ISO/TR 10064-1:2017

Code of inspection practice - Part 1: Measurement of cylindrical gear tooth flanks

ISO/TR 10064-1:2017 supplements ISO 1328‑1:2013. It provides a code of practice dealing with measurements on flanks of individual cylindrical involute gears, i.e. with the measurement of pitch, profile, helix and tangential composite characteristics. It describes measuring equipment, provides advice for gear measuring methods and for the analysis of measurement results, and discusses the interpretation of results. Measurements using a double flank tester are not included (see ISO/TR 10064‑2). This document only applies to involute gears.

Code pratique de réception — Partie 1: Mesure des flancs dentaires cylindriques

General Information

• Status: Withdrawn
• Publication Date: 11-Jul-2017
• Withdrawal Date: 11-Jul-2017
• ICS: 21.200 - Gears
• Technical Committee: ISO/TC 60 - Gears
• Drafting Committee: ISO/TC 60/WG 2 - Accuracy of gears
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 11-Sep-2019
• Completion Date: 27-Dec-2025

Relations

• Consolidated By: ISO 10893-8:2011/Amd 1:2020 - Non-destructive testing of steel tubes - Part 8: Automated ultrasonic testing of seamless and welded steel tubes for the detection of laminar imperfections - Amendment 1: Change acceptance criteria
• Effective Date: 06-Jun-2022
• Revised: ISO/TR 10064-1:2019 - Code of inspection practice - Part 1: Measurement of cylindrical gear tooth flanks
• Effective Date: 23-Apr-2020
• Revises: ISO/TR 10064-1:1992/Cor 1:2006 - Code of inspection practice - Part 1: Inspection of corresponding flanks of gear teeth - Technical Corrigendum 1
• Effective Date: 05-Nov-2015
• Revises: ISO/TR 10064-1:1992 - Code of inspection practice - Part 1: Inspection of corresponding flanks of gear teeth
• Effective Date: 04-Nov-2015

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 10064-1
Second edition
2017-07
Code of inspection practice —
Part 1:
Measurement of cylindrical gear
tooth flanks
Code pratique de réception —
Partie 1: Mesure des flancs dentaires cylindriques
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
4 General considerations . 5
4.1 Background . 5
4.2 Required inspection information . 5
4.3 Measurement selection . 5
4.3.1 Substitution of measurement methods . 5
4.3.2 First piece inspection . 5
4.3.3 Sampling and statistical process control . 5
5 Conventions and measurement positions . 6
5.1 General . 6
5.2 Datum axis . 6
5.3 Left or right flank . 6
5.4 Left hand or right hand helical gears . 7
5.5 Numbering of teeth and flanks . 7
5.6 Numbering of pitches . 8
5.7 Number of pitches “k” in a deviation symbol subscript . 8
6 Types of measuring equipment and principle . 8
6.1 General . 8
6.2 Measurement methods .14
6.2.1 Generative measurement methods .14
6.2.2 Non-generative measurement methods .16
6.2.3 Pitch measurement methods .17
6.2.4 Hand-held pitch measuring devices .18
6.2.5 Radial runout measurement .20
6.2.6 Computer tomography methods for small gears .21
6.2.7 Optical devices for small spur gears .21
6.3 Calibration of equipment .22
6.4 Tooth thickness, differences between CNC/CMM and manual measurement .22
6.5 “In-process” gear measurement on manufacturing machines .23
6.6 Gear mounting .23
6.7 Example output format from a CNC GMM .24
6.7.1 General.24
6.7.2 Example evaluations of modified helices and profiles .27
7 Recommended measurement procedure and good measurement practice .28
7.1 Measurement procedure .28
7.2 Probe problems when measuring aluminium parts .30
7.3 Suitable artefacts for calibration of measuring machines .30
8 Inspection procedures for gears that are too large for gear inspection machines .31
8.1 General .31
8.2 Profile inspection using portable device .31
8.2.1 Disassembly of segments .31
8.2.2 Measurement by portable gear inspection device using coordinates .31
8.2.3 Profile inspection by gear tooth caliper .32
8.3 Inspection of helix form deviation .36
8.3.1 Inspection of helix form deviation on the gear cutting machine.36
8.3.2 Straightness inspection using a cylinder .37
8.3.3 Inspection of the tooth contact pattern .37
8.4 Inspection of the pitch .38
8.4.1 Calculation of pitch .38
8.4.2 Inspection using an automatic device on the cutting machine: inspection
of the single circular pitch and the cumulative pitch deviation .38
8.4.3 Manual inspection: inspection of base pitch, p , and base pitch deviations, f .
b pb 39
8.5 Measuring tooth thickness .39
8.6 Measuring gear radial runout and axial runout of reference surfaces .39
9 Measurement analysis — Profile, helix, pitch and radial runout .39
9.1 Profile .39
9.1.1 Profile deviation .39
9.1.2 Profile deviation diagram .40
9.1.3 Evaluation of profile diagrams .41
9.1.4 Algebraic signs of f , f and f .
Hα b α 42
9.1.5 Mean profile slope deviation, f .
Hαm 42
9.2 Helix.43
9.2.1 General.43
9.2.2 Helix deviation diagram .44
9.2.3 Evaluation of helix diagrams .45
9.2.4 Algebraic signs of f and f .
Hβ β 46
9.2.5 Machine corrections based on mean helix slope deviation, f .
Hβm 47
9.3 Pitch .48
9.3.1 Pitch deviation .48
9.3.2 Pitch deviation measurement .48
9.3.3 Relationships of pitch parameters and measuring methods .48
9.3.4 Calculation of cumulative pitch (index), F .
p 49
9.3.5 Calculation of single pitch, f .
pi 50
9.3.6 Calculation of total cumulative pitch deviation, F .
p 50
9.3.7 Calculation of sector pitch deviation, F .
pk 50
9.3.8 Segment gear measurement .50
9.4 Radial runout, determining eccentricity .51
9.4.1 Measuring principle .51
9.4.2 Evaluation of measurement .51
10 Interpretation of profile, helix, pitch and radial runout results .52
10.1 Interpreting measurement results .52
10.2 Procedure for interpreting measurement results .52
10.3 Recognition of common manufacturing errors.53
10.3.1 General.53
10.3.2 Example of a profile with pressure angle deviation .53
10.3.3 Example of profile deviations with varying pressure angle deviation .53
10.3.4 Hob runout or shaping cutter deflection .54
10.3.5 Consistent mean helix slope deviation .55
10.3.6 Helix slope variation .55
10.3.7 Profile control diameter not achieved .56
10.3.8 Variation in profile non-clean up and profile control diameter not achieved .56
10.3.9 Pitch results with radial runout of the gear blank .58
10.3.10 Pitch with indexing deviations .58
10.3.11 Pitch with repeating deviation patterns that may cause noise .61
11 Single flank composite testing .61
11.1 Single flank composite testing principle .61
11.2 Single flank composite test .62
11.2.1 Single flank test setup . . .62
11.2.2 Single flank composite deviations .64
11.3 Single flank measurement with master gear .65
11.3.1 Master gear requirements .65
11.3.2 Influence of profile deviations .65
11.3.3 Influence of pitch deviations .66
11.3.4 Influence of helix deviations .66
11.4 Single flank measurement of product gear pair .69
11.4.1 Differences between tests with a master gear and between two product gears .69
iv © ISO 2017 – All rights reserved

11.4.2 Identification and location of defects .69
11.4.3 Selective meshing of gears .69
11.5 Data analysis by the Fourier transform method .70
12 Additional measurements .71
12.1 Flank measurements.71
12.1.1 General.71
12.1.2 Twist measurement.71
12.1.3 Topographical measurement .72
12.1.4 Undulations .73
12.2 Surface roughness measurement .74
12.3 Tooth root fillet radius measurement .74
13 Filters and data density .75
13.1 General .75
13.2 Examples of filtered results .75
13.3 Working principle of the Gauss 50 % filter .75
13.4 Filter limitations .81
14 Additional calculations .81
14.1 Calculation of single pitch deviation, f , from normal base pitch measurements .81
pt
14.2 Additional calculations for normal base pitch measurements .82
14.2.1 Included parameters .82
14.2.2 Calculation of normal base pitch deviation, f .
pbn 82
14.2.3 Calculation of mean normal base pitch deviation, f .
pbnm 82
14.3 Additional calculations for profile measurements .82
14.3.1 Included parameters .82
14.3.2 Mean base diameter deviation and mean pressure angle deviation .83
14.3.3 Calculation of effective base diameter, d .
b eff 84
14.3.4 Calculation of effective transverse pressure angle, α .
t eff 84
14.3.5 Calculation of effective normal pressure angle, α . .
n eff 84
14.3.6 Calculation of mean transverse pressure angle deviation, f .
αmt 85
14.3.7 Calculation of mean normal pressure angle deviation, f .
αmn 85
14.4 Additional calculations for helix measurements .85
14.4.1 Included parameters .85
14.4.2 Required preliminary data .86
14.4.3 Calculation of effective helix angle at the measurement diameter, β .
M eff 86
14.4.4 Calculation of effective lead, p .
z eff 86
14.4.5 Calculation of effective helix angle at the standard pitch diameter, β .
eff 87
14.4.6 Calculation of mean lead deviation, f .
pzm 87
14.4.7 Calculation of mean helix angle deviation, f .
βm 87
Bibliography .89
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by ISO/TC 60, Gears.
This second edition cancels and replaces the first edition (ISO/TR 10064-1:1992), which has been
technically revised. It also incorporates the Technical Corrigendum ISO/TR 10064-1:1992/Cor. 1:2006.
The following changes have been made:
— the contents have been updated to correspond with ISO 1328-1:2013;
— additional material has been added on the proper setup and use of measuring machines, and how
the measurement results can be used to determine the corrective steps needed to improve the gear
tooth flank tolerance class.
A list of all parts in the ISO/TR 10064 series can be found on the ISO website.
vi © ISO 2017 – All rights reserved

TECHNICAL REPORT ISO/TR 10064-1:2017(E)
Code of inspection practice —
Part 1:
Measurement of cylindrical gear tooth flanks
1 Scope
This document supplements ISO 1328-1:2013. It provides a code of practice dealing with measurements
on flanks of individual cylindrical involute gears, i.e. with the measurement of pitch, profile, helix
and tangential composite characteristics. It describes measuring equipment, provides advice for gear
measuring methods and for the analysis of measurement results, and discusses the interpretation of
results.
Measurements using a double flank tester are not included (see ISO/TR 10064-2). This document only
applies to involute gears.
2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms, definitions, symbols and abbreviated terms apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
NOTE The symbols and terms used throughout this document are in basic agreement with the symbols and
terms given in ISO 701 and in ISO 1122-1. In all cases, the first time that each symbol is introduced, it is defined
and discussed in detail. See Table 1. Abbreviated terms are given in Table 2.
Table 1 — Symbols and definitions
a
Symbols Definition Units First use
a tip point — Figure 31
b face width mm Figure 37
C profile control point — Figure 31
f
d reference diameter mm Formula (4)
d tip diameter mm 14.3.2.1
a
d effective (measured) tip diameter mm Figure 29
a eff
d base diameter mm Formula (6)
b
d effective base diameter mm 14.2
b eff
a
Symbols used for deviations of individual element measurements from specified values are composed of lower case
letters “ f ” with subscripts (exceptions include f , f and f ) whereas symbols used for “cumulative” or “total” deviations,
e 1 2
which represent combinations of several individual element deviations, are composed of capital letters “F” also with
subscripts. It is necessary to qualify some deviations with an algebraic sign. A deviation is positive when, for example, a
dimension is larger than optimum and negative when smaller than optimum.
b
These deviations can be + (plus) or − (minus).
Table 1 (continued)
a
Symbols Definition Units First use
d measurement diameter mm 6.2.3.2
M
d start of active profile (SAP) diameter mm Formula (8)
Nf
d individual inspection diameter (measurement diameter) mm Figure 29
y
F tip form point (where tip break starts) — Figure 31
a
F total single flank composite deviation μm 11.1
is
F total cumulative pitch deviation μm 9.3.1
p
F individual total cumulative pitch deviation μm 9.3.8
pi
F sector pitch deviation over k pitches μm 9.3.7
pk
F radial runout μm 6.2.5
r
F total profile deviation μm Figure 14
α
F total helix deviation μm Figure 37
β
f difference between the actual and nominal pressure angle degrees 9.1.4
α
f mean pressure angle deviation degrees 14.3.1
αm
base circle deviation (difference between the actual and nominal base
f mm 9.1.4
b
diameter)
f mean base diameter deviation mm 14.3.1
bm
f eccentricity between gear axis and axis of gear teeth μm Figure 34
e
f profile form deviation μm Figure 14
fα
f helix form deviation μm Figure 37
fβ
f helix form tolerance μm 8.3.1
fβΤ
b
f profile slope deviation μm Figure 14
Hα
b
f mean profile slope deviation μm 9.1.5
Hαm
b
f individual profile slope deviation μm 9.1.5
Hαi
b
f helix slope deviation μm 6.4
Hβ
b
f individual helix slope deviation μm 9.2.5
Hβi
b
f mean helix slope deviation μm 9.2.5
Hβm
mean helix slope deviation, in the transverse plane and tangent to the
f μm Formula (37)
Hβmt
b
measurement diameter
tooth-to-tooth single flank composite deviation without removal of the
f μm 11.2.2
i′
long term component
tooth-to-tooth single flank composite deviation after removal of long
f μm 11.1
is
term component
f variance of the long period component over one revolution μm 11.2.2
l′
b
f single pitch deviation μm 8.4.3
p
b
f mean lead deviation mm 14.4.1
pzm
b
f mean normal base pitch deviation μm 14.2.1
pbnm
b
f normal base pitch deviation μm 6.2.4
pbn
b
f individual normal base pitch deviation μm 14.1
pbni
b
f single pitch deviation , normal base μm 8.4.3
pb
b
f single pitch deviation , transverse base μm Formula (19)
pbt
a
Symbols used for deviations of individual element measurements from specified values are composed of lower case
letters “ f ” with subscripts (exceptions include f , f and f ) whereas symbols used for “cumulative” or “total” deviations,
e 1 2
which represent combinations of several individual element deviations, are composed of capital letters “F” also with
subscripts. It is necessary to qualify some deviations with an algebraic sign. A deviation is positive when, for example, a
dimension is larger than optimum and negative when smaller than optimum.
b
These deviations can be + (plus) or − (minus).
2 © ISO 2017 – All rights reserved

Table 1 (continued)
a
Symbols Definition Units First use
b
f individual single pitch deviation μm Figure 42
pi
b
f individual double pitch deviation μm 9.3.8
p2i
b
f individual adjacent pitch difference μm 9.3.8
ui
b
f individual adjacent double pitch difference μm 9.3.8
u2i
f undulation wave height in profile direction μm Figure 74
wα
f undulation wave height in helix direction μm Figure 74
wβ
b
f pressure angle deviation degrees 9.1.4
α
b
f mean normal pressure angle deviation degrees 14.2.1
αmn
b
f mean transverse pressure angle deviation degrees 14.2.1
αmt
b
f helix angle deviation degrees 9.2.4
β
b
f mean helix angle deviation degrees 9.2.4
βm
g length of path of contact mm Figure 65
α
h chordal addendum to an individual measurement diameter mm Figure 29
cy
h radial distance from tip to an individual measurement diameter mm Figure 29
y
k number of pitches in a sector — 5.7
L left flank — 5.3
L profile evaluation length mm Figure 14
α
L functional profile length mm 14.3.2.2
αc
L base tangent length to start of active profile mm Figure 14
αe
L helix evaluation length mm 8.3.1
β
l left hand helix — 5.4
m normal module mm Formula (1)
n
N pitch number — 5.6
N start of active profile point on line of action — Figure 31
f
n number of deviation values included in the mean — 9.1.5
p base pitch mm 8.4.3
b
p normal base pitch mm Formula (1)
bn
p transverse base pitch mm Formula (16)
bt
b
p true position pitch μm 14.1
m
p lead of the helix mm Formula (36)
z
p effective lead mm 14.4.1
z eff
R right flank — 5.3
r right hand helix — 5.4
s undulation weighting factor mm Figure 80
s chordal tooth thickness at an individual inspection diameter mm Figure 29
cy
s normal circular tooth thickness at the reference diameter mm Formula (12)
n
s normal circular tooth thickness at an individual inspection diameter mm Figure 29
yn
z number of teeth — 6.2.3.2
z number of teeth in master indexing worm wheel — Formula (22)
M
a
Symbols used for deviations of individual element measurements from specified values are composed of lower case
letters “ f ” with subscripts (exceptions include f , f and f ) whereas symbols used for “cumulative” or “total” deviations,
e 1 2
which represent combinations of several individual element deviations, are composed of capital letters “F” also with
subscripts. It is necessary to qualify some deviations with an algebraic sign. A deviation is positive when, for example, a
dimension is larger than optimum and negative when smaller than optimum.
b
These deviations can be + (plus) or − (minus).
Table 1 (continued)
a
Symbols Definition Units First use
z number of teeth on driving gear — Figure 61
z number of teeth on driven gear — Figure 61
α Gauss parameter — Formula (24)
50 %
α transverse pressure angle at the measurement diameter degrees 10.3.9
Mt
α normal pressure angle degrees Formula (1)
n
α effective normal pressure angle degrees 14.2.1
n eff
α transverse pressure angle degrees Formula (5)
t
α effective transverse pressure angle degrees 14.2.1
t eff
α normal pressure angle at an individual inspection diameter degrees 8.2.3
yn
α transverse pressure angle at an individual inspection diameter degrees Formula (11)
yt
α transverse pressure angle at measurement diameter degrees 10.3.9
Mt
β helix angle degrees Formula (4)
β base helix angle degrees Formula (17)
b
β effective helix angle at the standard pitch diameter degrees 14.4.1
eff
β effective helix angle at the measurement diameter degrees 14.4.1
M eff
β helix angle at an individual inspection diameter degrees Formula (10)
y
ε total contact ratio — 11.3.4.2
γ
λ undulation wavelength mm Figure 74
g
λ undulation wavelength in profile direction mm Figure 74
α
λ undulation wavelength in helix direction mm Formula (22)
β
ξ involute roll angle degrees Figure 14
ξ involute roll angle to the tip diameter radians Formula (7)
a
ξ involute roll angle to the start of active profile diameter radians Formula (8)
Nf
ξ individual inspection roll angle radians Formula (9)
y
θ angular position of gear radians Figure 61
Δθ angular gear position deviation radians Figure 61
I reference face — 5.3
II non-reference face — 5.3
a
Symbols used for deviations of individual element measurements from specified values are composed of lower case
letters “ f ” with subscripts (exceptions include f , f and f ) whereas symbols used for “cumulative” or “total” deviations,
e 1 2
which represent combinations of several individual element deviations, are composed of capital letters “F” also with
subscripts. It is necessary to qualify some deviations with an algebraic sign. A deviation is positive when, for example, a
dimension is larger than optimum and negative when smaller than optimum.
b
These deviations can be + (plus) or − (minus).
Table 2 — Abbreviated terms
Definition First use
3D three dimensional 6.2.6
CAD computer aided design 6.2.6
CMM coordinate measuring machine 6.1
CNC computer numerically controlled 6.1
CT computer tomography 6.2.6
GCM gear cutting machine 8.3.3
GMM gear measuring machine 6.1
4 © ISO 2017 – All rights reserved

4 General considerations
4.1 Background
The purpose of this document is to provide background information that will assist with understanding
the requirements, implementation and effectiveness of the gear measurements needed to establish the
gear classifications defined in ISO 1328-1. This information will assist those involved in gear design and
specification, gear manufacture and gear measurement processes. It includes background information
and guidance on good measurement practice and addresses the interpretation of measurement results
to identify common causes of gear manufacturing errors. Improved knowledge of gear measurement
processes enhances the value of investments in measuring equipment.
When producing multiple identical gears in a large batch, it is rarely necessary or economical to
measure all possible deviations on all the gears manufactured. Stable manufacturing processes allow
a relatively small number of samples to be measured and still ensure that the required tolerance
class is maintained. Certain elements may not significantly influence the function of the gear under
consideration. However, some gear manufacturing processes are known to increase the risk of
significant variation in tooth geometry in a single gear and thus require additional measurements to
verify gear geometry parameter tolerances have been achieved. Some guidance is provided when this
is necessary, but it remains the responsibility of the manufacturer of the gears to assure that the gears
satisfy the specified requirements, such as those in ISO 1328-1. It is recommended that measuring plans
be agreed upon between the manufacturer and the purchaser.
4.2 Required inspection information
All necessary information should be provided to the operator(s) of the measuring equipment. The
information required will vary depending on the type of measurement(s). Most measurement processes
require basic gear and blank data, such as number of teeth, pressure angle, helix angle, module, tip
diameter, root diameter, face width, design profile, design helix, etc. Certain measuring tasks require
additional information. For example, to measure profile, the profile control diameter and start of tip
break must be provided. Minimum requirements are defined in ISO 1328-1 but it is the responsibility
of the gear designer to ensure the specification provides sufficient information for the manufacturer to
develop a measurement strategy that is suitable for the subject gears.
4.3 Measurement selection
4.3.1 Substitution of measurement methods
Inspection may be carried out using a number of methods. In some cases, some measurements may be
substituted for others. For example, single flank composite measurement may be substituted for pitch
measurement, or radial composite measurement may replace radial runout measurement. However,
such substitutions may only be done with agreement between the manufacturer and the purchaser. See
ISO 1328-1:2013, Table 4.
A number of factors should be considered when selecting the measurements, including the tolerance class
required, size of the gear, manufacturing cost, and most important, the application of the product gear.
4.3.2 First piece inspection
It may be possible to verify that the manufacturing process is correct by inspecting only the first piece
of a batch, allowing the inherent accuracy of the process to assure subsequent parts meet the required
tolerance class.
4.3.3 Sampling and statistical process control
The deviations from the design shape of the gear that result from the manufacturing process are
dependent on the production process used. When the process is proven capable of producing the
required tolerance class (e.g. when using statistical methods), sampling inspection may be utilized.
Many factors may influence the sample size and frequency; foremost among these should be the
assurance that the required tolerance class of the parts is met.
The variability of the measuring process contributes to the perceived variability of the manufacturing
process. For more information, see ISO 22514-7.
To achieve statistical compliance, the manufacturing deviations must be smaller than the specified
tolerance. In some cases, for very accurate gears, the use of statistical process control is not possible
due to the uncertainty in the measurements.
5 Conventions and measurement positions
5.1 General
When measuring gear teeth, specific reference is made to right flanks, left flanks, pitches, teeth or
combinations of these.
5.2 Datum axis
Specification of the design profile, design helix, and design pitch requires definition of an appropriate
reference axis of rotation, called the datum axis. It is defined by specification of datum surfaces. See
ISO/TR 10064-3.
The datum axis is the reference for measurements and associated tolerances. The location and
orientation of the measurement diameter circle are determined by this axis.
Ideally, the surfaces used to construct the datum axis, the surfaces used to locate the gear for
manufacturing, and the functional surfaces that define the gear axis of rotation in its final assembly
will all be the same. In practice, this is often not the case. For example, shaft type parts are often
manufactured and inspected using centres to define the datum axis. In cases where the inspection,
manufacturing, and/or functional datum surfaces are different, these surfaces should be coincident
with each other to a level of accuracy sufficient to assure the final positioning of the gear is adequately
represented during measurement.
When a rotary table is used, the gear being measured should be oriented so that its datum axis is
coincident with the axis of rotation of the measuring instrument. In the case of mounting the gear
between centres, care should be taken to assure that the mounting arbor, if used, is in good condition,
and the centres are clean and concentric with the datum surfaces of the gear. In the case of computer
controlled measuring instruments, if the measuring program is capable of mathematically correcting
the errors resulting fro
...