ISO/TR 27609:2007

TECHNICAL ISO/TR
REPORT 27609
First edition
2007-06-15

Vibration in hand-held tools — Vibration
measurement methods for grinders —
Evaluation of round-robin test
Vibration des machines à moteur portatives — Méthodes de mesure
des vibrations des meuleuses — Évaluation d'essais Round Robin




Reference number
ISO/TR 27609:2007(E)
©
ISO 2007

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ISO/TR 27609:2007(E)
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ISO/TR 27609:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Symbols and abbreviated terms .1
3 Method .3
4 Description of two test methods evaluated .3
4.1 Unbalance disc test method.3
4.2 Grinding test method .4
5 Results .4
5.1 General.4
5.2 Spread of methods .5
5.2.1 Unbalance disc test .5
5.2.2 Grinding test.8
5.2.3 Correlation between no-load and grinding vibration.10
5.3 Unbalance disc test for simulating real grinding .12
5.4 Measurements repeated over time.13
6 Conclusion .14
6.1 Unbalance disc test .14
6.2 Grinding test.14
6.3 Repeatability.14
Annex A (informative) Test instructions — “Instruction for participants in the 2003 round-robin
test on grinders. The aim is to evaluate the proposed changes to ISO 8662-4:1994 in
document ISO/TC 118/SC 3/WG 3 N211”.15
Annex B (informative) Diagrams.21
Annex C (informative) List of grinders and laboratories.28
Bibliography .29

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ISO/TR 27609:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 27609 was prepared by Technical Committee ISO/TC 118, Compressors and pneumatic tools,
machines and equipment, Subcommittee SC 3, Pneumatic tools and machines.
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ISO/TR 27609:2007(E)
Introduction
At the time of publication of this Technical Report, it was intended that ISO 8662-4, which deals with hand-
held grinders, be revised and harmonized with ISO 20643. The latter International Standard requires, among
other provisions, that the vibration emission measurements be made in three directions, with the declared
values related to the upper quartile of real-use vibration.
A round-robin test was made to gain an idea of the upper limits of real-use vibration and to establish a test
method fulfilling the three-direction requirement. Four grinders of different sizes — both with, and without,
auto-balancing units — were measured by seven laboratories. Measurements were made according to
detailed test instructions. The laboratories were manufacturers and health and safety authorities in Europe.
Two methods were evaluated by the round-robin test: one using a redesigned unbalance disc and the other by
grinding on mild steel using standard type 27 grinding wheels.
The result shows that the unbalance disc test method can be used for estimating the real-use vibration as long
as the grinder is not fitted with an auto-balancing unit. If such a unit is fitted, the real-use vibration is
underestimated by that method. Methods for estimating the real-use vibration level for grinders fitted with
auto-balancing units are not discussed in this Technical Report.
A real grinding test is not suitable for obtaining a declared value, as the spread for this method is large.
Furthermore, in order to obtain enough data to handle the large spread, the time consumption is unreasonably
high.

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TECHNICAL REPORT ISO/TR 27609:2007(E)

Vibration in hand-held tools — Vibration measurement methods
for grinders — Evaluation of round-robin test
1 Scope
This Technical Report presents an evaluation of a round-robin test of vibration measurement methods for
determining vibration in hand-held grinders. The aim of the round-robin test was to establish a test method
that could meet the requirement of ISO 20643 for measurement of vibration emissions in three directions, for
accordance with the planned-to-be-revised ISO 8662-4.
The value obtained by such a test method must correspond to the highest vibration values likely to occur
under typical and normal working conditions of the machine, i.e. the upper quartile of the vibration in real use.
This acknowledges that the upper boundary of “typical and normal” conditions can be exceeded by some
conditions of “real use”.
Vibration at grinding can mainly be divided into vibration caused by unbalance of the grinding wheel and
process vibration generated by the contact between the grinding wheel and the work piece. The unbalance
part has been shown to be the greater of the two and ISO 8662-4 is based on this. In this Technical Report,
the test method consists of a number of averaged measurements using an unbalance disc, with an unbalance
corresponding to the upper limit of the unbalances found among real grinding wheels.
Whereas ISO 8662-4 covers all types of hand-held grinders, the round-robin test presented in this Technical
Report was based on grinding with depressed centre-wheels, one of the most common grinding applications.
The types of grinder used in the round-robin test are given in Table 1.
Table 1 — Grinder types and sizes used in test
Wheel size
Type of grinder
125 mm 230 mm
(5'') (9'')
Pneumatic Without auto-balancing unit With auto-balancing unit
Electric With auto-balancing unit Without auto-balancing unit

Two tests of the grinders were made: one using an unbalance disc and the other by real grinding.
The unbalance disc test was made with a disc of new design, with the shape of a depressed centre wheel.
One reference disc was sent together with the grinding machines, while the other was locally manufactured by
the measuring lab. Grinding was made on mild steel with locally purchased grinding wheels. Detailed test
instructions were distributed to the participants before the start of the round-robin test.
2 Symbols and abbreviated terms
See Table 2.
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ISO/TR 27609:2007(E)
Table 2 — Symbols, abbreviated terms and their units
Symbols and
Description Unit
a
abbreviations
Vibration total value of frequency-massed r.m.s acceleration: root
2
a

m/s
hv
sum of squares of the a values for the three axes of vibration
hw
Arithmetic mean value of measurement results of runs and
2
a

m/s
h
operators: result of test
Coefficient of variation for test based on ratio of standard deviation
C
—
V,op
for operators(s ) and total mean value for all laboratories
op
Coefficient of variation of reproducibility for test based on ratio of
C standard deviation for laboratories(s ) and total mean value for all

—
V,R R
laboratories
G Grinding —
L 1…7 Laboratory making the measurement —
LD Locally made unbalance disc —
M1 125 mm grinder without auto-balancing unit, pneumatically powered —
M2 125 mm grinder with auto-balancing unit, electrically powered —
M3 230 mm grinder without auto-balancing unit, electrically powered —
M4 230 mm grinder with auto-balancing unit, pneumatically powered —
NL No-load —
RD Reference unbalance disc —
Standard deviation for operator, adjusted for the mean value of each
laboratory:
1
s=−aa
()
op ∑∑ ij, i

n− 1
2
s
ij
m/s
op
a value for operator j at laboratory i
ij,
a mean value for laboratory i
i
Standard deviation of reproducibility for laboratories according to
EN 12096:1997, A.10:
n
1 2
s=−aa
()

R ∑ i
2
s

n− 1 m/s
R
i=1
a results achieved at n different laboratories
i
a mean value for all laboratories
a
Other symbols and abbreviated terms are according to ISO 20643:2005.
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ISO/TR 27609:2007(E)
3 Method
The round-robin test was evaluated by studying the statistics of the data collected from the different tests and
labs using the following parameters.
⎯ Spread between operators
This parameter gives a measure of the expected spread on laboratory level for the methods.
⎯ Spread between laboratories
This parameter gives the total spread of the method. It includes the spread from operators, machines and
measuring equipment.
⎯ Repeatability
This parameter gives the stability of the method.
⎯ Correlation between grinding and no-load vibration
This parameter indicates in what extent grinding vibrations is dominated by unbalance or not.
In order to be able to compare values from the different sizes and types of grinder, the coefficient of variation
— the mean value divided by standard deviation — was used.
Significance tests were made using a double sided t-test with 95 % significance.
4 Description of two test methods evaluated
4.1 Unbalance disc test method
The new test wheel had tighter tolerances, thereby reducing the spread in unbalance from 2 % to 0,5 %. It had
a movable unbalance screw instead of a drilled hole, making it possible to vary the unbalance without
remounting the disc, and consequently simplifying the measurements and eliminating the uncertainty
introduced by loosening of the disc. The disc was shaped as a depressed centre wheel, see Figure 1.
Each lab measured the vibrations using two test wheels: one reference test wheel circulated through all test
labs (RD) and one manufactured by the measuring lab (LD).
A feed force equal to that recommended by ISO 8662-4:1994 was applied to the grinder during the test.

Figure 1 — Sketch of unbalance test disc (unbalance screw enlarged)
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ISO/TR 27609:2007(E)
4.2 Grinding test method
The grinding test was made on mild steel using depressed centre wheels (type 27). Each test session started
with a 10 s no-load measurement followed by 1 min of grinding and ending with a 10 s no-load measurement.
The mean value of the no-load measurements was taken as the estimated unbalance contribution to the
vibration during grinding. An example test measurement set-up is shown in Figure 2.
For each grinder, five grinding wheels were used, each operator grinding once with each wheel. According to
the test instructions (see Annex A), the grinding was made at the grinder’s maximum power by maximizing the
amount of sparks from the grinding process. The manner in which this was done differed from lab to lab.

Photo: Health and Safety Laboratory, UK
Figure 2 — Example of test set-up for grinding test
5 Results
5.1 General
During the round-robin test, the reference unbalance disc and screws were damaged, and thus could not
actually be used as the reference. However, in some cases they are reported separately.
On the M1 grinder, the hose was replaced by a quick coupling during the round-robin test. As a consequence,
the inertia and mass of the machine were changed, possibly affecting the vibration level. However, no
difference was detected that can be related to this change.
In some cases, large brackets were mounted at the support handle for attaching the feed force wire, thereby
also changing the inertia and mass of the machine. As with the case of quick coupling, no signs of differences
have been found that can be attributed to this change.
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ISO/TR 27609:2007(E)
Grinder M1 has a resonant support handle, making the grinder very sensitive to unbalance forces and
damping from the operator’s hand. Grip forces were therefore an important, but not recorded, parameter for
the vibration value from this grinder.
5.2 Spread of methods
The spread gives an indication of the repeatability and reproducibility of the test methods. The results are
presented in the following tables.
5.2.1 Unbalance disc test
The results from the unbalance disc test are separately presented for LD and RD, even though RD was
changed during the test round and cannot be used as reference disc. The result for both discs is presented in
the “Total” row. See Tables 3 and 4.
Table 3 — Emission values and standard deviations — Unbalance disc test
Max. handle Support handle Throttle handle

a s s a s s a s s

h op R h op R h op R
2 2 2 2 2 2 2 2 2

m/s m/s m/s m/s m/s m/s m/s m/s m/s
LD 14,33 2,65 3,75 14,33 2,65 3,75 7,34 0,33 1,05
M1
RD 14,68 2,88 4,59 14,68 2,88 4,59 7,16 0,37 0,81
Total 14,40 2,58 3,98 14,40 2,59 3,98 7,29 0,30 1,06
LD 7,58 0,47 1,84 5,10 0,58 0,64 7,58 0,47 1,84
M2
RD 6,99 0,59 1,44 4,78 0,62 0,97 6,99 0,59 1,44
Total 7,08 0,50 1,51 4,84 0,57 0,95 7,08 0,50 1,51
LD 10,60 0,88 0,91 6,74 0,37 0,62 10,60 0,88 0,91
M3
RD 9,82 0,54 1,49 6,50 0,30 0,18 9,82 0,54 1,49
Total 10,23 0,76 0,98 6,63 0,33 0,61 10,23 0,76 0,98
LD 2,25 0,08 0,30 2,06 0,08 0,25 2,23 0,08 0,40
M4 RD 2,18 0,12 0,26 2,10 0,11 0,25 2,15 0,13 0,29
Total 2,19 0,11 0,28 2,09 0,07 0,26 2,18 0,11 0,32

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ISO/TR 27609:2007(E)
A good measure of repeatability and reproducibility are, respectively, the coefficient of variation for operators
and the coefficient of variation for the laboratory, presented in Table 4.
Table 4 — Coefficient of variation — Unbalance disc test
Max. handle Support handle Throttle handle

C C C C C C

Ratio Ratio Ratio
V,op V,R V,op V,R V,op V,R
LD 0,18 0,26 0,70 0,18 0,26 0,70 0,04 0,14 0,31
M1
RD 0,20 0,31 0,63 0,20 0,31 0,63 0,05 0,11 0,46
Total 0,18 0,28 0,65 0,18 0,28 0,65 0,04 0,15 0,28
LD 0,06 0,24 0,26 0,11 0,13 0,91 0,06 0,24 0,26
M2 RD 0,08 0,21 0,41 0,13 0,20 0,64 0,08 0,21 0,41
Total 0,07 0,21 0,33 0,12 0,20 0,60 0,07 0,21 0,33
LD 0,08 0,09 0,97 0,05 0,09 0,60 0,08 0,09 0,97
M3
RD 0,05 0,15 0,36 0,05 0,03 1,67 0,05 0,15 0,36
Total 0,07 0,10 0,78 0,05 0,09 0,54 0,07 0,10 0,78
LD 0,04 0,13 0,27 0,04 0,12 0,32 0,04 0,18 0,20
M4
RD 0,06 0,12 0,46 0,05 0,12 0,44 0,06 0,13 0,45
Total 0,05 0,13 0,39 0,03 0,12 0,27 0,05 0,15 0,34
Average 0,09 0,19 0,44 0,10 0,16 0,54 0,06 0,15 0,36

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ISO/TR 27609:2007(E)
The coefficient of variation of reproducibility is about 25 % to 30 % for the 125 mm grinders and 10 % to 15 %
for the 230 mm grinders. A small value indicates a good reproducibility. The unbalance disc method has,
based on all unbalance disc measurements in this round-robin test, a C value of 0,2. The result for each
V,R
grinder is shown in Figure 3.

Key
X grinder
2
Y a , m/s
h
1 spread, lab
2 spread, operator
NOTE Two spread measures are presented: that between the operators and that between the different laboratories.
Figure 3 — All unbalance disc test method measurement results —
Average value and spread for all grinders
By taking the ratio between the total spread and operator spread, an estimate of the operators’ contribution to
the total spread can be obtained. For this method, the operator contributes 50 % to the total spread, which is
why the spread in unbalance of the unbalance disc is negligible. The spread of unbalance calculated
theoretically, with the tolerances given for the test tool, is less than 2 % compared to the operator spread.
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ISO/TR 27609:2007(E)
5.2.2 Grinding test
The results from the grinding test are presented in Tables 5 and 6 as the total average for all measurements
on each grinder.
Table 5 — Emission values and standard deviations — Grinding test
 Max. handle Support handle Throttle handle
a s s a s s a s s

h op R h op R h op R
2 2 2 2 2 2 2 2 2

m/s m/s m/s m/s m/s m/s m/s m/s m/s
G 7,28 1,02 2,46 7,28 1,02 2,46 4,61 0,73 2,26
M1
NL 8,97 1,40 2,91 8,97 1,40 2,91 4,82 0,41 1,96
G 5,43 0,89 2,43 4,66 0,89 2,34 4,99 0,58 1,72
M2
NL 4,84 0,34 1,19 3,99 0,35 0,76 4,84 0,35 1,39
G 9,42 1,05 1,59 7,75 0,96 1,84 9,31 0,88 1,21
M3
NL 5,95 0,59 1,44 5,49 0,51 1,57 5,86 0,50 1,23
G 3,48 0,43 1,00 3,48 0,43 1,00 2,83 0,28 0,95
M4
NL 1,75 0,20 0,26 1,68 0,17 0,29 1,65 0,19 0,25

Table 6 — Coefficient of variation — Grinding test
Max. handle Support handle Throttle handle

C C C C C C

Ratio Ratio Ratio
V,op V,R V,op V,R V,op V,R
G 0,14 0,34 0,41 0,14 0,34 0,41 0,16 0,49 0,41
M1
NL 0,16 0,32 0,48 0,16 0,32 0,48 0,09 0,41 0,48
G 0,16 0,45 0,37 0,19 0,50 0,38 0,12 0,34 0,38
M2
NL 0,07 0,25 0,29 0,09 0,19 0,46 0,07 0,29 0,46
G 0,11 0,17 0,66 0,12 0,24 0,52 0,09 0,13 0,52
M3
NL 0,10 0,24 0,41 0,09 0,29 0,32 0,09 0,21 0,32
G 0,12 0,29 0,43 0,12 0,29 0,43 0,10 0,34 0,43
M4
NL 0,11 0,15 0,77 0,10 0,17 0,58 0,12 0,15 0,58
Average 0,12 0,28 0,44 0,13 0,29 0,44 0,10 0,29 0,34

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ISO/TR 27609:2007(E)
The coefficient of variation of reproducibility was about 35 % for the 125 mm grinders and 20 % to 25 % for
the 230 mm grinders.
Based on all grinding measurements in the round-robin, the grinding test had a C value of 0,3. The result
V,op
for each grinder is shown in Figure 4.
The ratio between the total and the operator spread is in the same range as for the unbalance disc test, i.e. 2.

Key
X grinder
2
Y a , m/s
h
1 spread, lab
2 spread, operator
NOTE Two spread measures are presented: that between the operators and that between the different laboratories.
Figure 4 — All grinding test method measurement results —
Average value and spread for all grinders — Maximum handle
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ISO/TR 27609:2007(E)
5.2.3 Correlation between no-load and grinding vibration
One prerequisite for using the unbalance disc test method to estimate vibration at grinding is that the grinding
vibration is dominated by the grinding wheel’s unbalance. This can be verified by looking at the correlation
between no-load and grinding vibration.
As shown in Figure 5, there is a correlation between no-load and grinding vibration for the M3 grinder without
an auto-balancing unit.

Key
2
X no-load vibration, a , m/s
hv
2
Y grinding vibration, a , m/s
hv
NOTE Even though the spread is large, a correlation can be seen between no-load and grinding.
Figure 5 — All no-load values vs. grinding vibration for M3 — Support handle
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ISO/TR 27609:2007(E)
M4 does not show any signs of correlation between no-load and grinding, see Figure 6.
If the auto-balancing unit is badly designed, there can also be a correlation between no-load and grinding
vibration.

Key
2
X no-load vibration, a , m/s
hv
2
Y grinding vibration, a , m/s
hv
NOTE In this case there is no correlation between no-load and grinding.
Figure 6 — All no-load values vs. grinding vibration for M4 — Support handle
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ISO/TR 27609:2007(E)
5.3 Unbalance disc test for simulating real grinding
According to ISO 20643, a test method should result in a vibration value comparable to the upper quartile of
real use vibration. To test if that requirement can be fulfilled using the unbalance disc test method, the result
from the unbalance disc test was compared to the upper quartile vibration level from the grinding test.
As can be seen from Figure 7, the unbalance disc test values lie over the upper quartile vibration for grinding
with grinders without auto-balancing units, with a few exceptions. Thus, the unbalance disc test method can
be used for estimating the vibration at real grinding.
Grinders with auto-balancing units tested with unbalance disc tend to underestimate the vibration in real use;
therefore, an alternative method should be derived for them.

Key
X grinder
2
Y a , m/s
h
1 Al-disc
2 3rd quartile grinding
NOTE The only grinder that clearly lies under the upper quartile limit is M4, fitted with an auto-balancing unit.
Figure 7 — Emission value related to upper quartile for grinding — Maximum handle
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ISO/TR 27609:2007(E)
5.4 Measurements repeated over time
The repeatability over time is presented in Tables 7 to 10. It can also be used as a measure of repeatability of
the methods, in addition to the spread between operators. Four laboratories repeated the test on grinder M3.
The time between the first and second measurements was about a week.
Table 7 — Repeat of unbalance disc method for grinder M3 by four laboratories
Significant difference between measurements 1 and 2 — One to two weeks between tests
Support handle Throttle handle
L1 No No
L3 No No
L5 No No
L6
No No

Table 8 — Repeat of grinding test for grinder M3 made by four laboratories

Significant difference between measurements 1 and 2 — One to two weeks between tests
No-load Grinding
Support handle Throttle handle Support handle Throttle handle
L1
No No No No
L3
No No No No
L5 No No No No
L6 No No No No

Laboratory L5 repeated the entire round-robin test about a year after the first test. There was no significant
difference, at a 95 % significance level, between the results of the two unbalance disc tests. However, there
were significant differences between the first and second grinding tests, in all cases except for those of the M4
grinder (see Table 10).
Table 9 — Repeat of entire round-robin test by Laboratory 5 — Unbalance disc test
Significant difference between measurements 1 and 2 —

Approx. one year between tests
Support handle Throttle handle
M1
No No
M2
No No
M3 No No
M4 No Yes

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ISO/TR 27609:2007(E)
Table 10 — Repeat of entire round-robin test by Laboratory 5 — Grinding test


Significant difference between measurements 1 and 2 — Approx. one year between tests
No-load Grinding
Support handle Throttle handle Support handle Throttle handle
M1
Yes Yes Yes Yes
M2 Yes Yes Yes Yes
M3 Yes Yes Yes Yes
M4 Yes Yes No No

6 Conclusion
6.1 Unbalance disc test
The spread between operators, the smallest detectable spread in this test, is much higher than the theoretical
spread from the unbalance wheel itself. Thus, it would be possible to loosen the tolerances of, for example,
the mass of the unbalance screws or continue to use the current type of unbalance disc where the unbalance
is made by a hole in the disc.
The result of this method corresponds to the upper quartile of the vibration under the grinding test for grinders
without auto-balancing units. It does not apply to grinders fitted with auto-balancing units; therefore, it is
recommended that additional information be obtained from real grinding or other suitable methods.
6.2 Grinding test
The spread at grinding is 50 % to 100 % higher than the spread with test using the unbalance disc. The
difficulties using the same grinding techniques are probably contributing to this large spread. Thus real
grinding is not suitable as a test method for estimating the vibration in real-use.
6.3 Repeatability
Test with unbalance disc gives good repeatability in all repeatability tests here except for the 230 mm grinder
with auto-balancing unit. Though, it is already noticed that unbalance disc test is not the best method for
vibration testing of grinders with auto-balancing units. Grinding/no-load test can be repeated at the same
measurement occasion but gives poor repeatability when repeated with longer time between the tests.
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