bold and clear, heavy on detail drawings, say ^" wide, and lighter on an assembled drawing.

lnvisible Lines. Invisible lines represent the hidden parts of the object; they consist of short dashes regularly spaced, the spaces being about \ the length of the dash; the dashes should never have a greater width than that of the full line, and usually should be slightly less. A drawing is much easier to read if the full lines force themselves on the eye, while the dotted lines, by their lighter character, are left in the background.

Center or Axis Lines. Center or axis lines consist of alternate long and short dashes, finer than the main lines of the drawing.