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 2007
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ii © ISO 2007 – All rights reserved

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

Foreword
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(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
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In exceptional circumstances, when a technical committee has collected data of a different kind from that
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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informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.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.
iv © ISO 2007 – All rights reserved

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.
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.
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
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
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:
s=−aa
()
op ∑∑ ij, i
n− 1
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
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.
2 © ISO 2007 – All rights reserved

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
Th
...