Linework and lettering

This chapter presents some suggestions on linework and lettering used in engineering drawing. Two thicknesses of line are recommended for manual and computer aided design (CAD) drawings, where the wide line and narrow line are in the ratio of 2:1. Line thicknesses of 0.7 and 0.35 are generally used, which give good quality, black, dense and contrasting lines. All chain lines should start and finish with a long dash, and when center points are defined, the chain lines should cross each another at solid portions of the line. Center lines should not extend through the spaces between views and should never terminate at another line on the drawing, and the arcs should meet straight lines at tangency points. Lettering may be vertical or slanted, according to the style used by the draughtsman, where the aim is to produce clear and unambiguous letters, numbers, and symbols. Single stroke characters devoid of serifs and embellishments should be used and all strokes should be of consistent density. All drawing notes and dimensions should remain legible on reduced size copies and on the screens of microfilm viewers. On parts lists or where information is tabulated, the letters or numerals should not be allowed to touch the spacing lines. When lower case letters are used, they should be proportioned so that the body height will be approximately 0.6 times the height of a capital letter. The stroke thickness should be approximately 0.1 times the character height and the clear space between characters should be about 0.7 mm for 2.5 mm capitals and other sizes in proportion.