Overview
ISO 17485:2006 - "Bevel gears - ISO system of accuracy" defines a unified classification system for the geometrical accuracy of unassembled bevel gears, hypoid gears, and gear pairs. The standard establishes terminology, the structure of an accuracy grade system and allowable tolerance values (by equations), and guidance on measurement practice (with measuring methods referenced in Clause 6 and supporting annexes). It defines ten accuracy grades (numbered 2 to 11, decreasing in precision) to enable clear specification and communication between gear manufacturers and buyers.
Key topics and technical requirements
- Accuracy grades and tolerances: Ten grades (2–11). Tolerances are given by equations (not fixed tables) and example values/graphs appear in Annex A. Tolerance ranges are valid for typical geometries (mean normal module, tooth count, tolerance diameter ranges specified in the standard).
- Terms, definitions and symbols: Precise definitions for gear accuracy terms such as index deviation, single pitch deviation, total cumulative pitch deviation, runout deviation, single‑flank composite deviation, transmission error, mean normal module, and tolerance diameter.
- Tolerance diameter and measuring directions: Definition of the tolerance diameter location and the prescribed measurement directions for pitch and composite deviations.
- Tolerance equations and step factors: Formulae for calculating allowable deviations per accuracy grade, with rules for step factors and rounding (Clause 5).
- Measurement and inspection: Clause 6 covers methods of measurement, recommended control methods, data filtering, and tooth contact pattern inspections. Annex B describes single‑flank composite measuring methods; other annexes address small‑module gears and interpretation of composite data.
Practical applications and users
ISO 17485:2006 is intended for:
- Gear manufacturers specifying and producing bevel and hypoid gears to agreed accuracy classes.
- Quality/inspection laboratories performing measurement, data filtering, and conformity checks for unassembled gears.
- Purchasing/specification engineers creating procurement tolerances and acceptance criteria.
- Maintenance and reverse‑engineering teams verifying gear geometrical conformity.
Practical notes:
- The standard applies only to unassembled (loose) gears and excludes enclosed gear units (reducers, gear motors, etc.) and does not include gear design guidance.
- Users are cautioned not to assume a direct correlation between the unassembled tolerance class and assembled gear performance without application‑specific experience.
Related standards
- ISO 1122‑1 - Vocabulary of gear terms (geometry)
- ISO 23509 - Bevel and hypoid gear geometry
- ISO/TR 10064‑6 - Inspection practice and measuring methods for bevel gears (companion technical report)
- ISO 1328 series - Cylindrical gear accuracy (useful for comparison)
Keywords: ISO 17485:2006, bevel gears, hypoid gears, gear accuracy grades, tolerances, tolerance diameter, single‑flank composite deviation, gear inspection, measuring methods, mean normal module.