CMM Verification Best Practice No. 42 Final

A NATIONAL MEASUREMENTGOOD PRACTICE GUIDEA NATIONAL MEASUREMENTGOOD PRACTICE GUIDENo. 42No. 42CMM VerificationCMM Verification

The DTI drives our ambition of‘prosperity for all’ by working tocreate the best environment forbusiness success in the UK.We help people and companiesbecome more productive bypromoting enterprise, innovationand creativity.The DTI drives our ambition of‘prosperity for all’ by working tocreate the best environment forbusiness success in the UK.We help people and companiesbecome more productive bypromoting enterprise, innovationand creativity.We champion UK business at homeand abroad. We invest heavily inworld-class science and technology.We protect the rights of workingpeople and consumers. And westand up for fair and open marketsin the UK, Europe and the world.We champion UK business at homeand abroad. We invest heavily inworld-class science and technology.We protect the rights of workingpeople and consumers. And westand up for fair and open marketsin the UK, Europe and the world.This Guide was developed by the NationalPhysical Laboratory on behalf of the NMS.This Guide was developed by the NationalPhysical Laboratory on behalf of the NMS.

Measurement Good Practice Guide No. 42CMM VerificationDavid FlackDimensional and Optical Metrology TeamCentre for Basic, Thermal and Length MetrologyAbstract: This guide covers performance assessment of CMM accuracy, use of everydayartefacts for regular CMM checking, methods of monitoring machine performancebetween formal verification intervals, and traceablilty.

Crown Copyright 2001Reproduced by permission of the Controller of HMSOJuly 2001ISSN 1368-6550National Physical LaboratoryTeddington, Middlesex, United Kingdom, TW11 0LWAcknowledgementsThe author would like to thank Mr. Alan Hatcher (Mitutoyo Ltd) for supplying much ofthe information given in this guide and Mr. Keith Bevan (Mitutoyo Ltd), Mr. MikeCrossman and Mr John Cubis (UKAS) for providing useful technical input. Thanks also toDr. G N Peggs and Dr. R Angus (NPL) and all lead users who reviewed the various draftsand last but not least the Department of Trade and Industry (DTI) for funding productionof this guide as part of the 1999-2002 Length Programme (Project MPU 8/61.3).

CMM VerificationContents1.INTRODUCTION . 11.1CO-ORDINATE MEASURING MACHINES. 12.SOURCES OF CMM ERROR. 33.ISO 10360-2: 1994 COORDINATE METROLOGY . 44.BASIC TERMINOLOGY . 54.14.25.MATERIAL STANDARD OF LENGTH . 5ERROR OF INDICATION. 6THE ACCEPTANCE TEST . 75.15.25.35.45.5PRELIMINARY. 7CHOICE OF ARTEFACT . 8ACCEPTANCE TEST PROCEDURE. 10CALCULATION OF RESULTS . 12INTERPRETATION OF THE RESULTS . 146.PERIODIC REVERIFICATION. 167.ACCEPTANCE TEST OF THE CMM PROBING SYSTEM. 177.17.27.37.4PROBING ERROR R . 17ACCEPTANCE TEST PROCEDURE. 17CALCULATION OF RESULTS . 18INTERPRETATION OF RESULTS. 198.PERIODIC REVERIFICATION. 219.INTERIM CHECK OF THE CMM . 229.1A PURPOSE MADE TEST PIECE . 229.2A BALL-ENDED BAR . 249.3A BAR THAT CAN BE KINEMATICALLY LOCATED BETWEEN AFIXED REFERENCE SPHERE AND THE SPHERE OF THE CMM PROBESTYLUS . 259.4A CIRCULAR REFERENCE OBJECT (FOR EXAMPLE A RINGGAUGE) . 279.5A BALL PLATE. 289.6A HOLE PLATE. 29

10.INTERIM PROBE CHECKING . 3011.IMPROVING MEASUREMENT CONFIDENCE. 3112.CMMS USING MULTIPLE STYLUS PROBING SYSTEMS. 3413. ASSESSMENT AND REVERIFICATION TESTS FOR CMMS WITH THEAXIS OF A ROTARY TABLE AS THE FOURTH AXIS . 3513.113.2REQUIREMENTS . 3513.1.1 Error of indication . 3513.1.2 Environmental conditions . 3513.1.3 Stylus system. 3613.1.4 Operating conditions . 36ACCEPTANCE AND REVERIFICATION TESTS. 3613.2.1 Principles . 3613.2.2 Measuring equipment. 3713.2.3 Set up and procedure. 3713.2.4 Results . 4013.2.5 Compliance with specifications. 4014.VERIFICATION OF LARGE CMMS . 4115.SUMMARY . 4216.GLOSSARY OF TERMS. 4317.HEALTH AND SAFETY . 46APPENDIX A LINKS TO OTHER USEFUL SOURCES OF INFORMATION . 47A.1A.2A.3A.4A.5NATIONAL AND INTERNATIONAL ORGANISATIONS . 47A.1.1 National Physical Laboratory . 47A.1.2 National Institute of Science and Technology (NIST). 47A.1.3 EUROMET. 47A.1.4 European Co-operation for Accreditation (EA). 48CLUBS . 49A.2.1 Dimensional Metrology Awareness Club (DMAC) . 49A.2.2 Software Support for Metrology Programme (SSfM) . 49NATIONAL AND INTERNATIONAL STANDARDS. 50A.3.1 British Standards Institution (BSI) . 50A.3.2 International Organisation for Standardisation (ISO). 50TRACEABILITY. 51NATIONAL MEASUREMENT PARTNERSHIP (NMP). 53

A.6A.7A.8A.9TRAINING COURSES . 54AWARDING BODIES. 55MANUFACTURERS . 55FURTHER READING . 56List of FiguresFigure 1 A step gauge on a CMM . 5Figure 2 Gauge blocks and end bars . 6Figure 3 Gauge blocks on a CMM . 8Figure 4 Example measuring lines . 11Figure 5 Position and orientation of gauge blocks . 11Figure 6 Graphical representation of ISO 10360 test. 15Figure 7 Example probe test . 20Figure 8 A purpose made test piece . 23Figure 9 A test piece ( SIP) . 24Figure 10 Ball Bars ( Bal-tec) . 24Figure 11 Free Standing ball Bar Kit ( Bal-Tec) . 24Figure 12 An example of a ball-ended rod with magnetic cups for kinematic location. 25Figure 13 Renishaw machine checking gauge ( Renishaw) . 26Figure 14 Machine checking gauge – ( Renishaw) . 26Figure 15 Machine checking gauge envelope ( Renishaw) . 27Figure 16 A ring gauge checking a CMM. 28Figure 17 A Ball Plate . 29Figure 18 A Hole plate. 29Figure 19 Reference artefact (ring gauge). 31Figure 20 Component – a long tube . 32List of tablesTable 1 Comparison of various material standards of length . 9Table 2 Example of acceptance test results and computations. 13Table 3 Typical sphere test data. 19Table 4 Location of the test spheres on the rotary table . 37Table 5 Default nominal angular positions for rotary table test . 39

MEASUREMENT GOOD PRACTICEThere are six guiding principles to good measurement practice that have been defined byNPL. They areThe Right Measurements: Measurements should only be made to satisfy agreed and wellspecified requirements.The Right Tools: Measurements should be made using equipment and methods that have beendemonstrated to be fit for purpose.The Right People: Measurement staff should be competent, properly qualified and well informed.Regular review: There should be both internal and independent assessment of the technicalperformance of all measurement facilities and procedures.Demonstratable Consistency: Measurements made in one location should be consistent withthose made elsewhereThe Right Procedures: Well-defined procedures consistent with national or internationalstandards should be in place for all measurements

Measurement Good Practice Guide No. 421. INTRODUCTION1.1 CO-ORDINATE MEASURING MACHINESInternational Standard ISO 10360-1 defines a Co-ordinate Measuring Machine (CMM) as ameasuring system with the means to move a probing system and capability to determinespatial coordinates on a workpice surface. Over the years standards and guidelines havebeen developed to harmonize the performance specifications of a CMM to enable a user tomake meaningful performance comparisons when purchasing a machine and, oncepurchased, to provide a well-defined way in which the specified performance can beverified.For the user, demonstrating traceability to national standards and estimating the accuracyof measurements made with three dimensional CMMs is of extreme importance formaintaining confidence and reliability in the measurements.The ISO 10360 series of standards detail the acceptance, reverification tests and interimchecks required to determine whether the CMM performs to the manufacturer’s statederror of indication. However even with these tests it is not possible to make a statementabout the length measurement capability of the machine due to the complicated way inwhich the uncertainties associated with the CMM combine. Therefore, the lengthmeasurement uncertainty derived from a limited sample of measurements cannot beconsidered to be representative of all the possible length measurement tasks and certainlynot of the measurement tasks the CMM is capable of performing. In effect the tests do notguarantee traceability of measurement for all measurement tasks performed. The usershould be aware of this important fact and develop task-related measuring strategies foreach measurement undertaken that will provide the appropriate level of confidence in theoverall result. Virtual CMMs can meet this requirement. Further information on virtualCMMs can be found in NPL report CMSC 01/00 Simulated Instruments and UncertaintyEstimation A B Forbes and P M Harris.International Standard ISO 10360 covers CMM verification. This standard has five parts: ISO 10360-1:2000 Geometrical Product Specifications (GPS) – Acceptance andreverification tests for coordinate measuring machines (CMM)—Part 1: Vocabulary1

Measurement Good Practice Guide No. 42 ISO 10360-2:1994 Coordinate Metrology—Part 2: Performance assessment ofcoordinate measuring machines ISO 10360-3:2000 Geometrical Product Specifications (GPS) – Acceptance andreverification tests for coordinate measuring machines (CMM)—Part 3: CMMs withthe axis of a rotary table as the fourth axis ISO 10360-4:2000 Geometrical Product Specifications (GPS) – Acceptance andreverification tests for coordinate measuring machines (CMM)—Part 4: CMMs usedis scanning measuring mode ISO 10360-5:2000 Geometrical Product Specifications (GPS) – Acceptance andreverification tests for coordinate measuring machines (CMM)—Part 5: CMMsusing multiple-stylus probing systemsThis guide will concentrate on the tests listed in part 2 of the standard and will cover someaspects of parts 3 and 5. It will also give some guidance on techniques available for largerCMMs not covered by the above specification.Note:This good practice guide is based on the specifications as listed above. However for some time ISOTC213/WG10 has been undertaking a short-term revision of ISO 10360-2 so that it conforms toother parts of the ISO 10360 series. A longer term revision of ISO 10360-2 is in the process ofdiscussion but it will be some time before this will supersede the short-term revision of thestandard.The new title for this part of the standard is expected to be: Geometrical Product Specifications(GPS) – Acceptance test and reverification test for coordinate measuring machines (CMM)-Part 2:CMM’s used for measuring size.It is suggested that the reader regularly checks the catalogue on the ISO web site for furtherinformation.2