Edge Roughness Measurement: Rz5, Ra & Profile Methods for Laser Cutting

Q: What is Rz5 in laser cutting?

Rz5 is the mean peak-to-valley roughness averaged over 5 consecutive sampling lengths on a cut edge, as defined by ISO 9013. It is the primary metric for laser cut surface quality. For 6mm carbon steel on a fiber laser, typical Rz5 values are 15-30 μm (Range 1-2). Lower Rz5 means smoother cut surface with less visible drag lines.

Q: How do I measure cut edge roughness?

Three common methods: (1) Contact profilometer — most accurate, traces a stylus across the surface and records the profile. (2) Portable surface roughness tester — compact handheld devices (Mitutoyo SJ-210, Mahr MarSurf) suitable for production QC. (3) Visual comparison with ISO 9013 reference samples — fastest for go/no-go decisions in production.

Q: What is the difference between Ra and Rz5?

Ra is the arithmetic mean deviation — the average of all surface deviations from the mean line. Rz5 is the mean peak-to-valley height over 5 sampling lengths. Rz5 is more sensitive to isolated deep scratches or drag lines, making it the preferred metric for laser cut quality per ISO 9013. Roughly: Rz5 ≈ 4-6 × Ra for typical laser cut surfaces.

⚡ Key Takeaway

Rz5 is the standard metric for laser cut edge quality per ISO 9013. Measure it with a portable profilometer at mid-height on the cut edge. Target Rz5 < 30μm for precision work (ISO 9013 Range 1-2). Visual reference charts enable rapid production QC without instruments.

Edge roughness is the most visible indicator of cut quality. This guide covers the measurement methods, equipment, and interpretation techniques used in production facilities. For the full quality classification system, see our ISO 9013 Practical Guide.

Published: February 11, 2026

Last Updated: February 11, 2026

Skill Level: Advanced / Quality Inspector

1. Key Roughness Metrics

Metric	Definition	ISO Standard	Use Case
Rz5	Mean peak-to-valley height over 5 sampling lengths	ISO 9013	Primary laser cut metric
Ra	Arithmetic mean deviation from mean line	ISO 4287	General engineering drawings
Rz	Maximum peak-to-valley in single sampling length	ISO 4287	Identifying isolated defects
Rt	Total height of profile (max peak to max valley)	ISO 4287	Worst-case assessment

Conversion rule of thumb: For typical laser cut edges, Rz5 ≈ 4-6 × Ra. So Ra = 5μm corresponds to approximately Rz5 = 20-30μm. However, this ratio varies with surface profile — always measure the metric specified on the drawing.

2. Measurement Methods

Contact Profilometer

Most Accurate

A diamond stylus (2μm tip radius) traces across the surface. The vertical displacement is recorded as the surface profile.

Resolution: 0.01 μm vertical

Equipment: Mitutoyo SJ-210, Mahr MarSurf M300

Cost: $2,000-8,000

Time per measurement: 30-60 seconds

Optical / Non-Contact

Fastest, No Surface Contact

Laser confocal or white-light interferometry scans the surface without touching it. Captures full 3D surface map.

Resolution: 0.001-0.01 μm vertical

Equipment: Keyence VR-6000, Zygo NewView

Cost: $15,000-50,000

Time per measurement: 5-15 seconds

Visual Comparison

Production QC

Compare cut edge against reference samples with known Rz5 values. Fastest method for go/no-go decisions.

Resolution: ±20% of Rz5 range

Equipment: ISO 9013 reference set

Cost: $200-500

Time per measurement: 5-10 seconds

3. Step-by-Step Measurement Procedure

Select measurement zone: Measure at mid-height of the cut edge (50% of material thickness). Exclude top 10% (melt zone) and bottom 10% (re-solidification / burr zone).

Orient the probe: The stylus must travel perpendicular to the drag lines (i.e., horizontally across the cut face). Measuring parallel to drag lines produces artificially low readings.

Set sampling length: ISO 4287 defines the cutoff wavelength λc based on expected roughness. For laser cuts (Rz5 10-50μm), use λc = 0.8mm, evaluation length = 4mm (5 × λc).

Take 3+ measurements: Measure at different positions along the cut edge (start, middle, end). Report the average and maximum values. ISO 9013 compliance requires the maximum to be within the tolerance range.

Document results: Record Rz5 value, material, thickness, measurement position, equipment used, and date. For ISO 9013 reporting, state the quality range achieved.

4. How to Improve Edge Roughness

Parameter Adjustments

• Reduce cutting speed by 5-10% (allows cleaner melt ejection)

• Optimize focus position (most impactful single parameter)

• Increase assist gas pressure for better slag removal

• Use nitrogen assist for stainless steel (oxide-free edge)

• Fine-tune pulse frequency for pulsed cutting modes

Equipment Maintenance

• Replace nozzle when centering deviation > 0.03mm

• Clean protective lens — contamination causes beam scatter

• Check beam alignment / collimation monthly

• Verify gas purity (> 99.95% for N₂ on stainless)

• Inspect cutting head for internal contamination

Frequently Asked Questions

What is Rz5 in laser cutting?

Rz5 is the mean peak-to-valley roughness averaged over 5 sampling lengths on the cut edge, defined by ISO 9013. It is the standard metric for thermal cut quality classification. Typical fiber laser values: 15-30μm for thin sheet, 30-60μm for medium plate.

What is the difference between Ra and Rz5?

Ra averages all deviations. Rz5 measures peak-to-valley height. Rz5 catches deep scratches that Ra averages out. For laser cuts: Rz5 ≈ 4-6× Ra. ISO 9013 specifies Rz5; general engineering drawings often use Ra.

How do I measure cut edge roughness quickly?

For production QC, visual comparison against ISO 9013 reference samples (5-10 seconds). For documentation, use a portable contact profilometer (30-60 seconds per reading). Full profile analysis with optical systems is used for process development and troubleshooting, not routine QC.

Related Guides

Edge Quality Standards

Complete edge quality assessment

ISO 9013 Practical Guide

Full quality classification system

Focus Position Guide

#1 parameter for roughness control

Measurement procedures follow ISO 4287:1997 (surface roughness parameters) and ISO 9013:2017 (thermal cutting quality). Equipment recommendations are based on common metrology instruments available from major manufacturers. Always calibrate instruments per manufacturer specifications before measurement.