B01.09

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c AREA THDS COPYRIGHT American Society of Mechanical Engineers Licensed by Information Handling Services . ASME B I - 7 73 W 2 5 7 5 5 3 2 0 3 2 3 3 3 0 O W A M E R I C ANNA T I O N A L A N D A R D ST Buttress Inch Screw Threads 7y45 Form With 0.6 Pitch Basic Height .of Thread Engagement b- ANSI B1.9~1973 SECRETARIAT THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS i PUBLISHED BY THE MERICAN OCI.ETY A S United Engineering Center OF MECHANICAL ENGINEERS 3 4 5 E a s t 47th Street New
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  c AREA THDS . COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services  b- ASME BI-7 73 W 2575532 032333 O W AMERICANATIONALTANDARD Buttress Inch Screw Threads 7y45 orm With 0.6 Pitch Basic Height .of Thread Engagement ANSI B1.9~- 973 SECRETARIAT THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS i PUBLISHED BY THEAMERICAN OCI.ETY OF MECHANICAL ENGINEERS Unitedngineering enter 345 East 47th treet ew York, N. Y. 1 O01 7 COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services  No part of this document may be reproduced in any form, in anelectronic retrieval system or otherwise, without the prior written permis-sion of the publisher. Copyright O 1974 by -THEAMERICAN SOCIETY OF MECHANICAL ENGINEERS Printed in U.S.A. COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services  ASME BI-7 73 m 2575532 00112335 4 m FOREWORD Although the buttress thread was described as early as the March, 1888, Journal of the Franklin In-stitute, it was so little used that its national standardization was not undertaken until after the CombinedConservation Committee in early 1942 reviewed the standardization status of items needed in- the war ef-fort. Formerly each application of the buttress thread was treated individually and the form it took de-pended on the experience of the designer and the manufacturing equipment available.should be established for this thread. As the Military Departments needed buttress and other special typesof threads, the War Production Board in February, 1944, arranged with the ASA toestablish a General War'Committee on Screw Threads.The Interdepartmental Screw Thread Committee (ISTC) agreed to develop a buttress thread formhaving a pressure flank angle of 7 deg, which closely approaches the static angle of friction for well lubri-cated steel surfaces in contact,and a clearance flank angle of 45 deg.The British agreed to prepare and circulate a draft specification for an asymmetrical buttress threadhaving a 7 deg load flank angle, a 45 deg clearance flank angle, and a basic height of thread engagement of 0.4 pitch.The 1944 edition of Handbook H28 published the ISTC's recommendation of a basic buttress threadform which had a crest flat in the nut twice that of the screw, and a thread engagement height of approxi-mately 0.56~. n November 1944, the ASA War Subcommittee on Buttress Threads was established andafter reviewing the British draft of April 1945, this committee felt that because of the distortion tendencyof thin wall tubing, a greater basic height of thread engagement than 0.4~ as desirable, especially since theminimum height of thread engagement is necessarily less than 0.4~y one-half the sum of the allowanceand the tolerances on minor diameter of internal thread and major diameter of external thread. Therefore,the July 1945 draft f the War Standard was based on a basic height of thread engagement of 0.5~. Another American-British-Canadian conference sponsored by the Combined Production and Re-sources Board was held h Ottawa, Canada, September-October 1945. Here the British proposal of April1945, with an alternate design of O deg pressure flank angle and a trailing flank angle of 52 deg, was re-viewed and compared with the American proposal of July 1945. Learning that the British had had con-siderable favorable experience on thin wall tubing with buttress threads having 0.4~asic height of threadengagement, it was decided that the American standard might adopt this basis. Accord was also reached onpreferred diameters and pitches, thread dimension tolerances and allowances, and on having each standardinclude in its appendix an alternate hread of O degree.pressure flank angle. Further, each country agreed topublish the. standard in conformance with their respective formats.In April 1946, buttress threads were assigned to Subcommittee No. 3 of the Sectional Committee onthe Standardization and Unification of Screw Threads, B1, and the committee membership was enlarged. This committee prepared and circulated in 1948 to members of the B1 committee a draft of a proposedstandard based on the British proposal with a basic thread height of 0.4~. he comments included so manyobjections to the shallow height of thread that in 1949 the committee decided to base the next draft on athread having 0.6~ngagement height. The committee also voted not to include in the appendix of theAmerican standard data for a buttress thread having O deg pressureflank angle as it was.evident that this wasonly one of several modifications that might be needed for special applications. The next American-British-Canadian conference was called at the request of the Director of DefenseMobilizafion and held in New York, June 1952. The British Standard 1657: 1950 for Buttress Threadswhich is based on a thread engagement height of 0.4~ nd the American draft of September 195 1, based onthread engagement height of 0.6p, were reviewed. It was concluded that the applications for buttressthreads are so varied that threads with either engagement height (0.4~ r 0.6~) ight be preferred forparticular design requirements. It was recommended that the next printing of the British standard and theforthcoming American standard include the essential details of the other country's standards in appendixes.ASA B1.9-1953, Buttress Screw Threads, was issued in conformance with this recommendation. This 1973 Revision of B1.9 is being issued to bring the standard into conformance with presentpractices. The three classes of threads have been reduced to two-Class 2 (standard grade) and Class 3 (precision grade).Following approval by the Sectional Committee of B1, and the Secretariats, the revised standard wassubmitted to the American National Standards Institute for approval. This approval was granted on October ' 22, 1973.At he American-British-Canadian conference New York, in 1943, hey agreed that a basic profile . iii COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services
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