📏 Surface roughness measurement (Ra, Rz)

Automotive PN-EN ISO 4287

Overview

STATUS (as of 06.11.2026). PN-EN ISO 4287:1999 — Polish version, published on 16.11.1999, which implemented EN ISO 4287:1998 and ISO 4287:1997 [IDT] — was WITHDRAWN on 21.06.2022 and replaced by PN-EN ISO 21920-2:2022-06 (English version). ISO 4287:1997 was withdrawn and ISO 21920-2:2021 was published on 20.12.2021; on the same day ISO 4288:1996 was withdrawn and replaced by ISO 21920-3:2021. The description below gives the content of ISO 4287 from the available text and the changes introduced by ISO 21920-2. Laboratories still cite PN-EN ISO 4287 in their scopes of accreditation — citing a withdrawn standard requires a deliberate decision agreed with the customer.

WHAT THIS STANDARD IS (ISO 4287:1997, clauses 1–2). The standard specifies terms, definitions and parameters for the determination of surface texture — roughness, waviness and primary profile — by profiling methods. It does not describe an instrument or a measurement procedure: the nominal characteristics of contact (stylus) instruments were given in ISO 3274:1996, the rules and procedures for the assessment of surface texture in ISO 4288:1996, and phase-correct filters in ISO 11562:1996 (normative references).

PROFILES AND FILTERS (clause 3). The surface profile is the intersection of the real surface with a specified plane. The primary profile (according to ISO 3274) is the basis for the primary profile parameters. The roughness profile is derived from the primary profile by suppressing the long-wave components with the λc filter; the λs filter separates roughness from even shorter components, and the λf filter defines the boundary between waviness and longer waves. The waviness profile is obtained by applying the λf and λc filters in turn. All three filters have the same transmission characteristic according to ISO 11562 but different cut-off wavelengths; the default relationship between λc and λs is given in ISO 3274.

PARAMETERS (second source — measuring instrument manufacturer guide, Mitutoyo 2021, according to ISO 4287:1997 with Amd 1:2009). Ra — arithmetic mean of the absolute ordinate values of the roughness profile within a sampling length; Rq — root mean square of the ordinates; Rp — largest profile peak height, Rv — largest profile valley depth, and Rz — the sum of these two, all within a sampling length; Rt — the same sum within the evaluation length; RSm — mean width of the profile elements within a sampling length. The same guide gives, after the instrument standards, stylus tip radii of 2 µm, 5 µm or 10 µm and a table of cut-off wavelengths λc (0.08; 0.25; 0.8; 2.5; 8 mm) with the corresponding λs (2.5; 2.5; 2.5; 8; 25 µm) and maximum tip radius (2; 2; 2; 5; 10 µm).

WHAT ISO 21920-2:2021 CHANGED. The first edition of ISO 21920-2 cancelled and replaced ISO 4287:1997 (with Amd 1:2009 and corrigenda) and ISO 13565-2 and 13565-3. The main changes compared with ISO 4287: all field parameters now relate to the evaluation length, profile elements are evaluated unambiguously, and new parameters were defined, in particular those based on the watershed transformation (details — Annex I of the standard, outside the available text). In text, parameters are written as abbreviated terms with lower-case suffixes, e.g. Rq.

WHAT WE DO NOT GIVE HERE. The parameter definitions of clause 4 of ISO 4287 and the new definitions of ISO 21920-2 — the available parts of both standards end with the general terms, and we give the definitions of Ra and Rz after the manufacturer guide. Rules for choosing the lengths, the number of sampling lengths and the rules for comparison with a tolerance (ISO 4288, now ISO 21920-3) — we did not have these texts. Typical Ra values for machining methods and conversions between Ra and Rz — the standard does not give them.

Method principle

The stylus of a contact instrument traverses the surface along a specified line, and the recorded primary profile is filtered: the λs filter removes the shortest waves and the λc filter separates roughness from waviness. Parameters are determined from the roughness profile, for example Ra (arithmetic mean of the absolute ordinates) and Rz (sum of the highest peak and the deepest valley within a sampling length according to ISO 4287). According to ISO 21920-2:2021, which replaced ISO 4287, field parameters relate to the evaluation length.

Applications

• Specifying and reading requirements for roughness, waviness and primary profile on drawings and in product specifications — terms and parameters of the profile method (ISO 4287, clause 1)
• Assessment of roughness after machining and comparison with the drawing tolerance — according to the rules of ISO 4288, now ISO 21920-3
• Transition of documentation and instrument software from ISO 4287 to ISO 21920-2 (change in the definition of field parameters)

Key parameters

Standard

Standard number

PN-EN ISO 4287:1999

Title (PL)

Specyfikacje geometrii wyrobów — Struktura geometryczna powierzchni: metoda profilowa — Terminy, definicje i parametry struktury geometrycznej powierzchni

Title (EN)

Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions and surface texture parameters

Step-by-step procedure

1. Establishing requirements

   Read from the drawing or specification which parameters (e.g. Ra, Rz) and limits are to be checked and according to which standard they are defined (ISO 4287 or ISO 21920-2).

2. Instrument set-up

   Choose the stylus and the λs and λc filters for the required parameter — the relationships are given in ISO 3274 and ISO 4288 (now ISO 21920-3); an example table: Mitutoyo guide.

3. Profile recording

   Traverse the stylus over the surface along a specified line and record the primary profile (ISO 4287, 3.1.4–3.1.5).

4. Filtering

   Obtain the roughness profile (λs and λc filters) or the waviness profile (λf and λc) according to ISO 11562 (3.1.6–3.1.7).

5. Calculating parameters

   Calculate the parameters over sampling lengths or the evaluation length according to the definitions of the standard in which the requirement is given.

6. Assessment and report

   Compare the results with the requirement according to the rules of ISO 4288 (now ISO 21920-3) and report the parameters, filters and the defining standard.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard contains no safety requirements; the rules for working with the instrument and with heavy workpieces are set by the laboratory on the basis of a risk assessment

Frequently asked questions