1、ASME B1 TECHNICAL REPORT Measurement Uncertainty for 60 deg. Screw Thread Gage Element Measurement (Inch and Metric) The American Society of Mechanical Engineers 345 East 47th Street, New York, N.Y. 1001 7 - Date of Issuance: April 30, 1993 ASME is the registered trademark of The American Society of
2、 Mechanical Engineers. No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise. without the prior written permission of the publisher. Copyright 0 1993 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A. FOREWORD (This
3、Foreword is not part of the B1 Technical Report.) Every measurement has a degree of uncertainty. This problem surfaces when screw threads had to assemble and be interchangable. Early standards writers provided safeguards by estab- lishing a common basic size where the products limits were not permit
4、ted to cross. All forms variations which result in a functional size had to meet this requirement. As time progressed screw thread writers simplified the concept by placing Class 3 maxi- mum-material pitch diameter of both product and gage for internal and external threads at basic, assuming both ga
5、ge and product have no form variations. By doing this, it became difficult to manufacture gages with close tolerances to gage marginal product with certainty. This Report does not solve the screw thread standards concept. It recognizes that gages shall be made to specified tolerances by the gagemake
6、r, but may be outside the tolerance by a second partys uncertainty. At the October 1987 meeting of the ASME B1 Committee in New York City, a working group was created to address uncertainty. After several meetings, a scope and tentative meas- urement unceifainty values were proposed at the April 198
7、9 meeting in Orlando, Florida. This Report represents the best estimates for measurement uncertainty for gage sizes through 12 inches (300 millimeters). A gage is acceptable when a second partys measurement exceeds the tolerance by the tabulated value. The uncertainty value may be changed at a futur
8、e date if statistical data justify such a change. Suggestions for the improvement of this Report will be welcome. They should be sent to This Technical Report was approved by the ASME Board on Standardization on October 19, Secretary, ASME B1 Main Committee, 345 East 47th Street, New York, NY 10017.
9、 1992. 111 . ASME STANDARDS COMMllTEE 91 Standardization and Unification of Screw Threads (The following is the roster of the Committee at the time of approval of this Technical Report.) COMMllTEE PERSONNEL J. R. Anderson R. J. Browning R. M. Byrne D. P. Cadieux F. G. Calderone F. H. Cantrell R. S.
10、Chamerda R. Dodge P. H. Drake A. E. Ellis H. W. Ellison C. G. Erickson W. C. Farrell, Jr. R. E. Ferry, Jr. G. A. Flannery D. S. George J. Greenslade J. 0. Heinze R. R. Hyman C. W. Jatho S. P. Johnson S. I. Kanter J. Krippes OFFICERS E. Schwartz, Chairman K. E. McCullough, Vice Chairman C. J. Gomez,
11、Secretary R. W. Lamport R. S. LaNier J. B. Levy K. E. McCullough J. C. McMurray D. Miskinis W. R. Newman A. Painter G. A. Russ R. J. Sabatos D. M. Satava M. M. Schuster R. H. Searr R. E. Seppey A. D. Shepherd, Jr. V. B. Shook A. G. Strang J. F. Sullivan R. L. Tennis A. F. Thibodeau A. M. Wilkerson C
12、. J. Wilson V CONTENTS . Foreword 111 Standards Committee Roster v 1 Introduction . 1 2 Scope 1 3 Definitions . 1 4 Estimates of Measurement Uncertainty . 2 5 Application 3 6 Bibliography 3 Figure 1 Gage Acceptance Using Measurement Uncertainty (New and Used Gages) . 3 Tables 1 Estimated Uncertainty
13、 Values for Screw Thread Gages (Inch) . 2 2 Estimated Uncertainty Values for Screw Thread Gages (Millimeters) . 2 vii ASME B1 TECHNICAL REPORT MEASUREMENT UNCERTAINTY FOR 60 DEG. SCREW THREAD GAGE ELEMENT MEASUREMENT (INCH AND METRIC) 1 INTRODUCTION Measurement uncertainty is inherent in all types o
14、f measurement. A better understanding and definition of this factor is necessary to promote its acceptance within the screw thread industry. Uncertainty in measurement is documented in many dimensional measurement areas. (See references at the end of this Report.) However, no current standards are a
15、vailable to direct the screw thread industry. This Report is intended to provide: (a) an explanation of measurement uncertainty; (b) a tabulation of uncertainty estimates for the cali- (c) a guide in the resolution of disputes arising from bration of screw thread gage elements; and difference in scr
16、ew thread measurement. 2 SCOPE This Report provides estimates of uncertainty associ- ated with the measurement of pitch diameter, lead and flank angle only for screw thread gages. It is intended that these estimates will be used as a guide to resolve meas- urement disputes arising between any two pa
17、rties cali- brating the same gage. 3 DEFINITIONS The following definitions are based upon ANSVASQC M1-1987, Calibration Systems. 3.1 Uncertainty (Measurement) An estimate of the range of values about the measured value in which the accepted value is believed to lie. A total uncertainty represents th
18、e combination of a measure of the random error (e.g., some multiple of the standard deviation) and the estimated bounds to the systematic error. The term is inversely related to the term accuracy in that an instrument or measurement with the greater uncertainty is said to have the lesser accuracy an
19、d vice versa. If one figure is given as the total uncertainty, this figure is the sum of the limits due to random and system- atic errors unless other means of combining such limits are specified. 3.2 Random Error The limits of variation in measured value of unpre- dictable sign and magnitude occurr
20、ing when measure- ments of the same quantity are made under effectively identical conditions. 3.3 Systematic Error A contribution to the total uncertainty comprised of the combined effects of all nonrandom sources of uncer- tainty, known or unknown, which cannot be replicated during the calibration
21、or measurement of a characteristic which tends to offset uniformly or predictably all results of repeated applications of the same measurement process at the time of the measurement. Such an error may be reduced or eliminated by adjustments or application of a correction factor. 3.4 Measured Value T
22、he stated or recorded value after all adjustments and corrections, if any, have been incorporated into the ob- served value. 3.5 Accuracy The extent to which the measured value of a quantity agrees with the accepted value for that quantity. 3.6 Precision The degree of agreement among independent mea
23、s- urements of a quantity,under specified conditions. 1 MEASUREMENT UNCERTAINTY FOR 60 DEG. SCREW THREAD GAGE ELEMENT MEASUREMENT (INCH AND METRIC) TABLE 1 ESTIMATED UNCERTAINTY VALUES FOR SCREW THREAD GAGES (All Dimensions in Inches Except Where Noted) 0.060 Through Above 0.190 Above 1.500 Above 6.
24、000 0.190 Through 1.500 Through 6.000 Through 12.000 Nominal Thread Size Ext. Int. Ext. Int. Ext. Int. Ext. Int. Pitch diameter f0.00008 Note (I) fO.0001 f0.0002 k0.00015 f0.0003 f0.0002 f0.0003 Lead 50.00008 Note (I) 50.0001 f0.0002 +0.00015 f0.0002 f0.0002 f0.0002 Flank angle Note (211 1 through 1
25、2 TPI . . 503 +05 -103 f05 f03 f05 13 through ,32 TPI k05 . f05 f07 505 f07 f05 f07 33 through80 TPI f010 . f010 f015 fO“10 k01 5 . . TABLE 2 ESTIMATED UNCERTAINTY VALUES FOR SCREW THREAD GAGES (All Dimensions in Millimeters Except Where Noted) 1.5 Through Above 5.00 Above 38.00 Above 150.00 5.00 Th
26、rough 38.00 Through 150.00 Through 300.00 Nominal Thread Size, mm Ext. Int. Ext. Int. E*. Int. Ext. Int. Pitch diameter f0.0020 Note (1 )I k0.0025 f0.0051 f0.0038 f0.0076 k0.0051 k0.0076 Lead k0.0020 Note (I) f0.0025 f0.0051 k0.0038 f0.0051 f0.0051 f0.0051 Flank angle Note (2)l P = 2.2 through 25 .
27、. f03 - +V5 f03 f05 f03 f05 P = 0.8 through 2 . f05 . f05 f07 fO“5 +V7 f05 f07 P = 0.3 through 0.75 f010 . f010 f015 +VI 0 f015 . . GENERAL NOTES TO TABLES 1 AND 2: (a) External pitch diameter measurements made over thread wires require consideration of the influencing factors of measuring wires and
28、 the gage blocks.-Uncertainty values for pitch diameter include variation of the best wire size. These wires are normally calibrated to within 0.000020 of an inch (0.00051 mm). The method by which this measurement is made and coupled with the geometrical characteristics of the thread form easily inc
29、reases the resulting uncertainty to 0.000060 of inch (0.001 51 mm). Consideration has also been given to the gage block variations. The variation of the block combination is transferred direct to the measuring device (measuring machine) during initial set up. measured between any two threads over th
30、e length of engagement. AMUa is the measurement uncertainty value in Table I or 2. (b) Diametrical equivalent for lead measurement uncertainty is obtained by multiplying the uncertainty value by 1.7321. Lead is (c) To determine diametrical equivalent for flank angle measurement uncertainty, use the
31、formula: A d,a= 1.5P (tan AMUa) where NOTES TO TABLES 1 AND 2: (1) Measurement uncertainty values are not estimated for internal thread ring gages below 0.190 in. (5 mm) since measurement is not (2) Flank angle measurements on internal threads are made on casts or with tracing instruments. practical
32、. 4 ESTIMATES OF MEASUREMENT UNCERTAINTY In any measurement process, one normally .compares the characteristics of an artifact or product to the results of a measurement instrument or a device. This compari- son inevitably produces errors, and so one cannot deter- mine with complete certainty the ex
33、act value of the char- acteristic even if the measurement instruments or devices readout value is known exactly (which it is not). Furthermore, most instruments or devices are not per- fectly stable; that is, they may change with time and use. For this reason, one of the most important aspects of an
34、y measurement process is the specification of the extent to which the value or values determined during the process may be in error, i.e., the development of a valid uncer- tainty statement. The errors associated with any measurement process 2 MEASUREMENT UNCERTAINTY FOR 60 DEG. SCREW THREAD GAGE EL
35、EMENT MEASUREMENT (INCH AND METRIC) Upper limit for gagemakers measured Upper limit for users measured value gagemakers measured value t Lower limit for users measured value FIG. 1 GAGE ACCEPTANCE USING MEASUREMENT UNCERTAINTY (NEW AND USED GAGES) fall into one of two categories: random errors and s
36、ys- tematic errors. Random error is related to the precision or degree of reproducibility of a measurement process. Systematic error is simply an unwanted offset or bias, the sign and magnitude of which may be unknown, that is present in the measurement process. The total uncertainty must reflect bo
37、th kinds of errors, and thus it is obtained from an appropriate combination of the best estimates of these two types of errors. The measurement uncertainty values presented in Tables 1 and 2 are the best estimates currently available for the variation in the dimensions of thread gages when the gage
38、characteristics are measured. These variations are inherent in the gage measuring techniques and equip- ment. Measurement uncertainty values for lead and flank angle apply to measurements of variables gage segments or rolls as well as to fixed limit gages. The translation of these variations in gage
39、 sizes to the actual product thread evaluated by the respective gages is not addressed by these paragraphs. No attempt has been made to address the impact of gage size variables on product thread eval- uations for either attribute gaging or variable gaging. Intuitively, it can be assumed that at eac
40、h transfer of the measured characteristic (i.e., from setting plug or ring gage to gage contact), additional uncertainty will be accu- mulated. The measurement uncertainty values are based on the use of laboratory grade instruments, accepted measure- ment techniques, and a temperature span of 66F to
41、 70F (18.9“C to 21.1“C). 5 APPLICATION The application of measurement uncertainty is illus- trated in Fig. 1. Measurement uncertainty values are pro- vided for pitch diameter, lead and flank angles. The gage manufacturer shall make the gage within the applicable tabulated GAGEMAKERS TOLERANCE. Howev
42、er, if the customer measures the gage outside of the gagemakers tolerance but within the USERS VER- IFICATION ZONE, then the gage shall be accepted. When disputes arise between two parties and the aver- age measured value is not acceptable, a third party may be used as agreed upon. Examples: (a) The
43、 two disputing parties agree to make a decision based upon the value determined by a third selected party. (b) The parties agree to make a decision on the aver- age of the measurements of the disputed parties and a third party. (c) Each party picks an outside calibration laboratory to measure the it
44、em and the two outside laboratories pick a third calibration laboratory. The average of the three independent measurements is used. 6 BIBLIOGRAPHY ANSUASQC M1-1987, Calibrating Systems Expression of Uncertainty, NCSL, 1990 3 MEASUREMENT UNCERTAINTY FOR 60 DEG. SCREW THREAD GAGE ELEMENT MEASUREMENT (
45、INCH AND METRIC) Fundamentals of Dimensional Metrology, Ted Bush, Del- Realistic Evaluation of the Precision and Accuracy of mar Publishers, Inc., 1964 Instrument Calibration Systems,” Journal of Research, NBS, 1962 Monographs 149 and 163, NBSIR 76-979 Searching for Zero, American Measuring Tool Manufac- turers Association, 1989 ANWASME B89.1M-1984, Precision Gage Blocks for “Systematic Measurement Errors,”Journal of Quality Length Measurement Technology, 198 1 4
