WORKING DRAWINGS 134. A working drawing is one which is de signed for actual use in the shop or field. It is the drawing which goes out from the drafting room, and which conveys to the mechanic or builder instructions as to the machine, bridge, building, or other construction which is to be made. It must contain all the different views and dimensions necessary to enable the work man to go ahead and construct the thing required.
In order that the drawings may be readily understood by the mechanics, they must be made in accordance with customary drafting practice.
135. Detail Drawings; Assembly Drawings. For objects of more or less complicated struct ure—as buildings or machines—two kinds of drawings are necessary: the detail drawings, showing different parts separately; and the assembly drawings, showing the object as a whole.
If drawings are required of some object which is already constructed, in order that dup licates may be made, then preliminary drawings or sketches are first made. Dimensions and measurements are made directly from the object, and placed on the preliminary drawings or sketches. It is especially important that these sketches shall contain all necessary views and dimensions, as the object in question may be miles away from the drafting room, and the sketches are the draftsman's sole guide when making the final drawings.
For making these sketches, the draftsman should have a pad or notebook of cross-section paper, one or two triangles, a compass, a two foot rule, and a pair of calipers.
When an object is to be made for the first time, the design is first prepared by the engineer or designer from a consideration of the neces sary relations between the different parts and the requisite properties of the same. The head draftsman may then take the design, and work up the necessary details to a point where the drawings can be finished by the other draftsmen.
136. An important requirement which should be kept in view in making working drawings is clearness. The drawing should have but one meaning. To this end, enough views must be given, so that for the object represented no un certainty shall exist as to its shape and proportions.
These different views should be placed near enough together, so that they may be readily compared, but not so close that there will be any tendency to confusion. When certain necessary information cannot be conveyed by the drawing alone, explanatory notes must be given on the same or another sheet.
137. Kinds of Lines. Drawings are easier to read, and the meaning is made clearer, by the use of several kinds of lines, differing according to the purpose for which the line is to be used. The conventional types of lines for various pur poses are shown in Fig. 104. The full line and the dotted line should be of the same width; the center line, dimension line, and construction line should all be of the same width, and narrower than the first two; the extension line should be fine, and the shade line heavy.
For the broken lines, there is no standard length for the long or short dashes; but for a neat and properly made drawing, the short dashes of the so-called dotted line should be of equal length; and similarly, for all the broken lines, the like dashes when repeated should be of uniform length.
Many draftsmen are careless about their dash and dotted lines, with the result that their drawings are very likely to have a slovenly appearance.
138. Shade Lines. These are heavy lines, as shown in Fig. 104, applied to certain parts of the drawing. They are used principally for the sake of imparting character and relief to the figures. Shade lines are not essential, and in some drafting offices are dispensed with almost altogether. They do, however, give to a draw ing a certain finish which would otherwise be lacking, and in some cases materially assist in making clear the object represented.
How Shade Lines are Used. Theoretically, shade lines are the lines or edges which separate light from dark surfaces; practically they are applied to certain lines of the drawing according to a conventional system. Shade lines are ap plied only to lines which represent edges of an object; and, in the system most generally adopted, the right-hand and lower edges in both plan and elevation are the shaded lines.