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Evaluation of Roughness Measurements(DIN EN ISO 4288:1998)

Roughness measuring values - especially the vertical parameters (amplitude parameters) Rt,Rz, Rz1max and Ra- have a spread between -20 % and +30 %. A single measuring valuecan therefore not provide a complete statement concerning the observance of the permissibleparameter tolerances. DIN EN ISO 4288 Appendix A specifies the following procedure:

Max-rule:All roughness parameters with the addition maxas maximum value of the average value fromthe five single measured lengths: Measurement at at least three points on the surface where thehighest values are to be expected; the limit value must not be exceeded at any point.

16 %-ruleAll roughness parameters without the addition max as mean value from the five singlemeasured lengths:

16 % of the measuring values may exceed the limit value; step-by-step procedure:1. If the first measuring value is smaller than 70% of the limit value the latter is considered to beobserved.

2. Otherwise two further measurements at other points on the surface; if all three measuringvalues are smaller than the limit value, the latter is considered to be observed.

3. Otherwise nine further measurements at other points on the surface; if no more than twomeasuring values exceed the limit value, the latter is considered to be observed.

Drawing symbols (DIN EN ISO 1302:2002)

Basic symbola Single surface finish requirementb Further surface requirement

Materialremoval throughmechanicalmachining required

c Machining process (e.g. turned, ground, chrome-plated)

Material removalnot permissible

d Symbol for the directon of the surface groovese Machining allowance (in mm)

Identical texture for

all surfaces

x Letter for ease of benchmarking if space is limited

Entry at symbol (top)

Symbol for the direction of the surfacegroove (position d, bottom)

=

Parallel*

Vertical*)

X

Cross

*)... to the projection plane of the view in

Examples

No chip re

R-profile,

Chip remorule, maxiallowance

Chip remomeasuringroughness

Chip remorule, surfa}m (upper

Chip remorule, surfam (upper

Chip remo

P-profile, primary pr

Chip remo(=f=lw)

lengths (ln(upper lim

Chip remorule, total portion ofvalue)

Chip remogroove wilimit value

Explanatiospace is lim

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

The actual surface profile results from the intersection of the actual part surface with a planeperpendicular 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 aprobe. In doing so, the measured values are filtered thrugh the effect of the stylus tip radiusr

tipand - 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 bemeasured. If necessary, tolerances must be determined for this according to DIN EN I SO 8785.The primary profile is the profile after low-pass filtering the me asuring values using thecutoff wavelength

s. In doing so, the short-wave profile parts are cutoff. The parameters are

identified by P and evaluated wi thin the sampling length (cut-off). This equals the measuredlength or the length of the measured surface profile.

Fig. 1:Primary profile after Slow-pass filtering

The roughness profile results from high-pass filtering the primary profile with the cutoffwavelength

c. In doing so, the long-wave profile parts are cut-off. The parameters are

identified by R and evaluated over the measured l ength lnwhich is usually composed of fivesingle measured lengths lr.The single measured length corresponds to the cutoff wavelength

cof the profile filter.

Fig. 2:Roughness profile after Chigh-pass filtering with center line representation according to

EN ISO 4287

The waviness profileresults from low-pass filtering the primary profile with the cutoffwavelength

cand high-pass filtering with the cutoff wavelength

f. The parameters are

identified by Wand evaluated over the measured length Inwhich is composed of severalsampling lengths lw.The single measured length Iwcorresponds to the cutoff wavelength

f

of the high-pass filter. However, their number is not standardized and must therefore alwaysbe indicated on the drawing. It should range between five and ten. Profile filters

c(Fig. 3)

and fare applied successively. The waviness profile always results from application of both

filters (Fig. 4).

Fig. 3:Representation after clow-pass filtering

Fig. 4:Waviness profile after clow-pass filtering and

fhigh-pass filtering with center line representation

according to EN ISO 4287

Fig. 5:Transmissioncharacteristics of the filtersfor the different profiles,Gaussian filter according to

DIN EN ISO 11562:1998

Roughness parameters (DI

Ra Arithmetic mean surface rou

Rmr(c) Material proportion of lengths of the profile elements at thlength ln(specified in per cent)

RSm Average groove width: M(formerly S

m); for the evaluaton, horiz

Rt Total height of the roughneprofile peak and the depth Zvof the

Rzi Maximum height of the ro

profile peak and the depth of the low

Rz1max Maximum surface rosampling lenghts lr

iover the total me

Rz Surface roughness depth:Mlengths lr

iover the total measured le

Fig. 8:The average groovewidth RSmis the meanvalue of the width Xs

iof

the profile elements

Fig. 9:The material ratiocurve of the profile plotsthe material portion Rmr(c)of the profile as a functionof the section height c(Abbott-Firestone curve)

Profiles and filters

Roughness parameters

Preferred parameters

Measuring conditions

Evaluation

Drawing symbols

Fig. 6:Arithmetic averageroughness value Ra

Fig. 7:Total height ofthe roughness profile Rt,surface roughness depth

Rzand maximum surfaceroughness Rz1max