Extension lines may be dotted, as explained in Mechanical Drawing, Part HI, or they may be fine, full lines, the latter method being illustrated in the series of pump plates in this paper. Dimension lines are also often made fine, full lines. If these lines are made full they should be made as fine as it is possible to draw them and still have them firm, clear lines. The same width should be used as for center lines.
Character in inked figures and letters is more difficult to attain than in pencil work. In the first place a pen suitable to the style of drawing is necessary. A civil engineer's fine mapping pen, which gives character to bis drawing, is not desirable in producing the bold character of a machine drawing. For the latter, choose a rather stiff, blunt pen which is not "scratchy," but runs smoothly, making a line of uniform width. A pen with a round, or ball-shaped nib, now on the market, answers the purpose well for ordinary details. A bold, free stroke should be made with the idea of producing a smooth, even line, finished at the first trial. The hesitating uncertainty of the beginner's hand produces a "shaky" letter, and going over a letter or figure twice or more to smooth it up usually makes it worse.
Fig. 124. Section Showing Varia-tions in Croeshatching.
Figures and letters which are broad in proportion to height are easier to make, and have more character. It should never for a moment be forgotten that uniform height and slope carefully followed will develop character and quickly lead to artistic excellence.
Foot and inch marks are often put after figures according to the common usage. In cases where feet and inches are expressed, thus: 3'-6", or 4'-0", they are, of course, absolutely necessary, and the dash between the figures must be very positively indicated. In cases of inch dimensions alone the marks may be put on if desired, but where there can be no doubt that inches, and not feet, are meant, the inch marks are not necessary.