Surface Roughness – Practical tips for laboratory and workshop

Profiles and filters (DIN EN ISO 4287:1998 and DIN EN ISO 11562:1998)

The actual surface roughness profile results from the intersection of the actual part surface with a plane perpendicular to this surface. The plane should roughly be vertical to the machining grooves. The measured surface profile is the profile after tracing the actual surface profile using a probe. In doing so, the measured values are filtered through the effect of the stylus tip radius rtip and – where applicable – through the sliding skid of the probe system. Imperfections of the surface, like cracks, scratches and dents do not count as roughness and should not be measured. If necessary, tolerances must be determined for this according to DIN EN ISO 8785. The primary profile is the profile after low-pass filtering the measuring values using the cutoff wavelength λs. In doing so, the short-wave profile parts are cutoff. The parameters are identified by P and evaluated within the sampling length (cut-off). This equals the measured length or the length of the measured surface roughness profile.

Surface Roughness Chart

Fig. 1: Primary profile after λs low-pass filtering

The roughness profile results from high-pass filtering the primary profile with the cutoff wavelength λc. In doing so, the long-wave profile parts are cut-off. The parameters are identified by R and evaluated over the measured length ln which is usually composed of five single measured lengths lr. The single measured length corresponds to the cutoff wavelength λc of the profile filter.

Surface Roughness Measurement

Fig. 2: Roughness profile after λc high-pass filtering with center line representation according to EN ISO 4287

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