1、BRITISH STANDARD BS5590:1978 Incorporating Amendment No. 1 Specification for Screw thread metric series measuring cylinders UDC621.882.082.1:531.717.15BS5590:1978 This British Standard, having been prepared under the direction of the Mechanical Engineering Standards Committee, was published under th
2、e authority of the Executive Board on 31 May1978 BSI07-1999 The following BSI references relate to the work on this standard: Committee reference MEE/59 Draft for comment73/33654 DC ISBN 0 580 35087 8 Cooperating organizations The Mechanical Engineering Standards Committee, under whose direction thi
3、s British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Department of Trade (Marine Division) Association of Consulting Engineers Department of Transport Association of
4、Hydraulic Equipment Electricity Supply Industry in England Manufacturers and Wales Association of Mining Electrical and Engineering Equipment Users Association Mechanical Engineers Federation of Manufacturers of British Compressed Air Society Construction Equipment and Cranes British Electrical and
5、Allied Manufacturers Health and Safety Executive Association (BEAMA) Institution of Gas Engineers British Gas Corporation Institution of Mechanical Engineers British Gear Manufacturers Association Institution of Plant Engineers British Internal Combustion Engine Institution of Production Engineers*
6、Manufacturers Association London Transport Executive British Pump Manufacturers Association Machine Tool Trades Association British Steel Corporation Ministry of Defence* British Steel Industry National Coal Board Chartered Institution of Building Services Process Plant Association Crown Agents for
7、Oversea Governments and Railway Industry Association of Administrations Great Britain Department of the Environment Society of Motor Manufacturers and Department of Industry Traders Limited (Mechanical Engineering) Telecommunication Engineering the mean measured diameter of each cylinder; the design
8、ation (see Table 2 and Table 4); the P value, or values, corresponding to the use of the pair or set to the thread forms and pitches of screw threads listed in Table 2, Table 3 and Table 4 as appropriate. 10 Replacement cylinders When a cylinder is lost, broken or otherwise damaged, an appropriate r
9、eplacement cylinder may be substituted, provided that the P value is recalculated according to the mean diameter of the cylinders in the reconstituted pair or set. 11 Use of designated cylinders for other thread forms The application of the cylinders listed in Table 2 for measuring the pitch diamete
10、r of Unified, Whitworth and B.A. screw threads, is given in Appendix C , Table 3. Additional cylinders required for such screw threads not included in Table 3 are given in Table 4. Figure 2 Testing straightness of cylindersBS5590:1978 4 BSI 07-1999 Appendix A Definitions of pitch, pitch diameter and
11、 pitch line A.1 pitch the distance measured parallel to the axis between corresponding points on adjacent thread forms A.2 pitch diameter the diameter of an imaginary cylinder which intersects the surface of the thread in such a manner that the intercept on a generator of the cylinder between the po
12、ints where it meets the opposite flanks of the thread groove is equal to one half of the nominal pitch of the thread (see Figure 3) A.3 pitch line the line of the generator making the intercepts with the flanks defining pitch diameter (seeFigure 3) Appendix B Derivation of P value Note3 to3.1 refers
13、 to a full description of the method of measuring the pitch diameter of a screw thread, but for convenience of reference brief details are given below. B.1 Dimension T. A micrometer reading is obtained over cylinders contacting a plain setting plug of known diameter after which readings are taken ov
14、er the same cylinders contacting the flanks of the screw thread. Thus, dimension T is obtained, see Figure 4. Figure 3 Pitch diameter and pitch line of a screw threadBS 5590:1978 BSI 07-1999 5 Figure 4 Use of two cylinders to measure a screw thread to obtain dimension T Figure 5 Cylinder contact and
15、 relationship to E, T and P valuesBS5590:1978 6 BSI 07-1999 B.2 E, T and P value (see Figure 5) If E = measured pitch diameter T = measured dimension under the cylinders p = nominal pitch of thread w = mean measured diameter of cylinders used ! = flank angle of thread. Then E = T + w w cosec !+cot !
16、 Since the nominal values of p, cosec ! and cot !, together with the value of w are known before measurement, they can be gathered into a single value called the P value, i.e.for a given diameter of cylinder, w, in a given thread form of flank angle ! and pitch p P value = p cot ! (cosec ! 1) w and
17、E = T + P value By substituting the appropriate values of cosec ! and cot ! in the equation for P value, a general expression can be obtained for the P value of each thread form as follows. Appendix C Use of designated cylinders for various thread forms C.1 Designated cylinders in Table 2 can also b
18、e used for certain pitches of Unified, Whitworth and B.A. thread forms as shown in Table 3. In these additional applications the designated cylinders do not contact the pitch line. However, the P value ascribed to a pair of cylinders for the different threads concerned may be used to measure threads
19、 having errors of included flank angle of up to the amounts specified below without thereby introducing an error greater than0.0005mm. Where the included angle of a thread exceeds the above departures, the following formulae may be used to derive the correction to apply to the P value which has been
20、 calculated, assuming the included angle is nominal. ISO metric : P value = 0.866025 p w Unified : P value = 0.866025 p w Whitworth : P value = 0.960491 p1.165681 w B.A. : P value = 1.136336 p1.482950 w Unified and Whitworth (t.p.i.) B.A. no. Maximum departure from nominal included flank angle 4 to8
21、 10 to19 20 to32 36 to44 56 to72 2 and3 6 7 and8 11 15 ( ) 0.15 0.3 0.5 0.7 1.0 1.2 1.8 2.5 Form of thread Correction to P value Unified (0.0302w 0.0175p) (2a) Whitworth (0.0363w 0.0205p) (2a) B.A. (0.0492w 0.0269p) (2a) where w is the mean diameter of cylinders used (in mm) p is the pitch of thread
22、 (in mm) (2a) is the departure from nominal included angle, expressed as degrees p 2 -BS 5590:1978 BSI 07-1999 7 NOTEThis correction must be added to the P value, if the value of (2a) is positive, i.e.for an angle larger than nominal, and subtracted if (2a) is negative. C.2 Additional cylinders requ
23、ired for screw threads not included in Table 3 are listed in Table 4. In each case, the nominal size cylinders recommended are based on pitch line contact except where Unified and Whitworth form are grouped in which case the cylinder recommended contacts the pitch line of the Unified thread. Table 3
24、 Screw threads for which designated metric cylinders are also suitable Designated metric cylinder Nominal diameter Designated metric cylinders in cols.1 and2 are also suitable for: Unified Whitworth B.A. no. (pitch) 5.5p 5p 4p 3.5p 3p 2.5p 2p 1.75p 1.5p 1.25p 1p 0.8p 0.75p 0.7p 0.6p 0.5p 0.45p 0.4p 0.35p 0.3p 0.2p mm 3.1754 2.8868 2.3094 2.0207 1.7320 1.4434 1.1547 1.0104 0.8660 0.7217 0.5774 0.4619 0.4330 0.4041 0.3464 0.2887 0.2598 0.2309 0.2021 0.1732 0.1155 t.p.i. 4 5 7 8 10 13 14 16, 18 20 32 32 36 40, 44 56 64 72 80 t.p.i. 4 5 6 7 8 10 12 14 16 19, 20 24, 26 32 32 36 40 2 3 6 7 8 11 15
