Overview
ISO 8830:1991 specifies technical requirements for high‑speed steel (HSS) machine taps with ground threads. The standard covers material and hardness of the threaded portion and shank, cutting geometry (flute and rake angles, chamfer/point), circular run‑out tolerances, and marking. It applies to standard taps manufactured in accordance with ISO 529, ISO 2283, ISO 2284 and ISO 2857 and may be used by agreement for non‑standard taps.
Key topics and requirements
- Material and designation
- Uses HSS grades referenced from ISO 11054; steel code must be marked on the tap.
- Hardness requirements
- Minimum hardness of the threaded portion is specified by nominal tap diameter. Representative values in the standard include:
- Small diameters: ~750 HV (≈61 HRC)
- Medium diameters: ~780 HV (≈62 HRC)
- Larger diameters: ~820 HV (≈63 HRC)
- Shank and square hardness: not less than 30 HRC, regardless of diameter or construction.
- Cutting geometry
- Defines helical flute angle categories (slow, medium, fast) with ranges (approximately 10°–20°, 20°–40°, >40°) and requires selection from Renard series leads.
- Rake angle is measured in a plane normal to the tap at the first full thread after the chamfer.
- Chamfer/point geometry and number of threads on the chamfer lead are specified by flute type (see table in the standard).
- The standard provides a formula to calculate the point diameter (d3max) from nominal diameter, chamfer length and pitch.
- Run‑out tolerances
- Circular run‑out tolerances (t1, t2, t3) are specified relative to nominal diameter and are checked at defined locations when the tap is mounted between centres.
- Marking
- Required marking includes: thread designation, tolerance grade, HSS code, left‑hand thread identifier (if applicable), and manufacturer’s name or trademark.
Applications and users
- Intended for tap manufacturers, tooling designers, quality inspectors, and procurement/specification engineers who need consistent, verifiable quality for HSS machine taps with ground threads.
- Useful for production machining, OEM supply chains, toolroom standards, and quality control procedures where repeatable thread form, hardness and run‑out are critical (e.g., automotive, aerospace, precision engineering).
Related standards
- ISO 529 - Short machine taps and hand taps
- ISO 2283 - Long shank machine taps
- ISO 2284 - Hand taps for pipe threads (dimensions & marking)
- ISO 2857 - Ground thread taps for ISO metric threads (manufacturing tolerances)
- ISO 11054 - Designation of high‑speed steel groups
- ISO 5967 - Taps and thread cutting nomenclature
Keywords: ISO 8830:1991, high‑speed steel machine taps, ground threads, technical specifications, hardness, cutting geometry, run‑out tolerances, tap marking, ISO 529.
