NISI PUBLICATIONS

NIST SPECIAL PUBLICATION 260-120

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DEPARTMENT OF COMMERCE/Technology Administration

National Institute of Standards and Technology

Standard Reference Materials:

A Users' Guide to NIST SRM 2084:

CMM Probe Performance Standard

G. W. Caskey, 8. D. Phillips, B. R. Borchardt,

D. E. Ward, and D. 8. Sawyer
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^At Boulder. CO 80303. ^Some elements at Boulder, CO 80303.
NIST Special Publication 260-120

Standard Reference Materials:

A Users' Guide to NIST SRM 2084:

CMM Probe Performance Standard

G. W. Caskey

S. D. Phillips B. R. Borchardt

D. E. Ward

D. S. Sawyer

Precision Engineering Division National Institute of Standards and Technology

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, Ronald H. Brown, Secretary

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arati Prabhakar, Director Issued June 1994
National Institute of Standards and Technology Special Publication 260-120

Natl. Inst. Stand. Technol. Spec. Publ. 260-120, 28 pages (June 1994)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1994

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
Preface

Standard Reference Materials (SRM's) as defined by the National Institute of Standards and Technology (NIST) are well-characterized materials, produced in quantity and certified for one or more physical or chemical properties. They are used to assure the accuracy and compatibility of measurements throughout the

Nation. SRM's are widely used as primary standards in many diverse fields in science, industry, and technology, both within the United States and throughout

the world. They are also used extensively in the fields of environmental and clinical analysis. In many applications, traceability of quality control and measurement processes to the national measurement system is carried out through

the mechanism and use of SRM's. For many of the Nation's scientists and technologists, it is therefore of more than passing interest to know the details

of the measurements made at NIST in arriving at the certified values of the SRM's

produced. The NIST Special Publication 260 Series is a series of papers reserved

for this purpose.

The 260 Series is dedicated to the dissemination of information on different

phases of the preparation, measurement, certification, and use of NIST SRM's.

In general, much more detail will be found in these papers than is generally

allowed, or desirable, in scientific journal articles. This enables the user to assess the validity and accuracy of the measurement processes employed, to judge

the statistical analysis, and to learn details of techniques and methods utilized

for work entailing greatest care and accuracy. These papers also should provide

sufficient additional information so SRM's can be utilized in new applications

in diverse fields not foreseen at the time the SRM was originally issued. Inquiries concerning the technical content of this paper should be directed to the author(s). Other questions concerned with the availability, delivery, price,

and so forth, will receive prompt attention from: Standard Reference Materials Program

Bldg. 202, Rm. 204 National Institute of Standards and Technology

Gaithersburg, MD 20899

Thomas E. Gills, Chief Standard Reference Materials Program
OTHER NIST PUBLICATIONS IN THIS SERIES

Trahey, N.M., ed., NIST Standard Reference Materials Catalog 1992-93, NIST Spec. Publ. 260 (February

1992). SN003-003-03 146-1*

Michaelis, R.E., and Wyman, L.L., Standard Reference

Materials: Preparation of White Cast Iron Spectro- chemical Standards, NBS Misc. Publ. 260-1 (June

1964). COM74-11061**

Michaelis, R.E., Wyman, L.L., and Flitsch, R., Standard Reference Materials: Preparation of NBS

Copper-Base Spectrochemical Standards, NBS Misc.

Publ. 260-2 (October 1964). COM74-1 1063**

Michaelis, R.E., Yakowitz, H., and Moore, G.A.,

Standard Reference Materials: Metallographic Characterization of an NBS Spectrometric Low-Alloy

Steel Standard, NBS Misc. Publ. 260-3 (October

1964) . COM74-11060**

Hague, J.L., Mears, T.W., and Michaelis, R.E., Standard Reference Materials: Sources of

Information, Publ. 260-4 (February 1965). COM74-

11059**

Alvarez, R., and Flitsch, R., Standard Reference

Materials: Accuracy of Solution X-Ray Spectrometric Analysis of Copper-Base Alloys, NBS Misc. Publ. 260-5 (February 1965). PB 168068**

Shultz, J.I., Standard Reference Materials: Methods for the Chemical Analysis of White Cast Iron Standards, NBS Misc. Publ. 260-6 (July 1965). COM74-

11068**

Bell, R.K., Standard Reference Materials: Methods for the Chemical Analysis of NBS Copper-Base Spectro- chemical Standards, NBS Misc. Publ. 260-7 (October

1965) . COM74-11067**

Richmond, M.S., Standard Reference Materials: Analysis

of Uranium Concentrates at the National Bureau of

Standards, NBS Misc. Publ. 260-8 (December 1965). COM74-11066**

Anspach, S.C., Cavallo, L.M., Garfmkel, S.B., et al., Standard Reference Materials: Half Lives of Materials Used in the Preparation of Standard Reference

Materials of Nineteen Radioactive Nuclides Issued by

the National Bureau of Standards, NBS Misc. Publ. 260-9 (November 1965). COM74-1 1065**

Yakowitz, H., Vieth, D.L., Heinrich, K.F.J. , et al.. Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards II: Cartridge Brass and Low-Alloy Steel, NBS Misc.

Publ. 260-10 (December 1965). COM74-1 1064**

Napolitano, A., and Hawkins, E.G., Standard Reference

Materials: Viscosity of Standard Lead-Silica Glass, NBS Misc. Publ. 260-11** (November 1966).

Yakowitz, H., Vieth, D.L., and Michaelis, R.E., Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards III: White

Cast Iron and Stainless Steel Powder Compact, NBS

Misc. Publ. 260-12 (September 1966). Spijkerman, J.J., Snediker, D.K., Ruegg, F.C., et al.. Standard Reference Materials: Mossbauer

Spectroscopy Standard for the Chemical Shift of Iron Compounds, NBS Misc. Publ. 260-13** (July 1967). Menis, O., and Sterling, J.T., Standard Reference

Materials: Determination of Oxygen in Ferrous Materials (SRMs 1090, 1091, 1092), NBS Misc. Publ. 260-14** (September 1966).

Passaglia, E. and Shouse, P.J., Standard Reference

Materials: Recommended Method of Use of Standard

Ligh-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Testiles for Colorfastness to Light, NBS Spec. Publ. 260-15 (July 1967). Superseded by SP 260-41. Yakowitz, H., Michaelis, R.E., and Vieth, D.L.,

Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of W-20% Mo Alloy Fabricated by Powder Metallurgical Methods, NBS Spec. Publ. 260-16 (January 1969). COM74- 11062**

Catanzaro, E.J., Champion, C.E., Gamer, E.L., et al.. Standard Reference Materials: Boric Acid; Isotopic, and Assay Standard Reference Materials, NBS Spec.

Publ. 260-17 (February 1970). PB 189457**

Geller, S.B., Mantek, P. A., and Cleveland, N.G.,

Calibration of NBS Secondary Standards Magnetic Tape Computer Amplitude Reference Amplitude Measurement "Process A", NBS Spec. Publ. 260-18 (November 1969). Superseded by SP 260-29.

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements

on the Vapor Pressure of Gold (Certification of SRM

745). NBS Spec. Publ. 260-19 (January 1970). PB 190071**

260-20: Unassigned

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements

on the Vapor Pressures of Cadmium and Silver, NBS

Spec. Publ. 260-21 (January 1971). COM74-1 1359**

Yakowitz, H., Fiori, C.E., and Michaelis, R.E.,

Standard Reference Materials: Homogeneity Characterization of Fe-3 Si Alloy, NBS Spec. Publ. 260-22

(February 1971). COM74-1 1357**

iv
Napolitano, A., and Hawkins, E.G., Standard Reference

Materials: Viscosity of a Standard Borosilicate Glass, NBS Spec. Publ. 260-23 (December 1970). COM71-00157**

Sappenfield, K.M., Marinenko, G., and Hague, J.L., Standard Reference Materials: Comparison of Redox

Standards, NBS Spec. Publ. 260-24 (January 1972). COM72-50058**

Hicho, G.E., Yakowitz, H., Rasberry, S.D., et al., Standard Reference Materials: A Standard Reference

Material Containing Nominally Four Percent

Austenite, NBS Spec. Publ. 260-25 (February 1971). COM74-11356**

Martin, J.F., Standard Reference Materials: NBS-U.S.

Steel Corp. Joint Program for Determining Oxygen

and Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). PB 81176620** Gamer, E.L., Machlan, L.A., and Shields, W.R.,

Standard Reference Materials: Uranium Isotopic Standard Reference Materials, NBS Spec. Publ. 260-27 (Apnl 1971). COM74-1 1358**

Heinrich, K.F.J. , Myklebust, R.L., Rasberry, S.D., et

al.. Standard Reference Materials: Preparation and

Evaluation of SRMs 481 and 482 Gold-Silver and Gold-Copper Alloys for Microanalysis, NBS Spec.

Publ. 260-28 (August 1971). C0M7 1-50365**

Geller, S.B., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape

Amplitude Measurement "Process A-Model 2," NBS

Spec. Publ. 260-29 (June 1971). COM71-50282**

Supersedes Measurement System in SP 260-18. Gorozhanina, R.S., Freedman, A.Y., and Shaievitch, A.B., (translated by M.C. Selby), Standard Reference Materials: Standard Samples Issued in the USSR (A Translation from the Russian), NBS Spec.

Publ. 260-30 (June 1971). COM7 1-50283**

Hust, J.G., and Sparks, L.L., Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, NBS Spec. Publ. 260-31 (November 1971). COM7 1-50563**

Mavrodineanu, R., and Lazar, J.W., Standard Reference

Materials: Standard Quartz Cuvettes for High Accuracy Spectrophotometry, NBS Spec. Publ. 260-32 (December 1973). COM74-50018**

Wagner, H.L., Standard Reference Materials: Comparison of Original and Supplemental SRM 705, Narrow

Molecular Weight Distribution Polystyrene, NBS

Spec. Publ. 260-33 (May 1972). COM72-50526**

Sparks, L.L., and Hust, J.G., Standard Reference

Material: Thermoelectric Voltage of Silver-28 Atomic

Percent Gold Thermocouple Wire, SRM 733, Verses Common Thermocouple Materials (Between Liquid Helium and Ice Fixed Points), NBS Spec. Publ. 260- 34 (April 1972). COM72-50371**

Sparks, L.L., and Hust, J.G., Standard Reference

Materials: Thermal Conductivity of Austenitic

Stainless Steel, SRM 735 from 5 to 280 K, NBS

Spec. Publ. 260-35 (April 1972). COM72-50368**

Cali, J. P., Mandel, J., Moore, L.J., et al.. Standard Reference Materials: A Reference Method for the Determination of Calcium in Serum NBS SRM 915, NBS Spec. Publ. 260-36 (May 1972). COM72-50527**

Shultz, J.I., Bell, R.K., Rains, T.C., et al.. Standard Reference Materials: Methods of Analysis of NBS

Clay Standards, NBS Spec. Publ. 260-37 (June

1972). COM72-50692**

Richard, J.C., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of Standards of Spectral Specular Reflectance, NBS Spec. Publ. 260-38 (May 1972). COM72-50528**

Clark, A.F., Denson, V.A., Hust, J.G., et al.. Standard Reference Materials: The Eddy Current Decay Method for Resistivity Characterization of

High-Purity Metals, NBS Spec. Publ. 260-39 (May

1972). COM72-50529**

McAdie, H.G., Gam, P.D., and Menis, O., Standard Reference Materials: Selection of Differential Thermal Analysis Temperature Standards Through a Cooperative Study (SRMs 758, 759, 760), NBS Spec.

Publ. 260-40 (August 1972) COM72-50776**

Wood. L.A., and Shouse, P.J., Standard Reference

Materials: Use of Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Spec. Publ. 260-41 (August 1972). COM72-50775**

Wagner, H.L., and Verdier, P.H., eds.. Standard Reference Materials: The Characterization of Linear

Polyethylene, SRM 1475, NBS Spec. Publ. 260-42

(September 1972). COM72-50944**

Yakowitz, H., Ruff, A.W., and Michaelis, R.E., Standard Reference Materials: Preparation and Homogeneity Characterization of an Austenitic Iron-Chromium-Nickel Alloy, NBS Spec. Publ. 260-43 (November 1972). COM73-50760**

Schooley, J.F., Soulen, R.J., Jr., and Evans, G.A., Jr., Standard Reference Materials: Preparation and Use of

Superconductive Fixed Point Devices, SRM 767, NBS Spec. Publ. 260-44 (December 1972). COM73-50037**

V
Greifer, B., Maienthal, E.J., Rains, T.C., et al., Standard Reference Materials: Development of NBS SRM 1579 Powdered Lead-Based Paint, NBS Spec.

Publ. 260-45 (March 1973). COM73-50226**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Austenitic

Stainless Steel, SRMs 735 and 798, from 4 to 1200

K, NBS Spec. Publ. 260-46 (March 1975). COM75-10339**

Hust, J.G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and

Austenitic Stainless Steel, SRM 798, from 5 to 280

K, NBS Spec. Publ. 260-47 (February 1974). COM74-50176**

Mangum, B.W., and Wise, J. A., Standard Reference

Materials: Description and Use of Precision Thermometers for the Clinical Laboratory, SRM 933 and SRM 934, NBS Spec. Publ. 260-48 (May 1974). Superseded by NIST Spec. Publ. 260-113. COM74-

50533**

Carpenter, B.S., and Reimer, G.M., Standard Reference

Materials: Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260-49 (November

1974). COM74-51185**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Electrolytic Iron, SRMs 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). COM75-10698**

Mavrodineanu, R., and Baldwin, J.R., Standard Reference Matenals: Glass Filters As a SRM for Spectro photometry-Selection, Preparation,

Certification, and Use-SRM 930 NBS Spec. Publ. 260-51 (November 1975). COM75- 10339**

Hust, J.G., and Giarratano, P.J., Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity SRMs 730 and 799, from 4 to 3000 K, NBS Spec. Publ. 260-52 (September 1975). COM75-11193**

Durst, R.A., Standard Reference Materials: Standardization of pH Measurements, NBS Spec. Publ. 260- 53 (December 1978). Superseded by SP 260-53 Rev. 1988 Edition. PB88217427**

Burke, R.W., and Mavrodineanu, R., Standard Reference

Materials: Certification and Use of Acidic Potassium Dichromate Solutions as an Ultraviolet Absorbance

Standard, NBS Spec. Publ. 260-54 (August 1977). PB272168**

Ditmars, D.A., Cezairliyan, A., Ishihara, S., et al.. Standard Reference Materials: Enthalpy and Heat

Capacity; Molybdenum SRM 781, from 273 to 2800

K, NBS Spec. Publ. 260-55 (September 1977). PB272127**

Powell, R.L., Sparks, L.L., and Hust, J.G., Standard Reference Materials: Standard Thermocouple

Material, Pt-67: SRM 1967, NBS Spec. Publ. 260-56

(February 1978). PB277172**

Cali, J. P., and Plebanski, T., Standard Reference

Materials: Guide to United States Reference

Materials, NBS Spec. Publ. 260-57 (February 1978). PB277173**

Barnes, J.D., and Martin, G.M., Standard Reference

Materials: Polyester Film for Oxygen Gas Transmission Measurements SRM 1470, NBS Spec. Publ. 260-58 (June 1979). PB297098**

Chang, T., and Kahn, A.H., Standard Reference

Materials: Electron Paramagnetic Resonance Intensity Standard: SRM 2601; Description and Use, NBS

Spec. Publ. 260-59 (August 1978). PB292097**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al.. Standard Reference Materials: A Reference Method

for the Determination of Sodium in Serum, NBS

Spec. Publ. 260-60 (August 1978). PB286944**

Verdier, P.H., and Wagner, H.L., Standard Reference

Materials: The Characterization of Linear Polyethylene (SRMs 1482, 1483, 1484), NBS Spec. Publ. 260-61 (December 1978). PB289899**

Soulen, R.J., and Dove, R.B., Standard Reference

Materials: Temperature Reference Standard for Use

Below 0.5 K (SRM 768), NBS Spec. Publ. 260-62

(April 1979). PB294245**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al.. Standard Reference Materials: A Reference Method

for the Determination of Potassium in Serum, NBS

Spec. Publ. 260-63 (May 1979). PB297207**

Velapoldi, R.A., and Mielenz. K.D., Standard Reference

Materials: A Fluorescence SRM Quinine Sulfate Dihydrate (SRM 936), NBS Spec. Publ. 260-64

(January 1980). PB80 132046**

Marinenko, R.B., Heinrich, K.F.J. , and Ruegg, F.C., Standard Reference Materials: Micro-Homogeneity

Studies of NBS SRM, NBS Research Materials, and

Other Related Samples, NBS Spec. Publ. 260-65

(September 1979). PB300461**

Venable, W.H., Jr., and Eckerle, K.L., Standard Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of Spectro- photometers (SRMs 2009, 2010, 2013, 2014). NBS

Spec. Publ. 260-66 (October 1979). PB80104961**

vi
Velapoldi, R.A., Paule, R.C., Schaffer, R., et al., Standard Reference Materials: A Reference Method

for the Determination of Chloride in Serum, NBS

Spec. Publ. 260-67 (November 1979). PB801 101 17** Mavrodineanu, R., and Baldwin, J.R., Standard Reference Materials: Metal-On-Quartz Filters as a SRM for Spectrophotometry SRM 2031, NBS Spec. Publ. 260-68 (April 1980). PB80197486**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al., Standard Reference Materials: A Reference Method

for the Determination of Lithium in Serum, NBS

Spec. Publ. 260-69 (July 1980). PB802091I7**

Marinenko, R.B., Biancaniello, F., Boyer, P. A., et al.. Standard Reference Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis: SRM 479a, NBS Spec. Publ. 260-70 (May 1981). SN003-003-02328-1*

Seward, R.W., and Mavrodineanu, R., Standard Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National Bureau

of Standards, NBS Spec. Publ. 260-71 (November

1981). PB82135161**

Reeder, D.J., Coxon, B., Enagonio, D., et al.. Standard Reference Materials: SRM 900, Anti-epilepsy Drug

Level Assay Standard, NBS Spec. Publ. ,260-72 (June

1981). PB81220758

Interrante, C.G., and Hicho, G.E., Standard Reference

Materials: A Standard Reference Material Containing Nominally Fifteen Percent Austenite (SRM 486), NBS Spec. Publ. 260-73 (January 1982). PB82215559**

Marinenko, R.B., Standard Reference Materials: Preparation and Characterization of K-4I1 and K-4I2

Mineral Glasses for Microanalysis: SRM 470, NBS

Spec. Publ. 260-74 (April 1982). PB82221300**

Weidner, V.R., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance Standards (SRM 2003a), NBS Spec. Publ. 260-75 (May 1982). PB82221367**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A Standard Reference Material Containing Nominally Five Percent Austenite (SRM 485a), NBS

Spec. Publ. 260-76 (August 1982). PB83 115568**

Furukawa, G.T., Riddle, J.L., Bigge, W.G., et al.. Standard Reference Materials: Application of Some

Metal SRMs as Thermometric Fixed Points, NBS

Spec. Publ. 260-77 (August 1982). PB83 117325**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: Standard Reference Material Containing Nominally Thirty Percent Austenite (SRM 487), NBS

Spec. Publ. 260-78 (September 1982). PB83 1 15576**

Richmond, J.C., Hsia, J.J., Weidner, V.R., et al.. Standard Reference Materials: Second Surface Mirror

Standards of Specular Spectral Reflectance (SRMs

2023, 2024, 2025), NBS Spec. Publ. 260-79 (October

1982). PB84203447**

Schaffer, R., Mandel, J., Sun, T., et al.. Standard Reference Materials: Evaluation by an ID/MS

Method of the AACC Reference Method for Serum

Glucose, NBS Spec. Publ. 260-80 (October 1982). PB84216894**

Burke, R.W., and Mavrodineanu, R., Standard Reference

Materials: Accuracy in Analytical Spectrophotometry, NBS Spec. Publ. 260-81 (April 1983). PB83214536**

Weidner, V.R., Standard Reference Materials: White

Opal Glass Diffuse Spectral Reflectance Standards for the Visible Spectrum (SRMs 2015 and 2016), NBS

Spec. Publ. 260-82 (April 1983). PB83220723**

Bowers, G.N., Jr., Alvarez, R., Cali, J. P., et al.. Standard Reference Materials: The Measurement of

the Catalytic (Activity) Concentration of Seven Enzymes in NBS Human Serum (SRM 909), NBS

Spec. Publ. 260-83 (June 1983). PB83239509**

Gills, T.E., Seward, R.W., Collins, R.J., et al.. Standard Reference Materials: Sampling, Materials Handling, Processing, and Packaging of NBS Sulfur

in Coal SRMs 2682, 2683, 2684, and 2685, NBS

Spec. Publ. 260-84 (August 1983). PB84109552**

Swyt, D.A., Standard Reference Materials: A Look at Techniques for the Dimensional Calibration of

Standard Microscopic Particles, NBS Spec. Publ. 260-85 (September 1983). PB841 12648**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A SRM Containing Two and One-Half

Percent Austenite, SRM 488, NBS Spec. Publ. 260-86 (December 1983). PB84 143296** Mangum, B.W., Standard Reference Materials: SRM

1969: Rubidium Triple-Point - A Temperature

Reference Standard Near 39.30° C, NBS Spec. Publ. 260-87 (December 1983). PB84149996**

Gladney, E.S., Bums, C.E., Perrin, D.R., et al.. Standard Reference Materials: 1982 Compilation of

Elemental Concentration Data for NBS Biological, Geological, and Environmental Standard Reference

Materials, NBS Spec. Publ. 260-88 (March 1984). PB84218338**

Hust, J.G., Standard Reference Materials: A Fine- Grained, Isotropic Graphite for Use as NBS

Thermophysical Property RMs from 5 to 2500 K, NBS Spec. Publ. 260-89 (September 1984). PB85 112886**

vii
Hust, J.G., and Lankford, A.B., Standard Reference

Materials: Update of Thermal Conductivity and

Electrical Resistivity of Electrolytic Iron, Tungsten, and Stainless Steel, NBS Spec. Publ. 260-90

(September 1984). PB851 15814**

Goodrich, L.F., Vecchia, D.F., Pittman, E.S., et al.. Standard Reference Materials: Critical Current Measurements on an NbTi Superconducting Wire SRM, NBS Spec. Publ. 260-91 (September 1984). PB85118594**

Carpenter, B.S., Standard Reference Materials: Calibrated Glass Standards for Fission Track Use

(Supplement to NBS Spec. Publ. 260-49), NBS Spec.

Publ. 260-92 (September 1984). PB851 13025**

Ehrstein, J.R., Standard Reference Materials: Preparation and Certification of SRM for Calibration of Spreading Resistance Probes, NBS Spec. Publ. 260-93 (January 1985). PB85 177921**

Gills, T.E., Koch, W.F., Stolz, J.W., et al.. Standard Reference Materials: Methods and Procedures Used

at the National Bureau of Standards to Certify Sulfur

in Coal SRMs for Sulftir Content, Calorific Value, Ash Content, NBS Spec. Publ. 260-94 (December

1984). PB85 165900**

Mulholland, G.W., Hartman, A.W., Hembree, G.G., et

al.. Standard Reference Materials: Development of a 1mm Diameter Particle Size Standard, SRM 1690, NBS Spec. Publ. 260-95 (May 1985). PB86 113693**

Carpenter, B.S., Gramlich, J.W., Greenberg, R.R., et

al.. Standard Reference Materials: Uranium-235

Isotopic Abundance Standard Reference Materials for Gamma Spectrometry Measurements, NBS Spec.

Publ. 260-96 (September 1986). PB87 108544**

Mavrodineanu, R., and Gills, T.E., Standard Reference

Materials: Summary of the Coal, Ore, Mineral, Rock, and Refactory Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-97

(September 1985). PB86 110830**

Hust, J.G., Standard Reference Materials: Glass Fiberboard SRM for Thermal Resistance, NBS Spec.

Publ. 260-98 (August 1985). SN003-003-02674-3*

Callanan, J.E., Sullivan, S.A., and Vecchia, D.F.,

Standard Reference Materials: Feasibility Study for the Development of Standards Using Differential Scanning Calorimetry, NBS Spec. Publ. 260-99

(August 1985). PB86 106747**

Taylor, J.K., Trahey, N.M., ed.. Standard Reference

Materials: Handbook for SRM Users, NBS Spec.

Publ. 260-100 (February 1993). PB93183796** Mangum, B.W., Standard Reference Materials: SRM

1970, Succinonitrile Tnple-Point Standard: A

Temperature Reference Standard Near 58.08° C, NBS Spec. Publ. 260-101 (March 1986). PB86197100**

Weidner, V.R., Mavrodineanu, R., Mielenz, K.D., et

al.. Standard Reference Materials: Holmium Oxide

Solution Wavelength Standard from 240 to 640 nm - SRM 2034, NBS Spec. Publ. 260-102 (July 1986). PB86245727**

Hust, J.G., Standard Reference Materials: Glass

Fiberblanket SRM for Thermal Resistance, NBS

Spec. Publ. 260-103 (September 1985). PB86 109949**

Mavrodineanu, R., and Alvarez, R., Standard Reference

Materials: Summary of the Biological and Botanical Standards Issued by the National Bureau of

Standards, NBS Spec. Publ. 260-104 (November

1985). PB86155561**

Mavrodineanu, R., and Rasberry, S.D., Standard Reference Materials: Summary of the Environmental

Research, Analysis, and Control Standards Issued by

the National Bureau of Standards, NBS Spec. Publ. 260-105 (March 1986). PB86204005**

Koch, W.F., ed.. Standard Reference Materials: Methods

and Procedures Used at the National Bureau of

Standards to Prepare, Analyze, and Certify SRM

2694, Simulated Rainwater, and Recommendations

for Use, NBS Spec. Publ. 260-106 (July 1986). PB86247483**

Hartman, A.W., and McKenzie, R.L., Standard Reference Materials: SRM 1965, Microsphere Slide (10 ^m Polystyrene Spheres), NBS Spec. Publ. 260-107 (November 1988). PB89153704**

Mavrodineanu, R., and Gills, T.E., Standard Reference

Materials: Summary of Gas Cylinder and Permeation Tube Standard Reference Materials Issued by the National Bureau of Standards, NBS Spec. Publ. 260-108 (May 1987). PB87209953**

Candela, G.A., Chandler-Horowitz, D., Novotny, D.B.,

et al.. Standard Reference Materials: Preparation and

Certification of an Ellipsometrically Derived

Thickness and Refractive Index Standard of a Silicon Dioxide Film (SRM 2530), NIST Spec. Publ. 260-109 (October 1988). PB89133573**

Kirby, R.K., and Kanare, H.M., Standard Reference

Materials: Portland Cement Chemical Composition

Standards (Blending, Packaging, and Testing), NBS

Spec. Publ. 260-110 (February 1988). PB88193347**

Gladney, E.S., O'Malley, B.T., Roelandts, I., et al.. Standard Reference Materials: Compilation of Elemental Concentration Data for NBS Clinical, Biological, Geological, and Environmental Standard Reference Materials, NBS Spec. Publ. 260-111 (November 1987). PB88156708**

viil
Marinenko, R.B., Blackburn, D.H., and Bodkin, J.B., Standard Reference Materials: Glasses for Microanalysis: SRMs 1871-1875, NIST Spec. Publ. 260- 11 2 (February 1 990) . PB902 1 5 807 * * Mangum, B.W., and Wise, J. A., Standard Reference

Materials: Description and Use of a Precision Thermometer for the Clinical Laboratory, SRM 934, NIST Spec. Publ. 260-113 (June 1990). PB90257643**

Vezzetti, C.F., Vamer, R.N., and Potzick, J.E., Standard Reference Materials: Bright-Chromium

Linewidth Standard, SRM 476, for Calibration of

Optical Microscope Lmewidth Measuring Systems, NIST Spec. Publ. 260-114 (January 1991). PB91167163**

Williamson, M.P., Willman, N.E., and Grubb, D.S., Standard Reference Materials: Calibration of NIST SRM 3201 for 0.5 in. (12.65 mm) Serial Serpentine Magnetic Tape Cartridge, NIST Spec. Publ. 260-1 15 (February 1991). PB91 187542**

Mavrodineanu, R., Burke, R.W., Baldwin, J.R., et al., Standard Reference Materials: Glass Filters as a Standard Reference Material for Spectrophotometry - Selection, Preparation, Certification and Use of SRM

930 and SRM 1930, NIST Spec. PubJ. 260-116 (March 1994). SN003-00303256-5*

Vezzetti, C.F., Vamer, R.N., and Potzick, J.E., Standard Reference Materials: Antireflecting-Chromium Linewidth Standard, SRM 475,

for Calibration of Optical Microscope Linewidth Measuring Systems, NIST Spec. Publ. 260-117

(January 1992). PB92-149798**

Williamson, M.P., Standard Reference Materials: Calibration of NIST Standard Reference Material 3202 for 18-Track, Parallel, and 36-Track, Parallel Serpentine, 12.65 mm (0.5 in), 1491 cpmm (37871

cpi). Magnetic Tape Cartridge, NIST Spec. Publ. 260-118 (July 1992). PB92-226281**

Vezetti, C.F., Vamer, R.N., and Potzick, Standard Reference Materials: Antiretlecting-Chromium Linewidth Standard, SRM 473, for Calibration of

Optical Microscope Linewidth Measuring System, NIST Spec. Publ. 260-119 (September 1992). Caskey, G.W., Philips, S.D., Borchardt., et al.. Standard Reference Materials: A Users' Guide to NIST SRM 2084: CMM Probe Performance

Standard, NIST Spec. Publ. 260-120(1994).

Rennex, B., Standard Reference Materials: Certification of a Standard Reference Material for the Determination of Interstitial Oxygen Concentration in Semiconductor Silicon by Infrared

Spectrophotometry, NIST Spec. Publ. 260-121

(1994).

*Send order with remittance to: Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20102. Remittance from foreign countries should include an additional one fourth of

the purchase price for postage. **May be ordered from: National Technical Information

Services (NTIS), Springfield, VA 22161. For information phone (703-487-4650) To Place an Order with PB# phone (800-553-6847)

ix

Contents

1. Introduction 1

2. Design Features . 3

3. Calibration 4

4. Care and Cleaning o , . 4

5. Assembly and Setup 5

6. CMM Testing Considerations ... 6

7. Performance Tests 8 Acknowledgements 11 References 11 Appendix A. SRM 2084 Uncertainty Analysis 12 Table Al:

Master Sphere Uncertainty 14 Table A2

Diameter Calibration Measurement Uncertainty .... 16 Table A3:

Out-of -Roundness Calibration Measurement Uncertainty. 17 Appendix B: SRM 2084/2085 Relevant Material Properties 18

xi

A Users' Guide to NIST SRM 2084:

CMM Probe Performance Standard

G.W. Caskey, S.D. Phillips, B.R. Borchardt, D.E. Ward, D.S. Sawyer

Precision Engineering Division National Institute of Standards and Technology

Introduction

Over the past two decades, the coordinate measuring machine (CMM) has matured as a technology for both shop floor and gage lab three-dimensional coordinate metrology. During this time, national and international committees were organized to address the performance

specification and assessment of these machines, their subsystems and accessories. The results were a number of published standards which provide a set of specifications and testing methodologies for the assessment of CMM performance. These tests require the use of various

precision artifacts which, in many cases, have been developed to fulfill the demand created by

the issuance of these standards. The CMM Probe Performance Standard, Standard Reference Material (SRM) 2084, developed

at the National Institute of Standards and Technology (NIST), is one such precision artifact. It was developed to facilitate point-to-point probing performance evaluation of a coordinate measuring machine (CMM) according to the American National Standard ASME B89.1.12M1990 "Methods for Performance Evaluation of Coordinate Measuring Machines"[l]. Additionally,

this SRM carries a NIST sphere calibration for both roundness and diameter (the diameter

calibration is not required by the ASME Standard) which makes it applicable to addressing

additional probe performance issues. SRM 2084 consists of (see figure 1) a precision sphere mounted on a stem and a support stand with holes for mounting the sphere stem in either a

horizontal, vertical, or 45 degree orientation. The spheres are available in two sizes, the standard 10 mm diameter tungsten carbide sphere which is included as part of SRM 2084 and an optional 25 mm diameter stainless steel sphere designated SRM 2085. Additional 10 mm tungsten carbide spheres can be purchased separately as SRM 2084R. These spheres are interchangeable, with each one mounted on a 3.2 mm (0.125 in) diameter stem. Included with SRM 2084 are:

• 10 mm tungsten carbide sphere on a tungsten carbide stem with a protective vinyl cap and

plastic storage vial

• Stainless steel stand

• Wooden storage case

• Mounting hardware for 5/16 in, 3/8 in, 1/2 in, M8, MIO, and Ml 2 machine inserts

• Ten (10) brass-tipped #6-32 x 1/4 in set screws in a plastic storage vial

• 1/16 in hex key

• Spare storage vial for optional additional sphere/stem

• Copy of the Standard Reference Material Certificate and roundness traces covering this SRM

• Copy of the ASME B89. 1 . 1 2M- 1 990 Standard
Horizontal, vertical and

45° mounting orientations

V^__^ \ — Tungsten carbide

Q) \ sphere and shaft j

Figure 1. Highlights of SRM 2084. Note: unit shown with two optional 10 mm spheres

1/16 Hex Key

Figure 2. SRM 2084 and accessories in storage case

2
SRM 2085 consists of:

• 25 mm stainless steel sphere on a tungsten carbide stem with a protective vinyl cap and

plastic storage vial

• Copy of the Standard Reference Material Certificate covering this SRM

Design Features

The sphere is constructed from tungsten carbide to provide abrasion and corrosion resistance to withstand repeated probing and handling. The stem is also constructed from tungsten carbide to provide high stiffness, necessary to minimize bending due to probing forces. For the stand,

stainless steel was chosen for moderate stiffness and corrosion resistance characteristics. The

stand height is sufficient to allow probing access while still maintaining adequate stiffness. The

bottom of the stand is relieved to provide an annulus which is lapped flat for a more secure mounting surface. Two holes in the stand base accommodate the various sized mounting screws provided with SRM 2084. The stand has three sphere/stem mounting holes; horizontal, vertical, and inclined at 45 degrees,

to provide greater accessibility for the array of probe configurations available on CMMs today. A sphere/stem is secured in the stand with two brass tipped set screws, which are approximately

1 20 degrees apart and perpendicular to the stem. The softer brass on tungsten carbide material combination ensures that the set screws will not mar or raise a burr on the stem. Two sphere sizes were chosen to accommodate different CMM probe testing requirements. The

10 mm diameter sphere is small enough to allow probing points below the equator for most sizes of styli. (For these SRMs no probing points should be taken below 50 degrees from the equator due to uncertainty about the sphere form in the region near the stem (see figure 3).) Alternatively, a 25 mm diameter sphere is better suited for contact scanning tests due to the

larger radius of curvature.

Avoid this region

Figure 3. SRM sphere "no measurement zone"

3
Calibration

The spheres included as part of SRM 2084 and 2085 are cahbrated for both form (roundness) and

size (diameter). Cahbration values are given on the accompanying SRM certificate and can be

identified by the serial number engraved on the stem. The uncertainty budgets for these

calibrations are given in Appendix A. These spheres were measured over a period of one year

with no detectable change in either size or form, establishing the short term stability of the

calibration values. The sphere size is assessed through a two-point (parallel plane) comparison with NIST master

spheres of the same nominal diameter. The sphere is compared to tungsten carbide masters using

a redundant measurement technique designed to minimize extraneous influences such as operator

bias and thermal drift. These comparisons are conducted on a high precision bench micrometer. The sphere roundness deviations are assessed through a series of five roundness traces made on

a roundness measuring instrument. The traces consist of a single equatorial trace and four great

circle traces inclined at 45 degrees to the equator. The inclined traces are made in orthogonal

pairs with a 90 degree phase difference between the two pairs. (For the above discussion, the equator is defined as the great circle whose normal is parallel to the axis of the stem.) The out-of-roundness of this SRM was treated differently than a standard out-of-roundness

calibration. For the sphere, an upper threshold on any of the out-of-roundness measurements (a

total of 5 per sphere) was established as 0.076 |im. Any sphere with a roundness trace greater than this threshold value was rejected. Therefore, the upper limit combined with the out-of- roundness measurement uncertainty provides a worst case out-of-roundness for any of the 5

traces.

Care and Cleaning

Although the spheres that are part of these SRMs are constructed of a robust material, it should be kept in mind that they are calibrated artifacts and must be treated with reasonable care. A

yellow vinyl cap is supplied with each sphere so that it may be covered and protected when not

in use. Additionally, during extended periods of nonuse, it is recommended that the sphere be removed from the stand and placed in its storage vial. In the event of damage (or suspected

damage) to the sphere, the SRM should be removed from service until the sphere can be

recalibrated or replaced. The sphere may be cleaned by wiping with a clean, soft lint-free cloth or lens paper. A more

thorough cleaning can be accomplished by dampening the cloth with a mild uncontaminated

solvent, such as methyl alcohol (methanol). Care should be exercised in selecting both the cloth and the solvent as they can leave behind dust and chemical residues which can affect any

subsequent measurements. Under no circumstances should an abrasive material or solution be

used to clean a sphere as this could invalidate the calibration. 4
Assembly and Setup

Select a suitable location on the CMM worktable for the placement of the CMM Probe Performance Standard. The concern here is to allow for adequate probing access of the entire sphere, keeping in mind that for some testing configurations offsets of 50 mm or more

perpendicular to the probe axis may be required. It may also be desirable to leave the stand permanently fixtured to the worktable, so select an area that will not interfere with routine measurements. Fasten the stand to the CMM using one of the threaded inserts in the machine

worktable and the corresponding socket head cap screws supplied with SRM 2084. Next, remove

the sphere/stem from the protective vial and insert the stem in the stand hole with the desired

orientation. The stem is secured in the stand by tightening the two #6-32 set screws corresponding to that hole. Using the supplied hex key, firmly tighten the set screws (by hand

only) to ensure stable mounting. At this point it is a good idea to clean the sphere to remove

any dirt or other contaminants that might have collected on the sphere during handling. For high

accuracy measurements, a thermal "soak" time of approximately one-half hour (after assembly

and cleaning) should be observed to allow the artifact to reach thermal equilibrium with its environment.

In assembling the unit it should be noted that the distance between the bottom of the sphere and

the top of the stand is an important consideration. An excessive sphere-to-stand offset can

degrade the measurements (depending on the precision desired) through bending of the stem. This is primarily a concern with analog or proportional probes where sustained probe-to-part contact is integral to the measurement process and not so much with a switching probe where

the contact is for shorter periods of time (usually less than a second). Stem bending can appear

as an apparent sphere form error (sphere out-of-roundness) and/or probe lobing error. To

minimize the effects caused by stem bending, it is recommended that the stem be inserted such

that there is 5 mm (0.20 in), or less, between the bottom of the sphere and the top of stand as shown in the figure 4.

Figure 4. Schematic showing recommended sphere-to-stand offset distance (similarly for the remaining two mounting orientations)

^ 5.0 mm

5
At this distance, stem deflection will be on the order of 0.05 ^m (2.0 |jin) for 0.1 newton (10 grams) of probing force. For other sphere offset/probing force combinations, the amount of stem

bending, 6, can be calculated from the equation:

5 = F[1.09xl0"^ X (L + 8.81)' + 0.17]|im

where, F = Probing force, newtons L = Distance from bottom of sphere

to top of stand, in millimeters

The above equation is an approximation for the average bending, developed from beam theory and empirical data, and is accurate to better than 0.01 |Lim for SRM 2084 (10 mm sphere) with probing forces up to 0.5 N (50 g). As can be seen from the equation, the stem bending is a function of the sphere offset and probing force. The first term (l.OQxlO""* ) is a combination of

the factors that are a function of the material properties and stem diameter. The second term

(L + 8.81)^ is the "effective" cantilevered length which includes the distance from the set screws

to the top of the stand, the distance from top of the stand to the bottom of the sphere, and the radius of the sphere. The final term (0.17) is the deflection, per newton, of the stainless steel stand determined from experimental observations. CMM Testing Considerations

A properly selected measurement/data analysis strategy for SRM 2084 can reveal a significant amount of useful information about the CMM and probe subsystem (i.e., probe, indexable probe

head, probe changer, multiple stylus configurations). Table 1 shows the range of machine and

probe errors that can be detected when measuring a calibrated sphere.

Table 1. - CMM Errors Revealed Through Calibrated Sphere Measurements [2]

Radial Deviations

• CMM Repeatability

• Probe Repeatability

• Probe Lobing

• Stylus Ball Form, i.e., out-of-roundness

• Stylus Bending

• CMM Dynamics (Vibrations)

• Probe Head Repeatability

• Probe Offset Vector Errors (multiple styli/probes)

• Probe Changer Repeatability

• Short-Range Scale Errors

Ball Diameter

Deviations

• Effective Stylus Diameter (probe calibration)

6
These errors, although not all independently quantifiable, can be realized through machine testing

in accordance with a national or international standard governing the performance verification and accuracy specification of CMMs or any other well designed performance test. For the latter, several principles are important to note. When testing the machine probing system, using the same artifact for both probe calibration (sometimes referred to as probe qualification) and performance testing should be avoided (in some Standards it is expressly forbidden). For performance testing which uses the sphere size

in the analysis, it is essential that a calibrated sphere other than the one used for probe calibration be employed. If sphere form is the quantity being used in the performance assessment, a second

sphere is also recommended. However, for this case a single sphere can be used for calibration and performance testing, if as a minimum, the sphere is reoriented. This will help to reveal the

errors that can be masked when using the same sphere for both tasks. Additionally, the dimensional accuracy of the test sphere (form and in some cases size) should be some fraction of the magnitude of the error that is under assessment. For example, a l-to-5 ratio is recommended in the ANSI/ASME B89.1.12M-1990 Standard.

In order to accurately assess the probe performance, the tests should be carried out as close as possible to normal part measuring conditions, i.e., in the same environment, with representative

probe configurations (same probe, stylus length, stylus orientation, number of styli, etc.), and

similar machine motion parameters (probing velocity, probe approach distance, etc.). These

variables can have a significant irhpact on machine performance and testing with different parameter combinations can reveal the extent of these effects. It is therefore advisable, where

practical, to test all probe combinations that are of interest. For all tests, the probe configurations

relevant to that test should be calibrated using the manufacturer's specified procedures.

The sampling strategy (number of probing points and distribution of these points) is another important consideration when making the sphere measurement(s). The strategy chosen will depend on whether sphere size, form, or center location is being assessed. Generally, more

points with a greater distribution are required when measuring form. For example, the probe

performance tests found in published Standards require 25 to 49 points where form is to be

evaluated. In the absence of other guidance, eight or more points uniformly distributed over at least a hemisphere can be a quick, although less thorough, probe performance test.

Finally, it is worth restating that both the test sphere and the probe stylus should be clean and

free from dust (see section on Care and Cleaning). Many films (skin oils, chemical residues) and common dust particles can be many micrometers thick. A "bump" of this magnitude can be

detected by many CMMs and can, therefore, adversely affect test results.

7
Performance Tests The first two tests, probing performance and repeatability, were taken from the American

National Standard B89.1.12M-1990 and are therefore only outlined in this document (the user

is referred to the Standard for more detailed information). The remaining two tests, multi-tip probing and scanning performance, do not appear in the Standard and will be treated in more

detail. In general, the tests presented here were developed for the purpose of verifying a machine's conformance to a published standard. If the intent is to establish the limits of a CMM's performance, it is suggested that the test be repeated several times to provide a more

accurate picture of a machine's range of variability for that test.

Point-to-Point Probing Performance The probe performance test, B89.1.12M Section 6.1, is designed to evaluate the probing error

(pretravel variation) for several different probe configurations. For this test, 49 points consisting of one point on the pole and 12 points on 4 levels with polar angles of 30, 60, 90, and 100

degrees, are measured. Between levels the 12 point pattern is rotated 10 degrees to provide more

coverage of the sphere and variability in the probe approach vectors. This test is then repeated with a minimum of three different stylus configurations. The probing performance is defined as the range of the radii to each measurement point calculated from the least squares sphere center

for each stylus configuration. If the CMM software has the capability to assess sphericity (based on a least squares center), the value obtained from this data analysis is equal to the range of the

radial residuals and therefore may be used interchangeably. Although this test does not require

a calibrated sphere diameter, this information can be used in conjunction with this test to verify the probe calibration (effective probe diameter) by comparing the calibrated value with the measured value. This later test is analogous to the B89.1.12M Bi-directional Length Measurement Capability (section 5.6) which uses a gage block for similar purposes.

Repeatability The second test addresses the repeatability of the CMM (B89.1.12M-1990 section 5.3), machine

and probe subsystem. For this test, a sphere is rapidly measured (to preclude thermal drift) ten times using four probing points. The range of the ten sphere center coordinates provides a measure of the machine repeatability on an axis-by-axis basis.

Probe/Stylus Changer Repeatability

If the CMM is equipped with an automatic probe or stylus changer, a variation of the above

repeatability test that integrates either of these devices can be performed. This would be done

by putting a single probe/stylus into the changer and immediately retrieving it between each of

the ten measurements. The range of the sphere center coordinates from this test could be compared with a results obtained from the repeatability test above to establish the repeatability of the probe/stylus changer.

8
Multi-Tip Probing Performance

Multi-tip probing encompasses the use of multiple styli ("star" or cluster probes) on a single probe, an indexable probe in more than one orientation, or a combination of the two during the course of a measurement. The purpose of this test is to assess the error induced when multiple

probe configurations are used in a single feature measurement. These errors arise from three

sources: the accuracy of the effective stylus diameter (probe calibration), the ability of the probe head to repeatedly index to a given position(s) (probe head "lock-up" repeatability) and the accuracy of the probe tip's position with respect to the CMM coordinate system (probe offset vector accuracy). Although the multi-tip probing performance test is similar in procedure to the point-to-point probing performance test, the two are distinct and necessary because they address

different errors. An interesting test situation exists for the indexable probe heads. Because these devices typically have more than five hundred different indexable positions, incorporating all of these positions

in a single performance test would be highly impractical. However, due to the probe head's construction only a limited number of unique "lock-up" positions exist. It is therefore possible

to assess all of these discrete positions in a single test, thus providing a full evaluation of the probe head performance. Table 2 shows an example of one probe head's discrete positions with

a largest axis angular travel of 360 degrees in 7.5 degree increments.

Table 2. - Example Probe Head Indexing Positions

Position

Vert. Axis

(deg.) Horiz.Axis

(deg.) Position Vert Axis

(deg.) Horiz Axis(deg.)

1 0.0 0.0 9 60.0 -60.0 2 7.5 127.5 10 67.5 67.5

3 15.0 -105.0 11 75.0 -165.0 4 22.5 22.5 12 82.5 -37.5

5 30.0 150.0 13 90.0 90.0 6 37.5 -82.5 14 97.5 -142.5

7 45.0 45.0 15 105.0 -15.0

8 52.5 172.5 16 0.0 112.5

In preparation for this test, a number of representative probe configurations are identified and

calibrated (qualified). The sphere is then measured using each of the different probe

configurations to sample a minimum of one point. A total of 49 points are required at locations equivalent to those used for the point-to-point probing test. These points are then used to construct a sphere using the CMM sphere fit algorithm. The multi-tip probing performance is the form of the substitute sphere as calculated by the CMM sphericity algorithm.

9
Contact Scanning Performance The scanning test is aimed at assessing the performance of CMMs with the capability of measuring parts in a contact stylus scanning mode. This test applies regardless of whether the scan data is to be used to evaluate the form or size of the surface/feature. For this test, the scanning parameters such as speed and data density should be consistent with normal (or intended) measuring practices for that machine. The user should be aware that exceeding

manufacturer's suggested measurement parameters may cause erratic results. Additionally, any

probe configuration may be used for this test with the above provisos.

This contact scanning test utilizes a 25 mm stainless steel ball (SRM 2085) and makes use of both the form and size calibrations. For this test the sphere is inclined at 45 degrees to the probe

(ram) axis to include all of the machine's axes. The procedure is to scan four progressively more

difficult paths along the sphere. These paths consist of a scan along the equator, a scan in a plane parallel to and offset 8 mm from the equator, a hemisphere scan beginning and ending at the equator and passing through the pole, and a similar path perpendicular to the previous scan

but offset 8 mm from the pole (see figure 5). The data can be analyzed as in the point-to-point

probing test above, with the data from all four scan lines used to calculate a substitute diameter and sphericity using the CMM's standard algorithm. The degree of agreement between the calculated and calibrated diameter values provides an assessment of the CMM's ability to accurately resolve features of size when used in scanning mode. Similarly, the calculated

sphericity is a measure of the machine's capability to assess features of form. (Although the SRMs are not explicitly calibrated for sphericity, the maximum allowable out-of-roundness

deviations, coupled with the extensive coverage of the sphere using five roundness traces, assures

to a high degree of certainty, that the deviations can be attributed to the performance of the probe and CMM.)

Figure 5. Contact scanning test scan lines

10
Although this test provides a useful picture of a CMM's scanning performance, it is important

to point out several limitations. Like most of the other performance tests, the results depend on

the conditions (including measurement parameters, and type and quality of the artifact) that were

prevalent during the test. For example, the surface finish spatial wavelength can excite a resonance in some machines and/or probes. This test also does not demonstrate the behavior of

the measurement system when drastic part transitions, such as comers and edges are encountered.

Additionally, the sphere probe dynamics are strongly affected by both the finish and the lubricity of the surface.

Acknowledgements

The development work for this SRM was partially funded by the NIST Standard Reference

Material Program, the U.S. Air Force Combined Calibrations Group, and the U.S. Navy

Manufacturing Technology Program. The authors would like to thank Mr. K. Eberhardt and Mr. Ralph Veale of NIST for their assistance and comments.

References

1. ANSI/ASME B89.1.12M, "Methods for the Performance Evaluation of Coordinate Measuring

Machines," American Society of Mechanical Engineers, New York, NY, 1990.

2. Phillips, S.D., B. Borchardt, G. Caskey, "Measurement Uncertainty Considerations for Coordinate Measuring Machines," NISTIR 5170, National Institute of Standards and

Technology, Gaithersburg, MD, April 1993.

3. Taylor, B.N., C.E. Kuyatt, "Guidelines for Evaluating and Expressing the Uncertainty of NIST

Measurement Results," NIST Technical Note 1297, National Institute of Standards and

Technology, Gaithersburg, MD, January 1993.

4. Reeve, Charles P., "The Calibration of a Roundness Standard," NBSIR 79-1758, National Bureau of Standards, Gaithersburg, MD, June 1979.

5. Puttock, M.J., E.G. Thwaite, "Elastic Compression of Spheres and Cylinders at Point and Line

Contact," National Standards Laboratory Technical Paper No. 25, Commonwealth Scientific and Industrial Research Organization (CSIRO), Melbourne, Australia, 1969.

6. Young, Warren C, Roark's Formulas for Stress and Strain, 6th Ed., McGraw-Hill Book

Company, 1989.

11
Appendix A: SRM 2084 Uncertainty Analysis

The uncertainty of the sphere calibration values was calculated in accordance with the current NIST [3] policy which establishes the measurement uncertainty as the root-sum-square of the contributing sources multiplied by a coverage factor k=2. This analysis recognizes two

components of uncertainty, those evaluated through statistical means (Type A), and those evaluated by other means (Type B). For this assessment. Type B uncertainties were assumed to be from a rectangular (uniform) distribution. The sources of the uncertainties and the associated

calculations (standard uncertainties, la) are detailed below and summarized in tables A2 and A3.

Out-of-roundness Calibration

The uncertainty budget for the out-of-roundness of these SRMs is composed of three terms: measurement instrument spindle error, operator interpolation error, and measurement repeatability. The roundness measuring instrument spindle error was assessed using a quasi closure technique

[4] which allows the isolation and quantification of the spindle out-of-roundness. Under this technique, a series of roundness traces were made on a single cylinder (with low order and

amplitude form error), indexing the artifact through an angle of 30 degrees between traces. The

traces are made on nominally the same circular cross section with different starting positions on

the circle. For this angular rotation, a total of 12 traces were used (360-=-30) to deconvolve the spindle error. This procedure was repeated 9 times and the range of the values was used as the ± limits of a uniform distribution for the purposes of assigning the uncertainty due to spindle

error.

Standard Uncertainty = 0.041nm/v/3" = 0.024 [im

Operator interpolation uncertainty results from the calibration technician's finite ability to accurately subdivide the scale divisions on the roundness charts. For the roundness charts associated with these SRMs, values uniformly distributed between ± 1/10 of a scale division were

established as a conservative estimate of the operator's interpolation uncertainty. The actual uncertainty also depends on the chart magnification which, in this case, was 0.127 |im/div. Therefore the standard uncertainty due to operator interpolation is:

Standard Uncertainty = (0.127 ^m/div)/(10x/3") = 0.007 fim

The final out-of-roundness uncertainty contribution is the repeatability of the measurement. This was assessed from the same data as the spindle out-of-roundness uncertainty, by calculating the pooled variance of the spindle out-of-roundness measurements, i.e., combining the variances of

12
the 9 estimates of the spindle error assessed at 12 points. The standard deviation obtained from

the pooled variance provided an estimate of the measurement repeatability. In this case the value was calculated as

Standard Uncertainty = (4.37xl0>m') = 0.006 |im

12

\| n

Diameter Calibration

The diameter calibration uncertainty is composed of master sphere uncertainty, differential thermal expansion, differential deformation, measurement repeatability, sensor linearity, as well

as contributions from the measurement sphere out-of-roundness and uncertainty in measurement

sphere out-of-roundness. The uncertainty in the size of the master sphere constitutes a separate and unique error budget. There are many factors which contribute to master sphere uncertainty which can be grouped into five categories; those quantities which are associated with four color

interferometry, thermal expansion of the master sphere, contact deformation, geometry (both master sphere and flat/platen), and measurement repeatability. All of these terms were estimated from known measurement system/process variables (see table Al below), with the exception of master sphere out-of-roundness. The uncertainty due to master sphere out-of-roundness was

assessed from 200 random diameter measurements of the master sphere. Because the measurements were made in 40 groups of 5 measurements each, the variances of the 40 groups were calculated and pooled to determine the standard deviation of the process. This value also included the repeatability of the measurement which was subsequently quantified in a similar manner and removed (see comparator repeatability below).

n n Standard Uncertainty = ^ s^^ v/(1.31xlO^-3.71xlO^)|im2 = 0.031 |im

%| n n

where variance of the master sphere diameter

variance of the check standard diameter

13
Table Al. - Master Sphere Uncertainty Source Standard Uncertainty (la) (Mm)

Interferometry Phase shift correction 0.002

Uncertainty in cadmium light wavelength < 0.001

Pressure correction < 0.001 Temperature correction < 0.001 Humidity correction 0.002

Slit and obliquity correction 0.001 ThermalUNE 0.012 Temperature correction < 0.001 Deformation Correction Force correction 0.002 Force variations due to location 0.002

Material property variations 0.010 Geometry

Flat/platen geometry 0.007 Master sphere out-of-roundness 0.031

Repeatability Measurement repeatability 0.005

Fringe fraction estimation 0.009 Combined Standard Uncertainty 0.035

A temperature difference between the two spheres (master and measurement) during the comparison process can cause a relative expansion of one sphere with respect to the other. It is hard to correct for this differential expansion because it is impractical to directly monitor the

14
temperatures of the individual spheres. Therefore, an estimate of this effect on the uncertainty of the diameter calibration must be made. There is also a component of differential expansion

that results from a lack of accurate knowledge of the sphere's coefficient of thermal expansion. For most materials an uncertainty of ± 10% from nominal is the accepted value which results in a worse case when the master and measurement spheres are at the extremes (one sphere at +

10%, the other at - 10 %). For the facilities and procedures used in this calibration, a temperature difference of ± 0.1 °C between the spheres is a conservative estimate for both

calculations.

Standard Uncertainty = (0.1 °C x 5.0 ppm/°C x 0.01 mmV/T = 0.003 |im

Standard Uncertainty = (0.1 °C x 1.0 ppm/°C x 0.01 mm)/v/3" = 0.001 pm

Combining the two values in quadrature and assuming a uniform distribution, the estimated

uncertainty is:

Combined Standard Uncertainty = y/(0.003[im)^ +(0.001 iimY = 0.003 pm

Similarly, if the material properties differ from their nominal values for the master and/or measurement spheres (modulus of elasticity, Poisson's ratio) then an uncertainty in the contact deformation correction is introduced. Because for this comparison the master and measurement

spheres are of the same material, there is no nominal deformation correction required and the uncertainty arises from an uncompensated differential deformation. Because the range of material

properties is often reported as ± 10% from nominal, therefore, the value was calculated as the difference of the extreme values (one sphere at + 10%, the other at - 10 %). (Due to their complexity, the contact deformation equations will not be presented here and the user is referred

to sources which treat this topic in greater detail 15,6].) This range was assumed to be the half width of a rectangular distribution and was calculated as:

A5^^^+ A5^j„ (0.013 + 0.016)pm

Standard Uncertainty = = = 0.008 pm

2-J3 2-yf3

The repeatability of the comparator is another contributor to the uncertainty of the diameter

calibration. To assess the magnitude of this term, the pooled variance of the 5 measurements

each of 40 different spheres was calculated. It is important to point out that for the 5 measurements of a single sphere, the same diameter was gaged each time which removed any

apparent non-repeatability due to sphere form. The resulting standard deviation was used as an

estimate of the comparison process repeatability.

15
Standard Uncertainty (0.01 l|nm^) = 0.017 iim 40

The final terms in the uncertainty analysis are the out-of-roundness of the measurement sphere and the uncertainty in the out-of-roundness value. The out-of-roundness uncertainty propagates

directly into the diameter uncertainty. The measurement sphere out-of-roundness value is assumed to be the half width of a uniform distribution centered about the calibrated diameter. The contribution is:

Standard Uncertainty = (0.076)/ /s" = 0.044 ^m

Table A2. - Diameter Calibration Measurement Uncertainty Source Type Standard

Uncertainty (lo) (Mm)

Master Sphere Uncertainty B 0.035

Transfer Uncertainty

Differential thermal expansion B 0.003

Differential deformation B 0.009

Repeatability of comparison A 0.017 Transducer linearity B < 0.001

Geometry Conversion

Sphere out-of-roundness B 0.044

Uncertainty in out-of-roundness A 0.026 Combined Standard Uncertainty 0.065 Expanded Uncertainty - Coverage Factor k=2 0.130

16
Table A3. - Out-of-Roundness Calibration Measurement Uncertainty Source Type Standard

Uncertainty (la)

(jim) Spindle Out-of-roundness B 0.024

Operator Interpolation B 0.007 Measurement Repeatability A 0.006 Combined Standard Uncertainty 0.026 Expanded Uncertainty - Coverage Factor k=2 0.051

17
Appendix B: SRM 2084/2085 Relevant Material Properties

The user should be aware that these are average material property values obtained from various sources.

It is known that these properties can vary as much as ± 10 % from the accepted values.

Tungsten Carbide (10 mm spheres, all stems):

Modulus of Elasticity 650 GPa

Poisson's Ratio 0.22

Coefficient of Thermal Expansion 5.0 ppm/°C

440C Stainless Steel (25 mm spheres):

Modulus of Elasticity 200 GPa

Poisson's Ratio 0.30

Coefficient of Thermal Expansion 10.2 ppm/°C

303 Stainless Steel (stands):

Modulus of Elasticity 193 GPa

Poisson's Ratio 0.30

Coefficient of Thermal Expansion 17.0 ppm/°C

18
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