3 - ISO Drawing Rules

Abstract

This chapter provides information on the way to specify manufacturing requirements in an engineering drawing according to International Standards Organization (ISO) standards and discusses issues such as sizes, shapes, dimensions, tolerances, surface finishes, and assembly specifications. The ISO 128:1982 gives 10 line types that are defined as A to K (excluding the letter I) for covering line types and thickness. The ISO 128:1982 states that the thickness of a “thick” or “wide” line should be chosen according to the size and type of the drawing from the ranges 0–18, 0–25, 0–35, 0–5, 0–7, 1, 1–­4, and 2 mm. However, in a direct contradiction of this, ISO 128–24:1999 states that the thicknesses should be 0–25, 0–35, 0–5, 0–7, 1, 1–4, and 2 mm. Various ISO standards are concerned with dimensions, which come under the heading of the ISO 129 series. The basic standard is ISO 129:1985, but it has various parts. There are six ISO standards on lettering alone. The six parts of ISO 3098 refer to general requirements (part 0), the Latin alphabet (part 2), the Greek alphabet (part 3), diacritical marks (part 4), CAD lettering (part 5), and the cyrillic alphabet (part 6). Standard screw thread and threaded part dimensions are detailed in ISO 68-1 and ISO 6410; parts 1, 2, and 3 in 1993. ISO 15786:2001 is, however, concerned with the symbology and the abbreviations associated with holes. A leader line is a line referring to some form of the feature that could be a dimension, an object, or an outline. A leader line consists of two parts: type B line and the terminator. Various ISO standards are concerned with dimensioning. Colors are normally not used in engineering drawings. The term “draughtsman's license” refers to the freedom of a draughtsman to express the design in a drawing form, irrespective of the method for drawing (hand or on a CAD system).