{"id":2513,"date":"2026-09-24T18:03:46","date_gmt":"2026-09-24T10:03:46","guid":{"rendered":"https:\/\/www.jccncmachining.com\/?p=2513"},"modified":"2026-09-22T11:16:41","modified_gmt":"2026-09-22T03:16:41","slug":"iso-21920-surface-texture-symbols","status":"publish","type":"post","link":"https:\/\/www.jccncmachining.com\/ko\/blog\/iso-21920-surface-texture-symbols\/","title":{"rendered":"\uc544\uc9c1\ub3c4 ISO 1302 \ubc29\uc2dd\uc73c\ub85c \ud45c\uba74 \uac70\uce60\uae30 \uae30\ud638\ub97c \uc77d\uace0 \uacc4\uc2ed\ub2c8\uae4c?"},"content":{"rendered":"

<\/p>\n

A surface-texture symbol is not shorthand for \u201cmake it smooth.\u201d It defines how a surface should be specified and evaluated: the parameter, limit, filter or nesting index, evaluation length, manufacturing requirement, and lay may all affect acceptance. ISO 21920-1:2021 now governs indication of profile surface texture in technical product documentation, so copying an old ISO 1302 note into a new CNC drawing can preserve outdated or incomplete assumptions.<\/p>\n

The engineering objective is not to modernize symbols for appearance. It is to ensure that design, machining, and inspection use the same specification. A lone \u201cRa 0.8\u201d may be familiar, yet still leave enough uncertainty for two instruments or suppliers to report different results.<\/p>\n

Decode the callout in a fixed order<\/h2>\n

\"callout-decoding\"\nWhen a surface requirement arrives, do not jump directly to a machining operation. Read the callout from its governing standard outward:\n\n\n

    \n
  1. Confirm the standard and edition referenced by the drawing.<\/li>\n
  2. Identify whether material removal is required, permitted, or prohibited.<\/li>\n
  3. Read the texture parameter and upper, lower, or acceptance limit.<\/li>\n
  4. Confirm the filter or nesting index and evaluation conditions.<\/li>\n
  5. Check lay direction, machining allowance, process restriction, and the extent of the controlled surface.<\/li>\n
  6. Agree where and in which direction the surface will be measured.<\/li>\n<\/ol>\n

    This is a specific branch of the site\u2019s broader CNC \uac00\uacf5 \ud45c\uc900<\/a> topic. It does not replace the drawing\u2019s general tolerances, geometry controls, or finish\/coating specification.<\/p>\n

    What changed from ISO 1302 to ISO 21920?<\/h2>\n

    \"iso-standard-migration\"\nISO 1302 remains common on legacy drawings and in company templates, but ISO 21920 reorganized profile surface-texture specification, measurement, and parameter definitions into a newer series. ISO 21920-1 covers indication on technical product documentation; Parts 2 and 3 address terms, definitions, parameters, and specification operators.\n\nThe migration is not merely a new symbol shape. It asks drawing authors to define the specification with enough measurement context to obtain repeatable decisions. ISO\u2019s official entry for ISO 21920-1:2021<\/a> states that it specifies rules for indicating surface texture by profile methods using graphical symbols.<\/p>\n\n\n\n\n\n\n\n\n
    Legacy-drawing risk<\/th>\nMigration action<\/th>\n<\/tr>\n<\/thead>\n
    Title block names no surface-texture standard<\/td>\nState the governing standard and edition<\/td>\n<\/tr>\n
    Only an Ra number is shown<\/td>\nReview parameter, limit, filter, evaluation, and function<\/td>\n<\/tr>\n
    Old company symbol is copied without explanation<\/td>\nTranslate its intended requirement, not its appearance<\/td>\n<\/tr>\n
    Supplier measures with default instrument settings<\/td>\nAgree settings and measurement direction before production<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    Ra alone cannot describe how a surface will function<\/h2>\n

    Ra is an arithmetic mean of profile deviations over the evaluated length. It compresses complex topography into one number. Two surfaces can share the same Ra yet differ in peak shape, valley depth, spacing, waviness, lay, scratches, and ability to retain lubricant or seal against a gasket.<\/p>\n

    Parameter selection should follow the failure mode. A sealing face may be sensitive to directional leakage paths and isolated valleys. A sliding surface may depend on peak behavior and lubricant retention. A cosmetic face may pass a roughness reading but fail because of tool witness marks or inconsistent brushing.<\/p>\n

    The article CNC surface roughness<\/a> explores the relationship among Ra, function, machining, and cost. This page focuses on turning that engineering intent into a modern drawing indication.<\/p>\n

    Filtering and evaluation settings can change the result<\/h2>\n

    \"filtering-evaluation\"\nA stylus trace contains features at different spatial scales. Form, waviness, and roughness are separated through defined processing. If the designer and inspector use different filters, nesting indices, evaluation lengths, or end-treatment rules, their reported values can differ even on the same physical surface.\n\nBefore approving the drawing, answer these questions:\n\n\n