ISO 21771-1-2024 PDF

Full title and description

St ISO 21771-1-2024 — Cylindrical involute gears and gear pairs — Part 1: Concepts and geometry. This part establishes the geometric concepts, parameters and related terminology for cylindrical gears with involute (helicoid) tooth flanks, includes flank modifications, and sets out the concepts for involute cylindrical gear pairs with parallel or crossed axes and a constant gear ratio.

Abstract

This document specifies the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks, including flank modifications; the formulae apply to all pressure angles. It also covers concepts and parameters for involute cylindrical gear pairs with parallel or crossed axes and a constant gear ratio, where gear and mating gear share the same basic rack tooth profile.

General information

• Status: Published.
• Publication date: 24 October 2024 (ISO publication: 2024-10; commercial records list 24 October 2024).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 21.200 (Gears).
• Edition / version: Edition 1 (2024).
• Number of pages: 159.

Scope

The standard defines geometric concepts, parameters and formulae used to describe cylindrical involute gears (spur and helical forms with involute helicoid tooth flanks) and their meshing behaviour. It includes definitions and notations for tooth geometry, flank modifications and measurement reference geometry, and applies to gear pairs with parallel or crossed axes having a constant gear ratio. The specification is intended to be generic across sizes and manufacturing methods and is applicable for all pressure angles.

Key topics and requirements

• Definitions and notation for cylindrical involute gear geometry (tooth form, helix, pressure angle, basic rack).
• Geometric parameters and formulae for involute helicoid tooth flanks and flank modifications.
• Application to gear pairs with parallel or crossed axes and constant gear ratio (matching basic rack profiles).
• Reference geometry for measurement and specification of tooth form and space.
• Compatibility with existing ISO gear geometry practice — replaces and updates the withdrawn ISO 21771:2007 concepts by extending into a multipart series.

Typical use and users

Engineers and designers of gears and gearboxes, manufacturing engineers, metrology and testing laboratories, standards committees, technical authors, procurement specialists specifying gear geometry, and academic researchers use this part as the foundational reference for defining geometry, communicating design intent, and establishing measurement references for cylindrical involute gears.

Related standards

This publication is part of a multipart ISO series on cylindrical involute gears. It replaces the earlier ISO 21771:2007 (withdrawn) and is complemented by further parts addressing calculation and measurement (for example ISO 21771-2 covering tooth thickness and backlash calculations, published subsequently as part 2). Work on revisions and committee drafts (ISO/DIS or ISO/CD documents) for related or follow-on parts has been recorded by the ISO technical committee.

Keywords

cylindrical gears, involute, helicoid tooth flanks, gear pair, gear geometry, flank modification, pressure angle, basic rack, tooth thickness, backlash, ICS 21.200.

FAQ

Q: What is this standard?

A: ISO 21771-1:2024 (St ISO 21771-1-2024) is Part 1 of a multipart ISO standard that defines concepts and geometry for cylindrical involute gears and gear pairs.

Q: What does it cover?

A: It covers geometric concepts, parameters and formulae for involute (including helicoid) tooth flanks, flank modifications, and the conceptual framework for cylindrical gear pairs with parallel or crossed axes and constant gear ratio. The formulae are given for all pressure angles.

Q: Who typically uses it?

A: Gear designers, gearbox manufacturers, metrology and test laboratories, standards developers, procurement/specification writers and researchers use it as the authoritative reference for gear geometry definitions and measurement reference conventions.

Q: Is it current or superseded?

A: ISO 21771-1:2024 is the current published Part 1 (published in October 2024) and supersedes the earlier ISO 21771:2007, which was withdrawn. Further related parts and revisions are under development as part of the ISO 21771 series.

Q: Is it part of a series?

A: Yes — ISO 21771 has been restructured into a multipart series. Part 1 covers concepts and geometry; subsequent parts (such as Part 2) address calculation and measurement topics (tooth thickness, backlash, etc.). Additional DIS/CD activity for related parts is recorded under the ISO technical committee for gears.

Q: What are the key keywords?

A: Cylindrical involute, helicoid tooth flank, gear geometry, flank modification, basic rack, tooth thickness, backlash, gear pair, pressure angle.