Precise roughness measurement

Surface texture parameters

in practice
 Surface texture measurement

Surface texture measurement with Jenoptik

Surface texture is very important where it has a direct influ-

ence on the quality of the part. Therefore, it has to be defined
as precisely as possible with the help of standardized surface
texture parameters.

This leaflet gives you an overview of the most important

­definitions, standards, and parameters of surface texture
­measurement.

We manufacture a wide range of roughness measuring systems

providing you with a large variety of evaluation possibilities – in
the measuring lab as well as on the production line.

One particularly important aspect is the continuous monitoring

of the roughness measuring systems for optimum accuracy.
Our DAkkS-DKD calibration laboratory can calibrate your
standards based on different surface texture parameters. For
parameters not requiring accreditation, we offer an in-house
calibration certificate.

Division of a surface
Unfiltered P-profile

Filtered W-profile

Filtered R-profile

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 Surface texture measurement

Surface profiles – total height of the profile

Surface profile is measured two-dimensionally using the tracing

system.

The unfiltered primary profile (P-profile) is the actual measured

surface profile. Filtering it in accordance with ISO 11562/ISO
16610-21 produces the waviness profile (W-profile) and the
roughness profile (R-profile). The variable for determining the
limit between waviness and roughness is the cut-off λc.

Following ISO 4287, all parameter definitions are valid for both
the roughness profile as well as for the primary and waviness
profiles. The profile type is identified by the capital letters P, R
or W.

The total height Pt, Wt or Rt of the respective profile type is the

maximum height between the highest peak and the deepest
valley of the evaluation length profile.

Evaluation lengths – cut-off

Start-up length Roughness profile Run-off length

The traverse length (lt) is the total length of the probe move-
ment during the scanning process. It must be greater than the
evaluation length ln in order to be able to form the roughness
profile with the profile filter.

With the exception of Rt, Rmr(c) and RPc, the roughness

parameters are defined within an evaluation length ln, which is
determined using an average of five sampling lengths lr.

The sampling length lr corresponds to the cut-off λc.

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 Measurement conditions

Selection of the cut-off (profile filter) according to ISO

The cut-off is selected depending on the workpiece surface

either according to the valley spacing, or the expected rough-
ness values. At the same time the total evaluation length and

Periodic profiles Measurement conditions

e.g. turning, milling
lr sampling length
RSm
ln evaluation length
lt traverse length
λc cut-off
λs shortwave profile filter
rtip stylus tip radius
ΔX digitization distance 1)

RSm (mm) λc = lr (mm) ln (mm) lt (mm)

> 0.013 ...0.04 0.08 0.4 0.48
> 0.04 ...0.13 0.25 1.25 1.5
> 0.13 ...0.4 0.8 4 4.8
> 0.4 ...1,3 2.5 12.5 15
> 1.3 ...4 8 40 48

Application example
In a periodic profile the mean width of the profile elements RSm is used. With
an RSm between 0.4 and 1.3 mm the following measuring conditions result:
λc = 2.5 mm / ln = 12.5 mm / lt = 15 mm / rtip = 5 µm / λs = 8 µm.
* At Rz ≤ 2 μm the stylus tip radius is 2 μm, at Rz > 2 μm it is 5 μm.
The distance between two measuring points is ≤ 0.5 μm.

Measurement conditions for Motif parameters according

A* (mm) B* (mm) Traverse length (mm)

0.02 0.1 0.64
0.1 0.5 3.2
0.5 2.5 16
2.5 12.5 80

* If not otherwise specified, the default values are A = 0.5 mm and B = 2.5 mm, respectively. The defined limit A

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 Measurement conditions

4288:1998 and ISO 3274:1998

the corresponding traverse length are defined according to

standards. Deviations are necessary if the workpiece does not
allow the required traverse length. See drawing entries.

Aperiodic profiles
1)
The digitization e.g. grinding, eroding
distance is also stan­
dardized. This is set Rz
automatically by most
roughness measuring
instruments.

rtip (µm) λs (µm) Ra (µm) Rz (µm)

2 2.5 > (0.006) …0.02 > (0.025) …0.1
2 2.5 > 0.02 …0.1 > 0.1 …0.5
2 or 5 * 2.5 > 0.1 …2 > 0.5 …10
5 8 >2 …10 > 10 …50
10 25 > 10 …80 > 50 …200

Shortened standard evaluation length

If the actual possible traverse length on the workpiece surface is not enough for
lt, the number of sampling lengths is reduced accordingly and specified in the
drawing.

If the actually available traverse length is less than a sampling length, the total
height of profile Pt of the primary profile is evaluated instead of Rt or Rz.

to ISO 12085

Evaluation length (mm) λs (µm) Max. stylus tip radius (µm)

0.64 2.5 2 ± 0,5
3.2 2.5 2 ± 0,5
16 8 5±1
80 25 10 ± 2

determines in this case that the measured AR parameters are always smaller than 0.5 mm.

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 Surface texture parameters

Ra according to ISO 4287

Center line

Ra – arithmetical mean deviation

Ra is the arithmetic mean roughness value from the amounts
of all profile values. Ra does not differentiate between peaks
and valleys and has therefore a relatively weak information
character.

Rz, Rz1max, Rt according to ISO 428

Rz – maximum height of profile

Average value of the five Rz values.

Rz1max – maximum height of profile (ISO 4287:1997)

Greatest Rz value from the five sampling lengths lr.

Rt – total height of profile

Rt is the distance between the highest peak and the deepest
valley of the profile of the total evaluation length ln.

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 Surface texture parameters

RSm according to ISO 4287

Center line

RSm – mean width of the profile elements

RSm is the arithmetic mean value of the width of the roughness
profile elements within the sampling length and requires the
definition of height discriminations (c1, c2) matching the func-
tion of the surface. If not specified otherwise, the sum of the
height discriminations should add up to 10 % of Rz.

RPc according to EN 10049/ISO 4287

Center line

RPc – standardized number of peaks

RPc corresponds to the number of local peaks, which succes-
sively exceed an upper section line c1 and a lower section
line c2. The number of peaks is related to a length of 10 mm
irrespective of the evaluation length selected.

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you optimum support as a reliable partner.

Copyright © JENOPTIK Industrial Metrology Germany GmbH. All rights reserved. Subject to change without notice.

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 Surface texture parameters

Rmr(c) according to ISO 4287

Reference line
Reference section height c0

Section height c

Material
ratio curve

Evaluation length In
Material ratio Rmr (c)

Rmr(c) – material ratio of the profile

Rmr indicates what ratio the totaled length in the material has
assumed relative to the evaluation length (in %). The com-
parison is made in the specified section height c and the total
­evaluation length ln. The material ratio curve indicates the
material ratio as a function of the section height.

Rk, Rpk, Rvk, Mr1, Mr2

according to ISO 13565-2
„Peak surface“
Rpk*

Material ratio curve

Rpk

Profile peak section

Core
„Valley surface“
Rk
Rvk*

Material ratio
Rvk

Profile valley section

Rk – core roughness depth

Depth of the roughness core profile.
Rpk – reduced peak height
Mean height of the peaks protruding from the roughness profile.
Rpk* – highest profile peak height (not ISO 13565-2)
Rvk – reduced valley depth
Mean depth of the valleys reaching into the material from the core.
Rvk* – deepest profile valley depth (not ISO 13565-2)
Mr1, Mr2 – material ratio
Smallest (Mr1) and greatest (Mr2) material ratio (in %) at the
limits of the roughness core area.

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 Surface texture parameters

Motif standard according to ISO 12085

The principle of the Motif standard consists of looking for local
peaks and valleys in the primary profile, and associating one
valley with the closest preceding and following peaks in order
to create a Motif. Several iterative combinations of two Motifs
each assure that the most important Motifs, the width of which
fall below the limit A, are considered. If not otherwise specified,
the default value is A = 0.5 mm (see measurement conditions
page 4/5).
The limit A has a similar function as the cut-off in the Gaussian
filtering. The 16 % rule generally applies.
H j
H j+1

Hm-1
Hm
H 3
H 2
H 1

AR1 AR i AR n

The most important Motif parameters:

R – Mean depth of roughness Motifs
R is the arithmetic mean value of the depths Hj of the rough-
ness Motifs within the evaluation length.

AR – Mean spacing of roughness Motifs

AR is the arithmetic mean value of the lengths ARi of the
roughness Motifs within the evaluation length.

Rx – Maximum depth of profile irregularity

The deepest depth Hj within the evaluation length.

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 Surface texture parameters

WDSm, WDt, WDc –

Dominant waviness according to VDA 2007
The primary profile is checked for none, one or two dominant
wavinesses. Narrow band filtering of the primary profile with
the waviness creates the WD-profile that is used for calculat-
ing the parameters. The evaluation length ln is chosen either
according to ISO 4288 (as for surface roughness measurements)
or on the basis of the drawing entry.
Period lengths are checked for dominant wavinesses in
the range of 0.02 mm ≤ WDSm ≤ ln/5. To catch dominant
­wavinesses at WDSm > ln/5, it is n
­ ecessary to enlarge the
­evaluation length.
WDt WDSm

Evaluation length ln
P-profile WD-profile

WDSm
Mean horizontal value of the profile elements, calculated from
the amplitude spectrum (mean periodic length of the dominant
waviness).

WDt
Vertical difference between the highest and the deepest point
of the WD-profile within the evaluation length.

∆Z1 ∆Z2 ∆Z3 ∆ZN-1 ∆ZN

Evaluation length ln

P-profile WD-profile

WDc
Mean value of the peaks of the profile elements within the
evaluation length.

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 Evaluation

Evaluation of measurement results

According to ISO 4288 the surface measurement should

be made where the highest values are to be expected (visual
determination).

Maximum value rule

The surface is considered good when the measured values of a

parameter do not exceed the fixed maximum value. In this case,
the parameter is identified by the suffix „max“, e.g. Rz1max.

16 % rule

If the suffix „max“ is not specified, the 16 % rule applies,

which states that the surface is considered “good” if not more
than 16 % of the measured parameter values exceed the fixed
maximum value. You will find further information about this
rule in the standard ISO 4288:1997.

Special rule VDA

The 16 % rule is not used. VDA 2006 assumes that the disper-
sion of the parameters is taken into account in the definition of
the limit values. The maximum value rule applies generally even
without the „max“ index in the designation. The use of the λs
filter is prohibited.
At Rz ≤ 2 μm the stylus tip radius is 2 μm, at Rz > 2 μm it is
5 μm. The distance between two measuring points is ≤ 0.5 μm.
The cone angle is either 60° or 90°. If not otherwise specified,
it is 90°.

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 Drawing entries

Drawing entries according to ISO 1302:2002

Specifications for requirements

a surface parameter with numeric value in μm
c b second requirement (surface parameter in μm)
c production method
a d specification of valley direction
e d b e machining allowance in mm

Rz 4 L Rz 2.5

Material removing Material removing

machining; machining; lower limit
Rz = max. 4 μm value for Rz demanded;
Rz = min. 2.5 μm

U Ra 4
L Ra 1 Rzmax 4

Material removing Material removing

machining; upper and machining;
lower limit value for Ra Rz = max. 4 μm;
demanded; the maximum value rule
Ra = min. 1 μm and applies
max. 4 μm

2/Pt 4 0.008-2.5/Rz1

Material removing Material removing machining; transmission characte-

machining; P-profile, ristic does not comply with standard case (cf. table)
traverse length = 2 mm; Rz = max. 1 μm; filter selection λs = 0.008 mm and
Pt = max. 4 μm λc = 2.5 mm

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 Drawing entries

Drawing entries according to VDA 2007 –

dominant waviness

Case 1: No dominant waviness allowed

WDc 0

Material removing
machining; WDc 0 or
WDt 0: no dominant
waviness allowed

Case 2: Dominant wavinesses are allowed up to

an upper limit

2.5x5/WDt 2.5

Material removing machining; in

the period range up to 2.5 mm,
WDt = max. 2.5 μm applies

Case 3: Dominant wavinesses are allowed in a period length

with an upper or an upper and lower limit

0.8x16/Rz 3
0.2-2.5x5/WDc 1.5

Material removing machining;

Rz: the evaluation length is 12.5 mm
and λc = 0.8 mm, Rz = max. 3 μm;
WDc: in the period range of 0.2 to
2.5 mm, WDc = max. 1.5 μm applies

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