ISO 494:2017

Overview

ISO 494:2017 - Cylindrical shank twist drills (Long series) specifies the dimensional requirements for cylindrical‑shank twist drills with working lengths in the long series. The standard defines geometrical dimensions and length rules in millimetres, provides tables of nominal sizes and diameter‑step length ranges, and includes an informative Annex mapping this document’s designations to the ISO 13399 cutting‑tool data model.

Key topics and technical requirements

• Scope: Dimensions apply only to cylindrical shank twist drills in the long series; jobber, stub and Morse taper shanks are covered by ISO 235.
• Units and tolerances: All dimensions and tolerances are expressed in millimetres.
• Dimensional tables: Table 1 gives nominal drill diameters, overall lengths and flute (cutting) lengths; Table 2 sets lengths as functions of diameter ranges (diameter steps).
• Length tolerance guidance: Lengths l1 and l2 may vary within the min/max values corresponding to adjacent diameter steps (example: for d = 4 mm, one listed nominal shows l1 = 78 mm may vary between 73 and 82 mm).
• Cutting length: Cutting (flute) length is at the manufacturer’s discretion, unless otherwise specified by purchaser.
• Shank details: Drills are specified to be manufactured without tenon drive and are right‑hand cutting unless specified otherwise.
• Data mapping: Annex A relates ISO 494 symbols (d, l1, l2, etc.) to preferred symbols in the ISO 13399 series for digital tool representation.

Applications and who uses this standard

ISO 494:2017 is intended for:

• Drill and cutting‑tool manufacturers - to design and produce long‑series cylindrical shank twist drills to consistent dimensions.
• Purchasing and specification engineers - to create unambiguous procurement specifications and ensure interchangeability.
• Machine shops and production managers - to select appropriate drill lengths and ensure tooling compatibility.
• CAD/CAM and tool‑data managers - to map product dimensions into tool‑data systems (via ISO 13399 correspondence).
• Quality and inspection teams - to verify drill geometry and length tolerances against standardized tables.

Related standards

• ISO 235 - Parallel shank jobber and stub series drills and Morse taper shank drills (complements ISO 494 for other shank/length types).
• ISO 13399 - Cutting tool data representation (Annex A provides symbol mapping).

Keywords: ISO 494:2017, cylindrical shank twist drills, long series, drill dimensions, cutting length, shank specifications, ISO 13399, tool standards, machining, drill bit dimensions.