ISO 2203:1973 PDF

Overview

ISO 2203:1973 specifies conventional representation practices for the toothed portions of gears used on technical drawings. The standard applies to individual (detail) drawings and assembly drawings such as gear pairs, worm gearing and chain wheels. Its purpose is to ensure uniform, clear depiction of gears across engineering documentation using a consistent projection method and simplified tooth representation.

Key principles include:

• A gear is normally shown as a solid part without explicitly drawn teeth (except in axial sections).
• The pitch surface is indicated by a thin long chain line (pitch circle or median pitch circle for worm wheels) even in concealed or sectional views.
• All illustrative figures in the standard use first-angle projection for uniformity (the principles can be applied equally in third-angle projection).

Key Topics

• Contours and edges: Represent gear contours and edges as if bounded by the tip surface in unsectioned views. In axial sections, show a spur-gear appearance with two diametrically opposed teeth unsectioned, even for non-spur gears or odd tooth counts.

• Pitch surface: Draw the pitch surface with a thin long chain line. In projections normal to the axis, use the pitch circle (external for bevel gears; median for worm wheels). In projections parallel to the axis, represent the apparent contour and extend the line beyond the gear contour on each side.

• Root surface and teeth: Generally omit root-surface lines on unsectioned views; show them in sectional views or when helpful. If one or two teeth must be shown (to define ends of a toothed portion or position relative to an axial plane), represent them as thick continuous lines. Indicate tooth direction (helical, double-helical, spiral) on the tooth-surface view using three thin continuous lines of the corresponding form.

• Assembly representation: Apply the same detail-drawing rules to assembly views. For bevel gear pairs shown parallel to the axis, extend the pitch-surface line to where the axes meet. In mesh, gears are not assumed to hide one another except when one physically conceals part of the other or when both are in axial section.

Applications

This standard is essential for:

• Engineering drawings of gear components and assemblies
• Manufacturing drawings where consistent gear depiction aids interpretation
• Design documentation for transmissions, worm drives and chain systems
• Technical publications and drawing templates used by engineering teams

Benefits include improved clarity, reduced ambiguity in interpretation, and consistent representation across suppliers and engineering teams.

Related Standards

While ISO 2203:1973 focuses on graphical representation, it complements other standards that define gear geometry, tooth profiles and tolerancing. When preparing drawings, reference ISO 2203 for depiction conventions alongside applicable standards for gear dimensions, materials and inspection criteria.

For practical use, follow the ISO 2203 rules for pitch-surface lines, projection choice and selective tooth depiction to produce clear, standardized technical drawings of gears and related components.