1、BRITISH STANDARD BS 3777:1964 Incorporating Amendment No. 1 Specification for Screw thread measuring cylindersBS3777:1964 This British Standard, having been approved by the MechanicalEngineering IndustryStandards Committee and endorsed by the Chairman ofthe Engineering Divisional Council, was publis
2、hedunder theauthorityofthe GeneralCouncil on 17August1964 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference MEE/59 Draft for comment D62/35 ISBN 0 580 036987 Co-operating organizations The Mechanical Engineering Industry Standards Committee, under whos
3、e supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Association of Consulting Engineers Association of Mining Electrical and Mechanical Engineers Br
4、itish Chemical Plant Manufacturers Association British Compressed Air Society British Electrical and Allied Manufacturers Association British Gear Manufacturers Association British Internal Combustion Engine Manufacturers Association British Iron and Steel Federation British Mechanical Engineering F
5、ederation British Railways Board Crown Agents for Oversea Governments and Administrations D.S.I.R.-National Engineering Laboratory Electricity Council, the Generating Board and the Area Boards in England and Wales Engineering Equipment Users Association Gas Council High Commission of India Institute
6、 of Marine Engineers Institute of Petroleum Institution of Civil Engineers Institution of Gas Engineers Institution of Heating and Ventilating Engineers Institution of Mechanical Engineers Institution of Mechanical Engineers (Automobile Division) Institution of Production Engineers Locomotive and Al
7、lied Manufacturers Association of Great Britain London Transport Board Machine Tool Trades Association Ministry of Defence, Army Department Ministry of Defence, Navy Department Ministry of Labour (H.M. Factory Inspectorate) Ministry of Power Ministry of Transport Ministry of Public Building and Work
8、s National Coal Board National Physical Laboratory (D.S.I.R.) Radio Industry Council Royal Institute of British Architects Amendments issued since publication Amd. No. Date Comments 2656 July 1978 Indicated by a sideline in the marginBS3777:1964 BSI 11-1999 i Contents Page Co-operating organizations
9、 Inside front cover Foreword ii 1 Scope 1 2 Terminology 1 Part 1. Grades of cylinders 3 Tolerances and P values 1 4 Relative merits of Grade A and Grade B screw thread measuring cylinders 2 Part 2. Specification for thread measuring cylinders 5 Measuring range 2 6 Material and finish 2 7 Form and ge
10、neral dimensions 2 8 Accuracy 4 9 Identification 5 10 Container 5 Figure 1 Thread measuring cylinder 3 Figure 2 Testing straightness of cylinders 4 Figure 3 Identification tags 5 Table 1 Range of screw threads 2 Table 2 Recommended overall lengths 3 Table 3 Nominal diameters and associated P values
11、of Grade A (pitch-line) cylinders for Unified and ISO inch threads 6 Table 4 Nominal diameters and associated P values of Grade A (pitch-line) cylinders for Whitworth threads 7 Table 5 Nominal diameters and associated P values of Grade A (pitch-line) cylinders for ISO Metric threads 8 Table 6 Nomina
12、l diameters and associated P values of Grade A (pitch-line) cylinders for B.A. threads 8 Table 7 Limits of size for Grade B (grouped) cylinders 9 Table 8 Formulae on which the diametrical limits for Grade B cylinders are based 10BS3777:1964 ii BSI 11-1999 Foreword This standard makes reference to th
13、e following British Standards: BS 84, Parallel screw threads of Whitworth form. BS 93, British Association (B.A.) screw threads. BS 427, Vickers hardness test Part 1:1961 Testing of metals. BS 1580, Unified screw threads. BS 3643, Metric screw threads. This British Standard which relates to screw th
14、read measuring cylinders, used in the determination of the effective diameter E of external screw threads, has been prepared under the authority of the Mechanical Engineering Industry Standards Committee in response to requests from the National Physical Laboratory and from user sources. Thread meas
15、uring cylinders have been employed in the measurement of external screw threads for many years and their use for this purpose has long been familiar. During World War I the National Physical Laboratory established a recommended series of so-called “Best-size” cylinders for use in the measurement of
16、screw threads of Whitworth, ISO Metric and B.A. thread forms. This series, amended and enlarged to include Unified threads, has been used extensively ever since and is still in use in this country at the present time. In issuing this first British Standard for screw thread measuring cylinders opport
17、unity has been taken to draw on the considerable experience gained in screw thread measurement over the years. Two grades of measuring cylinders are provided for in the standard, viz., Grade A (pitch-line) cylinders and Grade B (grouped) cylinders. Grade B cylinders are the same as the N.P.L. “Best-
18、size” cylinders referred to above; Grade A cylinders are new and are chosen to make contact with the flanks of the screw thread under measurement very close to the pitch-line. This entails a particular size of Grade A cylinder for each form and pitch of screw thread. SPECIAL NOTE. The introduction o
19、f Grade A (pitch-line) cylinders with their finer diametral tolerances renders the term “Best-size” (as applied to the series originally covered by the N.P.L. Schedule) anomalous, and the designation “Best-size” is therefore not recognized in this standard. A British Standard does not purport to inc
20、lude all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, page
21、si and ii, pages1to10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS3777:1964 BSI 11-1999 1 1 Scope This British Standard relates to two g
22、rades of screw thread measuring cylinders intended for use in checking external screw threads by means of pitch diameter measuring machines. NOTEFor a full description of this well established method of measuring the effective diameter of an external screw thread when using thread measuring cylinder
23、s, and also for an explanation of the P value used in this measurement, see “Notes on Applied Science No.1” issued by the Department of Scientific and Industrial Research and entitled “Gauging and Measuring Screw Threads”, published by Her Majestys Stationery Office. The standard comprises two parts
24、: Part1 gives the bases for the diametral tolerances of Grade A and Grade B screw thread measuring cylinders and the relative merits of the two grades. Part2 gives the complete specification for both grades of cylinders suitable for the forms and pitches of screw threads shown inTable 1. 2 Terminolo
25、gy “Pairs” and “sets” of screw thread measuring, cylinders. When two cylinders are used for measuring the effective diameter of a screw thread they are referred to in this standard as a “pair” and when three cylinders are used they are referred to as a “set”. Part1. Grades of cylinders 3 Tolerances
26、and P values a) Grade A (pitch-line) screw thread measuring cylinders. Grade A cylinders nominally make contact with the flanks of the screw thread on the pitch line; it follows that a pair (or a set) will be required for each pitch and form of screw thread to be measured. A diametral tolerance of 0
27、.000 02 in from nominal size is allowed. It is intended that the P value associated with Grade A cylinders should be calculated on the nominal diameter of the cylinders used, regardless of where their actual diameters lie within the 0.000 02 in tolerance zone. NOTEShould the actual diameters of a pa
28、ir or set of Grade A cylinders all happen to fall on the upper or on the lower limit of the 0.00002 in tolerance zone, then the basing of the P value on the nominal diameter of the thread measuring cylinder could give rise to an error of0.00002 inches in the measured effective diameter of Whitworth,
29、 Unified and ISOMetric threads, and0.00003 inches in the case of B.A. threads. These small inaccuracies of measurement. which only occur in extreme cases, are considered to be insignificant; they could of course bc entirely eliminated, if desired, by calculating the P value using the actual mean dia
30、meter of the thread measuring cylinders instead of the nominal diameter. b) Grade B (grouped) screw thread measuring cylinders (original N.P.I. “Best-size” cylinders). Grade B cylinders have larger diametral tolerances than those of Grade A to enable an individual pair or set to be used for measurin
31、g a specified range of screws of different form and pitch. Their diametral tolerances are controlled, so as to allow them to make contact with the flanks of the thread anywhere within a distance on each side of the pitch-line equal to one-twentieth of the length of the straight portion of the flank.
32、 (This requirement is modified slightly for screw threads of Unified and ISO Metric form; for these threads the cylinders make contact with the flanks anywhere within a distance on each side of the pitch line equal to one-tenth of the length of the straight portion above the pitch-line.) Calculating
33、 the diametral tolerance zones on the above basis for cylinders to be used on threads of Whitworth, Unified, ISO Metric and B.A. forms, reveals that the zones for some thread, forms overlap. Thus it is possible to select a restricted tolerance zone which is common for threads of different form which
34、 can be served by a single pair (or set) of cylinders. The details relating to Grade B cylinders given in Table 7 have been worked out on this basis. Sometimes a pair or set of Grade B cylinders is purchased for the measurement of a screw thread of one form only. In this case the permitted diametral
35、 tolerance band for the cylinders is calculated for the particular form of screw thread in question, using the appropriate formula given inTable 8. The P value to be associated with a pair or set of Grade B cylinders is calculated on the mean of the measured diameters of the two or three cylinders c
36、oncerned. When Grade B cylinders are used to measure a screw thread whose flank angles are in error by as much as the full equivalent of the tolerance allowed on the effective diameter of the thread, the error which could arise in measuring the effective diameter (on the assumption that the flank an
37、gles were correct) could, in the extreme case, be about one-tenth of the tolerance allowed on that diameter.BS3777:1964 2 BSI 11-1999 4 Relative merits of Grade A and GradeB screw thread measuring machines The choice between Grade A and Grade B cylinders will depend on the nature and variety of the
38、screw thread measurements to be undertaken. The following assessment of the relative merits of the two grades is included in the standard to help the purchaser in making his choice. With Grade A cylinders, a pair (or set) of cylinders is required for each pitch and form of screw thread to be measure
39、d. On the other hand, with Grade B cylinders, 30pairs (or sets) will serve to measure the entire range of screw threads of the forms mentioned in Clause5 having pitches ranging from3 to80 t.p.i. (or8mm to0.35 mm). Should the user be interested in a wide range of screw threads then, on economic groun
40、ds, Grade B cylinders would be preferred to Grade A. Grade A cylinders possess certain advantages over Grade B cylinders. These include: a) Freedom from the effects of flank angle errors. The measured effective diameters obtained with Grade A cylinders are not influenced by flank angle errors and th
41、ese cylinders therefore give, in general, a slightly enhanced accuracy of measurement as compared with Grade B cylinders. b) Simplicity of replacement and constancy of P value. The replacement of a Grade A cylinder due to loss, breakage or wear, does not necessitate any change in the P value of the
42、particular pair or set since this value is based on the nominal diameter of the cylinders and is therefore constant for all certified cylinders intended for use with one particular thread form and pitch. c) Ease of identification. Separate identification of Grade A cylinders is not important; it is
43、only necessary to indicate on the identification disk the thread form and pitch of the screw for which a Grade A cylinder is required. The allocation of serial numbers to individual Grade A cylinders is not necessary. Part 2. Specification for thread measuring cylinders 5 Measuring range The Grade A
44、 and Grade B cylinders covered by this standard are intended for use on screw threads of the forms and pitches given inTable 1. The cylinders may be used in pairs or sets. NOTEA pair of cylinders can only be used when the measurement is constrained to be at right angles to the axis of the screw thre
45、ad, as is the case with the N.P.L. type of “floatingdiameter” measuring machine. Table 1 Range of screw threads 6 Material and finish Thread measuring cylinders shall be made of steel and shall be hardened. To avoid brittleness and breakages in use, a hardness value of about700 HV is recommended. NO
46、TEDetails of a suitable method of measuring the hardness of cylinders are given in Appendix B of BS427, “Vickers hardness test”, Part 1:1961, “Testing of metals”. The working surface shall have a lapped finish, free from any blemishes such as scratches, pits and rust stains. 7 Form and general dimen
47、sions a) Form. The general form of the cylinders shall be as shown inFigure 1. b) Overall length. Recommended approximate overall lengths L of screw thread measuring cylinders are given inTable 2. Screw thread system a Range Unified and ISOinch (60 ) From4 t.p.i. to80t.p.i.inc. Whitworth (55 ) From
48、3 t.p.i. to40t.p.i.inc. ISO metric (60 ) From 8 mm pitch to0.35mm pitch inc. BA (47 1 / 2 ) From 0 BA to10BA inc. a Details of these threads are given in the following BritishStandards: BS 84, “Parallel screw threads of Whitworth form”. BS 93, “British Association (B.A.) screw threads”. BS 1580, “Un
49、ified screw threads”. BS 3643, “Metric screw threads”.BS3777:1964 BSI 11-1999 3 c) Working length. The working length l is defined as that part of the overall length beginning at a distance of not more than0.1 inch from below the part of the cylinder having a cap or hole and ending at a distance of not more than0.1 inch from the other end of the cylinder. (SeeFigure 1.) The requirements for accuracy and hardness shall apply to the working length as defined above. Table 2 Recommended overall lengths Figure 1 Thread measuring cylinder Di
