Overview
ISO 522:1975, "Special tolerances for reamers", defines how to specify special dimensional tolerances for the cutting diameter of hand and machine reamers when a tighter accuracy grade than the standard stock grade (m6) is required. First published in 1975, this International Standard replaces ISO Recommendation R 522‑1966 and is intended to give a consistent method for relating reamer dimensions to the required hole tolerance (IT grade).
Key topics and technical requirements
- Purpose: Specifies limits for the diameter of the cutting portion of reamers to produce holes with a given tolerance class (IT).
- Applicability: Hand reamers and long-fluted machine reamers (ISO/R 236) and machine chucking reamers with parallel or Morse taper shanks (ISO/R 521) when a non‑standard stock grade tolerance is required.
- Main rules:
- The upper limit of the reamer diameter = maximum hole diameter minus 0.15 × IT.
- The lower limit of the reamer diameter = upper limit minus 0.35 × IT.
- Rounding:
- Values of 0.15 × IT and 0.35 × IT are rounded upwards to the nearest 0.001 mm (or 0.0001 in for inch sizes).
- For inch-size reamers, IT values are obtained by direct conversion from metric IT values.
- Practical note: Reamers are commonly manufactured to the stock grade m6, and hole size actually achieved depends on many factors (material, cutting angle, tool condition, mounting/operation, lubrication). ISO 522 therefore gives a recommended method to determine special reamer limits rather than guaranteeing hole size under all conditions.
- Examples (from the standard):
- For a 12 mm H7 hole (IT7 = 0.018 mm):
- 0.15 × IT = 0.0027 → rounded to 0.003 mm; upper reamer limit = 12.015 mm.
- 0.35 × IT = 0.0063 → rounded to 0.007 mm; lower reamer limit = 12.008 mm.
- For a 0.5 in H7 hole (IT7 = 0.0007 in): upper reamer limit 0.5006 in, lower limit 0.5003 in.
Applications and users
ISO 522 is useful for:
- Tool designers and manufacturers specifying reamer production tolerances.
- Machining and manufacturing engineers creating drawings and procurement specifications for reamers.
- Quality and inspection engineers verifying reamer diameters against required hole tolerances.
- Tooling suppliers and workshop machinists who must match reamers to required hole accuracy (e.g., H7 fits).
Practical use cases include producing precision holes for bearings, dowel fits, and assemblies where controlled hole size and surface finish are critical.
Related standards
- ISO/R 236 - Hand and machine reamers (referenced for reamer types)
- ISO/R 521 - Machine chucking reamers (referenced for shank types)
- General IT grade and limits/fits standards (metric‑to‑inch conversion noted in ISO 522)
Keywords: ISO 522, special tolerances for reamers, reamer tolerances, reamer diameter, IT grade, H7, m6, machining standards, reamer specification, dimensional tolerances.
