📏 Surface roughness measurement (Ra, Rz)
In short
Measurement of surface roughness parameters (Ra, Rz, Rq, Rp, Rv) by profile method using contact profilometer. The test is performed according to PN-EN ISO 4287:1999; Ra (arithmetic mean): 0.006–100 µm (typically 0.1–12.5 µm). The procedure comprises 10 steps (about 26–32 min in total); it is used for: Quality control of engine components (cylinders, shafts, pistons, valves), Quality acceptance after machining (turning, milling, grinding, honing), Roughness measurement of galvanic and paint coatings.
At a glance
- Standard: PN-EN ISO 4287:1999
- Category: Automotive
- Procedure steps: 10
- Total time of stages: 26 min–32 min
- Ra (arithmetic mean): 0.006–100 µm (typically 0.1–12.5 µm)
- Rz (max. profile height): 0.025–400 µm (Rz ≈ 4×Ra indicative)
- Stylus radius: 2 µm (standard) or 5 µm
Overview
Surface roughness is one of the most important quality parameters of industrial products, directly affecting friction, wear, tightness, fatigue strength, coating adhesion, aesthetics and functionality of components. Standard PN-EN ISO 4287 defines terminology and parameters of profile surface texture.
The most commonly used parameters are: Ra (arithmetic mean roughness — average absolute value of profile ordinates from mean line) and Rz (maximum profile height — sum of largest peak and deepest valley in elementary section, averaged from 5 sections). Other parameters are Rq (root mean square), Rp (max. peak), Rv (max. valley), RSm (mean width of profile element).
In automotive, roughness is critical: cylinder surfaces (honing with precise Ra required), crankshafts, bearing journals, gears, brake system components. In technical cleanliness (VDA 19 / ISO 16232) roughness affects particle contamination adhesion. In machining (turning, milling, grinding) roughness is acceptance parameter for each operation.
Measurement is performed with contact profilometer — diamond stylus (radius R = 2 or 5 µm) moves across surface at specified speed, and inductive transducer records vertical deviations. Modern profilometers provide digital profile processing with Gaussian filtration (separation of roughness from waviness).
Method principle
Contact profilometer records surface profile — diamond stylus with tip radius 2 µm (or 5 µm) moves across tested surface at constant speed (0.5–1 mm/s). Vertical stylus deviations are converted by inductive transducer into electrical signal, digitized and analyzed. Raw profile is filtered with Gaussian filter — profile filter λs cuts off noise, filter λc separates roughness from waviness (λc = 0.08–8 mm according to ISO 4288). Parameters Ra, Rz and others are calculated based on roughness profile within measurement length = 5 × elementary section (lr).
Applications
- Quality control of engine components (cylinders, shafts, pistons, valves)
- Quality acceptance after machining (turning, milling, grinding, honing)
- Roughness measurement of galvanic and paint coatings
- Technical cleanliness — correlation of roughness with particle adhesion (VDA 19)
- Quality control of cutting tools and injection molds
- Tribological measurements — assessment of bearing, guide, seal surfaces
- Certification of aerospace and medical components (FDA, EASA requirements)
- Comparative tests of machining and surface finishing processes
Key parameters
| Parameter | Value |
|---|---|
| Ra (arithmetic mean) | 0.006–100 µm (typically 0.1–12.5 µm) |
| Rz (max. profile height) | 0.025–400 µm (Rz ≈ 4×Ra indicative) |
| Stylus radius | 2 µm (standard) or 5 µm |
| Elementary section length (lr) | 0.08 / 0.25 / 0.8 / 2.5 / 8 mm (according to ISO 4288) |
| Traverse speed | 0.5–1 mm/s (measurement), up to 3 mm/s (fast scan) |
| Vertical resolution | 0.001–0.01 µm (workshop profilometers: 0.01–0.1 µm) |
Standard
- Standard number
- PN-EN ISO 4287:1999
- Title (PL)
- Specyfikacje geometrii wyrobów (GPS) — 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
-
Surface preparation
Clean tested surface from grease, dust and contamination (isopropanol, lint-free cloth). Dry.
-
Profilometer calibration
Measure roughness standard (etalon Ra e.g. 3.2 µm). Compare result with certified value. Deviation ≤5%.
-
Measurement parameter setting
Select parameters: standard (ISO 4287), filter (Gauss), cut-off λc (according to ISO 4288 — e.g. 0.8 mm for Ra 0.1–2 µm), number of sections (5).
-
Stylus positioning
Place profilometer on tested surface. Stylus perpendicular to machining marks. Lower head to contact with surface.
-
Measurement execution
Start stylus traverse. Profilometer records profile over measurement length (5 × lr + 2 × lr run-up). Time ~5–30 s.
-
Parameter reading
Profilometer displays: Ra, Rz, Rq, Rp, Rv, RSm and other selected parameters. Optionally profile graph.
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Measurements at multiple locations
Perform min. 3 measurements at different locations and directions on tested surface. Calculate mean and scatter.
-
Comparison with requirements
Compare results with technical drawing tolerances (e.g. Ra ≤ 1.6 µm). Assess compliance. Issue judgment.
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Documentation
Record: measurement parameters (λc, standard), measurement locations, Ra/Rz results, profile (optionally printout or PDF). Archive.
-
Profilometer maintenance
Clean stylus with compressed air. Check tip condition (microscopically every 500 measurements). Replace worn stylus.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Portable contact profilometer | Mitutoyo SJ-210, Mahr MarSurf PS 10, Taylor Hobson Surtronic S-128 | 8 000–25 000 PLN |
| Stationary contact profilometer | Mitutoyo SJ-412, Mahr MarSurf GD 26, Taylor Hobson Form Talysurf | 40 000–200 000 PLN |
| Roughness standard (etalon) | Halle Ra 0.4/3.2 µm, Mitutoyo 178-602, PTB/GUM certificate | 1 500–5 000 PLN |
| Granite measuring table | Mitutoyo, TESA, grade 0/1, with antivibration supports | 3 000–15 000 PLN |
| Measuring head / motorized arm | Mitutoyo 178-390, motor drive with speed adjustment | 5 000–20 000 PLN |
| Profile analysis software | Mitutoyo SJ-Tools, Mahr MarWin, Taylor Hobson Ultra | 3 000–15 000 PLN (license) |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Roughness standard Ra 0.4 µm | — | Metal etalon with certified Ra, for profilometer calibration, traceable to PTB/GUM |
| Roughness standard Ra 3.2 µm | — | Metal etalon, second calibration point, accredited certificate |
| Cleaning fluid / degreaser | 67-63-0 | Isopropanol (IPA), for cleaning measured surface from grease and contamination |
Health and safety (OHS)
- Diamond stylus — very sharp and brittle, risk of damage with careless handling
- Isopropanol — flammable, vapors irritate respiratory tract, workstation ventilation
- Heavy components for measurements (e.g. engine blocks) — ergonomics, hoists
- Stationary profilometer — protection against vibrations (granite table, pneumatic cushions)
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 4287:1999 — “Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions and surface texture parameters”.
How does this method work?
Contact profilometer records surface profile — diamond stylus with tip radius 2 µm (or 5 µm) moves across tested surface at constant speed (0.5–1 mm/s).
What is the measuring range and accuracy?
Ra (arithmetic mean): 0.006–100 µm (typically 0.1–12.5 µm); Rz (max. profile height): 0.025–400 µm (Rz ≈ 4×Ra indicative); Stylus radius: 2 µm (standard) or 5 µm; Elementary section length (lr): 0.08 / 0.25 / 0.8 / 2.5 / 8 mm (according to ISO 4288).
How long does the test take?
The times given for the individual stages add up to approximately 26 min–32 min. The procedure comprises 10 steps.
What equipment is required?
Portable contact profilometer, Stationary contact profilometer, Roughness standard (etalon), Granite measuring table, Measuring head / motorized arm, Profile analysis software. Indicative cost of the core instrument (Portable contact profilometer): 8 000–25 000 PLN.
Where is this test used?
Quality control of engine components (cylinders, shafts, pistons, valves); Quality acceptance after machining (turning, milling, grinding, honing); Roughness measurement of galvanic and paint coatings; Technical cleanliness — correlation of roughness with particle adhesion (VDA 19); Quality control of cutting tools and injection molds; Tribological measurements — assessment of bearing, guide, seal surfaces; Certification of aerospace and medical components (FDA, EASA requirements); Comparative tests of machining and surface finishing processes.
What safety precautions apply?
Diamond stylus — very sharp and brittle, risk of damage with careless handling; Isopropanol — flammable, vapors irritate respiratory tract, workstation ventilation; Heavy components for measurements (e.g. engine blocks) — ergonomics, hoists; Stationary profilometer — protection against vibrations (granite table, pneumatic cushions).
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 4287.