The Gauge Block Handbook - NIST

1 IiiThe Gauge Block HandbookbyTed Doiron and John BeersDimensional Metrology GroupPrecision Engineering DivisionNational Institute of Standards and TechnologyPrefaceThe Dimensional Metrology Group, and its predecessors at the National Institute of Standardsand Technology (formerly the National Bureau of Standards) have been involved indocumenting the science of Gauge Block calibration almost continuously since the seminal workof Peters and Boyd in 1926 [1]. Unfortunately, most of this documentation has been in the formof reports and other internal documents that are difficult for the interested metrologist outside theInstitute to obtain. On the occasion of the latest major revision of our calibration procedures we decided to assembleand extend the existing documentation of the NIST Gauge Block calibration program into onedocument.

2 We use the word assemble rather than write because most of the techniques describedhave been documented by various members of the Dimensional Metrology Group over the last 20years. Unfortunately, much of the work is spread over multiple documents, many of the detailsof the measurement process have changed since the publications were written, and many largegaps in coverage exist. It is our hope that this Handbook has assembled the best of the previousdocumentation and extended the coverage to completely describe the current Gauge blockcalibration of the sections are based on previous documents since very little could be added incoverage. In particular, the entire discussion of single wavelength interferometry is due to JohnBeers [2]; the section on preparation of Gauge blocks is due to Clyde Tucker [3]; the section onthe mechanical comparator techniques is predominantly from Beers and Tucker [4]; and theappendix on drift eliminating designs is an adaptation for dimensional calibrations of the work ofJoseph Cameron [5] on weighing designs.

3 They have, however, been rewritten to make thehandbook consistent in style and coverage. The measurement assurance program has beenextensively modified over the last 10 years by one of the authors (TD), and chapter 4 reflectsthese changes. ivWe would like to thank Mr. Ralph Veale, Mr. John Stoup, Mrs. Trish Snoots, Mr. Eric Stanfield,Mr. Dennis Everett, Mr. Jay Zimmerman, Ms. Kelly Warfield and Dr. Jack Stone, the membersof the Dimensional Metrology Group who have assisted in both the development and testing ofthe current Gauge Block calibration system and the production of this document. TD and JSBvCONTENTS PagePreface.

4 IiiIntroduction ..11. The meter .. The inch .. 32. Gauge A short history of Gauge blocks .. Gauge Block standards ( ).. Scope .. Nomenclature and definitions .. Tolerance grades .. Recalibration requirements .. standards .. 103. Physical and thermal properties of Gauge Materials .. and Flatness measurement .. Parallelism measurement .. Thermal expansion .. expansion of Gauge Block materials .. Thermal expansion uncertainty .. Elastic properties .. Contact deformation in mechanical comparisons .. Measurement of probe force and tip radius .. Stability .. 30vi4. Measurement assurance .. A comparison: traditional metrology vs measurement assurance Tradition.

5 Process control: a paradigm shift .. Measurement assurance: building a measurement process model .. Determining Uncertainty Stability .. Uncertainty .. Random error .. Systematic error and type B uncertainty .. Error budgets .. Combining type A and type B uncertainties .. Combining random and systematic errors .. The NIST Gauge Block measurement assurance program Establishing interferometric master values .. The comparison process .. Measurement schemes - drift eliminating designs .. Control parameter for repeatability .. Control test for variance .. Control parameter (S-C).. Control test for (S-C), the check standard.

6 Control test for drift .. Calculating total uncertainty .. Summary of the NIST measurement assurance program ..66vii5. The NIST mechanical comparison procedure .. Preparation and inspection .. Cleaning procedures .. Cleaning interval .. Storage .. Deburring Gauge blocks .. The comparative principle .. Examples .. Gauge Block comparators .. Scale and contact force control .. Stylus force and penetration corrections .. Environmental factors .. Temperature effects .. Control of temperature effects .. procedures .. Handling techniques .. Comparison designs .. Drift eliminating designs .. The 12/4 design.

7 The 6/3 design .. The 8/4 design .. The ABBA design .. Example of calibration output using the 12/4 design .. Current NIST system performance .. Summary ..916. Gauge Block Introduction .. Interferometers .. The Kosters type interferometer .. The NPL interferometer .. Testing optical quality of interferometers .. Interferometer corrections .. Laser light sources .. Environmental conditions and their measurement .. Temperature .. Atmospheric pressure .. Water vapor .. Gauge Block measurement procedure .. Computation of Gauge Block length .. Calculation of the wavelength .. Calculation of the whole number of fringes.

8 Calculation of the Block length from observed data .. Type A and B errors .. Process evaluation .. Multiple wavelength interferometry .. Use of the line scale interferometer for end standard calibration .. 1177. References ..120 Appendix A. Drift eliminating designs for non-simultaneous comparison calibrations .. 124 Appendix B. Wringing films .. 138 Appendix C. Phase shifts in Gauge Block interferometry .. 141 Appendix D. Deformation corrections .. 146 viii1 Gauge Block HandbookIntroductionGauge Block calibration is one of the oldest high precision calibrations made in dimensionalmetrology. Since their invention at the turn of the century Gauge blocks have been the majorsource of length standardization for industry.

9 In most measurements of such enduringimportance it is to be expected that the measurement would become much more accurate andsophisticated over 80 years of development. Because of the extreme simplicity of Gauge blocksthis has only been partly true. The most accurate measurements of Gauge blocks have notchanged appreciably in accuracy in the last 70 years. What has changed is the much morewidespread necessity of such accuracy. Measurements, which previously could only be madewith the equipment and expertise of a national metrology laboratory, are routinely expected inprivate industrial meet this widespread need for higher accuracy, the calibration methods used for Gauge blockshave been continuously upgraded.

10 This Handbook is a both a description of the current practiceat the National Institute of Standards and Technology, and a compilation of the theory and lore ofgauge Block calibration. Most of the chapters are nearly self-contained so that the interestedreader can, for example, get information on the cleaning and handling of Gauge blocks withouthaving to read the chapters on measurement schemes or process control, etc. This partitioning ofthe material has led to some unavoidable repetition of material between basic structure of the Handbook is from the theoretical to the practical. Chapter 1 concernsthe basic concepts and definitions of length and units. Chapter 2 contains a short history ofgauge blocks, appropriate definitions and a discussion of pertinent national and internationalstandards.