When the number of different machines to be built does not exceed thirty or forty the letters of the alphabet may be very conveniently used; in the more frequent cases a single letter only being required. This will be readily seen from the scheme which follows, and is adaptable to a shop building machine tools in a moderate variety.

A, 12-in. Engine Lathe

B, 16-in. Engine Lathe

C, 20-in. Engine Lathe

D, 24-in. Engine Lathe

E, 30-in. Engine Lathe

F, 36-in. Engine Lathe

G, 45-in. Engine Lathe H, 60-in. Engine Lathe J, 24-in. Planer.

K, 30-in. Planer L, 36-in. Planer M, 48-in. Planer.

N, 60-in. Planer P, 16-in. Upright Drill Q, 24-in. Upright Drill R, 30-in. Upright Drill S, 40-in. Upright Drill T, 10-in. Shaper U, 16-in. Shaper V, 24-in. Shaper W, 10-in. Slotter Y, 15 -in. Slotter Z, 20-in. Slotter.

The letters I, O, and X are omitted for the reason that the letter I is so near in appearance to the figure 1, and the letter O to the cipher, that they are likely to cause confusion. The letter X is omitted as it is used to indicate changes in a pattern, as will be presently described. Other machines may be indicated by two letters instead of one, thus: AA, 9-inch bench lathe; BB, 12-inch hand lathe; CC, 20-inch special lathe; DD, 24-inch forming lathe. Or a 36-inch planer widened to 48-inch, instead of having its patterns and parts marked L, will have those made necessary by the change of width marked L-M, the last letter indicating 48 inches wide. In the same way a 36-inch lathe raised up to 45-inch swing may have the extra parts needed marked F-G. The hyphen is introduced to indicate that two machines are being considered in the designation. The letters of the alphabet having been exhausted in this manner, other combinatious may be resorted to, as AB, BC, etc., omitting the hyphen, as only one machine is meant to be referred to. This system will be found to have many advantages, not the least of which will be the ease with which these symbols are committed to memory.

In designing the parts of a machine the list is divided into sub-heads or groups of related parts. An engine lathe list will be divided into the bed, headstock, tailstock, carriage, rests, countershaft, etc., each of these headings including the principal piece mentioned, and all its related parts or appendages. In fixing the designation numbers to the various parts the bed would be 1, and the other parts following in regular order. When all the parts of this group are numbered a sufficient number of blank spaces are left for additions in this group. Then the next group is proceeded with in the same manner. The similar parts in several machines of the same class will receive like numbers, the distinctive letter symbol of the machine designating the individual part, pattern, or drawing thereof. For instance, the headstock of a 20-inch lathe may be designated C40, while that of a 36-inch lathe would be F40, and so on.

When a pattern or a part is altered the fact is indicated in red ink on the original drawing, and on the pattern a letter X is added to its former designation. Thus, the headstock of a 20-inch lathe when altered becomes C40X, each successive alteration adding another letter X to its designating mark, or in case of several alterations, one X, followed by a figure indicating the alteration, may be used. Thus, for the fourth alteration the mark would be C40X4. The red ink on the drawing gives the date when the change was made. Parts may be numbered in groups with reference to the materials of which they are composed. For instance, numbers 1 to 499 may be assigned to cast iron parts; 500 to 599 to malleable iron parts; 600 to 699 to steel casting parts; 700 to 799 to brass parts, and so on for forgings of wrought iron and steel and for the parts machined directly from the bar stock, etc., since every part made or purchased should have its distinctive number in order to carry out not only the drafting room system but that of the other departments of the works. In all drawings the part number should appear in a small circle to attract attention and to distinguish it from the dimension figures. It should be placed directly on the part where possible; otherwise at one side with an arrow.

Various schemes have been advocated for storing and filing drawings, tracings, and blueprints. It will be conceded, no doubt, that unmounted blueprints, drawings, and tracings should lie flat in drawers, and be so placed that the title at the lower right-hand corner may be readily accessible. The drawers should be constructed as shown in Fig. 181, with a strip A at the back, ¬ inch thick and 3 inches wide, to keep the back edges of the sheets in place and to prevent injury. There should be a separate drawer for the drawings of each machine, whose name and distinctive letter should be plainly marked on its front. A similar drawer for each machine holds the tracings, the two being kept in separate cases of drawers. For conveniently finding and replacing sheets the best method yet suggested seems to be that of separating them into groups of ten by interposing strawboard, properly indexed, as shown in Fig. 182. These sheets perform the double office of ready reference to the sheet wanted, and in the case of tracings they serve to keep them flat. The top sheet of strawboard bears the machine name and letter. This sheet should be an inch larger all around than the drawing or tracing, while the indexed sheets should be still an inch wider on the right-hand side so as to admit of ready indexing with plain figures.