1、BRITISH STANDARD BS 1936-2: 1991 Incorporating Amendment No. 1 Undercuts and runouts for screw threads Part 2: Specification for ISO metric screw threadsBS1936-2:1991 This British Standard, having been prepared under the direction of the General Mechanical Engineering Standards Policy Committee, was
2、 published under the authorityof the Standards Boardand comes into effect on 29 November 1991 BSI 02-1999 First published August 1970 Second edition November 1991 The following BSI references relate to the work on this standard: Committee reference GME/3 Draft for comment 87/76252 DC ISBN 0 580 1887
3、2 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical Committee GME/3, upon which the following bodies were represented: British Industrial Fasteners Federation
4、 British Railways Board British Turned Parts Manufacturers Association Gauge and Tool Makers Association Ministry of Defence Screw Thread Tool Manufacturers Association Ltd. Society of British Aerospace Companies Ltd. Society of Motor Manufacturers and Traders Ltd. Amendments issued since publicatio
5、n Amd. No. Date Comments 8584 May 1995 Indicated by a sideline in the marginBS1936-2:1991 BSI 02-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 ISO metric external threads 1 3 ISO metric internal threads 4 Appendix A Undercuts and runouts for screw threads for
6、 heavy duty applications 6 Appendix B Lengths of runout for various angles of throat or taper lead 10 Figure 1 Undercut (external thread) 1 Figure 2 Runouts (external thread) 2 Figure 3 Form of undercut (internal thread) 4 Figure 4 Diameter of undercut (internal thread) 4 Figure 5 Runouts (internal
7、thread) 5 Figure 6 Shoulder fillets 7 Figure 7 Recessed fillet 7 Figure 8 Length of runout produced by various angles of lead and throat 8 Table 1 Dimensions of undercuts for ISO metric external threads 1 Table 2 Dimensions of runouts for ISO metric external threads 3 Table 3 Dimensions of runouts a
8、nd undercuts for ISO metric internal threads 4 Table 4 Lengths of runout for various angles of throat or taper lead 10 Publication(s) referred to Inside back coverBS1936-2:1991 ii BSI 02-1999 Foreword This Part of BS 1936 has been prepared under the direction of the General Mechanical Engineering St
9、andards Policy Committee and supersedes BS1936-2:1970 which is withdrawn. This Part ofBS1936 covers the undercuts and runouts for both external and internal threads. For external threads it is technically equivalent to the following standards, published by the International Organization for Standard
10、ization (ISO). ISO 3508-1976, Thread run-outs for fasteners with thread in accordance with ISO261 and ISO 262. ISO 4755-1983, Fasteners Thread undercuts for external metric ISO threads. Undercuts and runouts for internal threads are not covered by any ISO standard and the text of the 1970 edition of
11、BS1936-2 has therefore been retained, with some editorial changes. A full revision will be considered once comparable ISO standards are published. Runouts for high duty threaded fasteners for aerospace applications are the subject of BritishStandardA231, which is identical to ISO3353-1976. The requi
12、rements for unified, Whitworth, B.A. and cycle thread forms are specified in BS1936-1. A British Standard does not purport to include 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 i
13、tself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10, 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
14、 indicated in the amendment table on theinside front cover.BS1936-2:1991 BSI 02-1999 1 1 Scope This Part of BS 1936 specifies requirements for dimensions for form, width and diameter of undercuts and runouts for ISO metric external and internal threads for use in general engineering applications. Th
15、reads may be cut or rolled without the die or tap fouling the component. Recommendations for undercuts and runouts for high duty applications are given in Appendix A. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 ISO metric external threads 2.
16、1 Undercuts The form and dimensions of the undercuts shall be as given in Figure 1 and Table 1. Table 1 Dimensions of undercuts for ISO metric external threads Figure 1 Undercut (external thread) Pitch of thread p Thread diameter d (coarse thread) d g h13 a g 1 b min. g 2max. ( 3p) r mm 0.25 0.3 0.3
17、5 0.4 0.45 0.5 0.6 0.7 0.75 0.8 1 1.25 1.5 1.75 2 2.5 3 3.5 4 4.5 5 5.5 6 mm 1 and 1.2 1.4 1.6 and 1.8 2 2.2 and 2.5 3 3.5 4 4.5 5 6 and 7 8 10 12 14 and 16 18 and 20 and 22 24 and 27 30 and 33 36 and 39 42 and 45 48 and 52 56 and 60 64 and 68 mm d-0.4 d-0.5 d-0.6 d-0.7 d-0.7 d-0.8 d-1 d-1.1 d-1.2 d
18、-1.3 d-1.6 d-2 d-2.3 d-2.6 d-3 d-3.6 d-4.4 d-5 d-5.7 d-6.4 d-7 d-7.7 d-8.3 mm 0.4 0.5 0.6 0.6 0.7 0.8 0.9 1.1 1.2 1.3 1.6 2 2.5 3 3.4 4.4 5.2 6.2 7 8 9 11 11 mm 0.75 0.9 1.05 1.2 1.35 1.5 1.8 2.1 2.25 2.4 3 3.75 4.5 5.25 6 7.5 9 10.5 12 13.5 15 17.5 18 mm 0.12 0.16 0.16 0.2 0.2 0.2 0.4 0.4 0.4 0.4 0
19、.6 0.6 0.8 1 1 1.2 1.6 1.6 2 2.5 2.5 3.2 3.2 a h12 up to and including 3mm thread diameter, h13 thread diameter above 3 mm. Tolerance h13 is used for general applications and coarse series threads. For larger diameters and smaller pitches a reduced tolerance may be desirable. Tolerance h12 is recomm
20、ended for precision engineering. (SeeBS 4500-1 for tolerance values.) b g 1min. based on a minimum transition angle of 30.BS1936-2:1991 2 BSI 02-1999 2.2 Runouts The forms and dimensions of the runouts shall be as given in Figure 2 and Table 2. Figure 2 Runouts (external thread)BS1936-2:1991 BSI 02-
21、1999 3 Table 2 Dimensions of runouts for ISO metric external threads Pitch of the thread p Thread diameter d (coarse thread) x max. a max. Normal a ( 2.5 p) Short b ( 1.25 p) Normal c ( 3 p) Short (2 p) Long d(4 p) mm 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.6 0.7 0.75 0.8 1 1.25 1.5 1.75 2 2.5 3 3.5 4 4.5
22、5 5.5 6 mm 1 and 1.2 1.4 1.6 and 1.8 2 2.2 and 2.5 3 3.5 4 4.5 5 6 and 7 8 10 12 14 and 16 18 and 20 and 22 24 and 27 30 and 33 36 and 39 42 and 45 48 and 52 56 and 60 64 and 68 mm 0.5 0.6 0.75 0.9 1 1.1 1.25 1.5 1.75 1.9 2 2.5 3.2 3.8 4.3 5 6.3 7.5 9 10 11 12.5 14 15 mm 0.25 0.3 0.4 0.45 0.5 0.6 0.
23、7 0.75 0.9 1 1 1.25 1.6 1.9 2.2 2.5 3.2 3.8 4.5 5 5.5 6.3 7 7.5 mm 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.8 2.1 2.25 2.4 3 4 4.5 5.3 6 7.5 9 10.5 12 13.5 15 16.5 18 mm 0.4 0.5 0.6 0.7 0.8 0.9 1 1.2 1.4 1.5 1.6 2 2.5 3 3.5 4 5 6 7 8 9 10 11 12 mm 0.8 1 1.2 1.4 1.6 1.8 2 2.4 2.8 3 3.2 4 5 6 7 8 10 12 14 16
24、18 20 22 24 a Runout x normal for all types of screws in product grades A, B and C. b Runout x short only in cases where a short runout is required for technical reasons. c Distance a normal for all types of screws in product grade A. d Distance a long for all types of screws in product grades B and
25、 C.BS1936-2:1991 4 BSI 02-1999 3 ISO metric internal threads 3.1 Undercuts The form and dimensions of the undercuts shall be as given in Figure 3 and Figure 4 and columns6 to10 of Table 3. 3.2 Runouts The form and dimensions of the runouts shall be as given in Figure 5 and columns3to5 of Table 3. Ta
26、ble 3 Dimensions of runouts and undercuts for ISO metric internal threads Figure 3 Form of undercut (internal thread) Figure 4 Diameter of undercut (internal thread) 1 2 3 4 5 6 7 8 9 10 Pitch P Thread diameter D (coarse thread) Runout (min.) Undercut (max.) R Diameter DG H13 b Long a X 1 Medium X 2
27、 Short X 3 Long F 1= 6P Medium F 2= 4P Short F 3= 2P mm 0.25 0.3 0.35 mm M1 and 1.2 M1.4 M1.6 and 1.8 mm mm 1.30 1.60 1.70 mm mm mm mm mm mm 0.4 0.45 0.5 M2 M2.2 and 2.5 M3 2.60 3.40 3.80 1.80 2.50 2.80 1.40 1.68 2.00 3.00 2.00 1.00 3.50 D + 0.3 0.6 0.7 0.75 M3.5 M4 M4.5 4.40 4.80 5.00 3.00 3.40 3.5
28、0 2.10 2.45 2.52 3.60 4.20 4.50 2.40 2.80 3.00 1.20 1.40 1.50 0.50 0.60 0.60 D + 0.3 D + 0.3 D + 0.3 0.8 1 1.25 M5 M6.7 M8 5.20 6.50 7.50 3.60 4.50 5.00 2.60 3.10 3.48 4.80 6.00 7.50 3.20 4.00 5.00 1.60 2.00 2.50 0.60 0.80 1.00 D + 0.3 D + 0.5 D + 0.5 1.5 1.75 2 M10 M12 M14 and 16 8.50 9.50 10.50 5.
29、50 6.00 6.50 3.85 4.22 4.60 9.00 10.50 12.00 6.00 7.00 8.00 3.00 3.50 4.00 1.00 1.00 1.20 D + 0.5 D + 0.5 D + 0.5 2.5 3 3.5 M18 and 20 and 22 M24 and 27 M30 and 33 12.50 14.50 17.00 7.50 8.50 10.00 5.35 6.10 7.25 15.00 18.00 21.00 10.00 12.00 14.00 5.00 6.00 7.00 1.60 2.00 2.00 D + 0.5 D + 0.5 D + 0
30、.5 4 4.5 5 M36 and 39 M42 and 45 M48 and 52 18.00 21.00 23.00 11.00 12.00 13.00 8.00 8.75 9.50 24.00 27.00 30.00 16.00 18.00 20.00 8.00 9.00 10.00 2.00 2.50 2.50 D + 0.5 D + 0.5 D + 0.5 5.5 6 M56 and 60 M64 and 68 26.00 28.00 15.00 16.00 11.25 12.00 33.00 36.00 22.00 24.00 11.00 12.00 3.00 3.00 D +
31、0.5 D + 0.5 a The long runout dimensions specified avoid the use of bottoming taps. These dimensions are to be used for production machine tapping. b For larger diameters and smaller pitches a reduced tolerance may be necessary (see BS 4500-1 for tolerance values).BS1936-2:1991 BSI 02-1999 5 Figure
32、5 Runouts (internal thread)BS1936-2:1991 6 BSI 02-1999 Appendix A Undercuts and runouts for screw threads for heavy duty applications A.1 General The recommendations in A.2 to A.9 are intended to apply to threaded components subjected to substantial fatigue or impact loads. A.2 Stress concentration
33、It is important that the stress concentration at a runout or undercut is not unduly high. Sharp corners should therefore be avoided, particularly when associated with a pronounced change of section. A.3 Thread runouts onto a plain shank of not more than the nominal thread diameter In the case of a t
34、hread runout used on a plain shank the diameter of which is not more than the thread nominal diameter, the change of section is small. In critical cases it is nevertheless desirable to avoid sharp corners at the roots of the partial threads composing the runout; the crests of the chamfered threads o
35、n the threading tool should be rounded so that the resulting radii produced on the part are not less than the minimum root radius specified for the complete thread. A.4 Thread runouts close to a pronounced change of section Runouts should not occur close to a pronounced change of section, e.g. in st
36、uds, tie-bars, shafts or rollers with threaded extensions of smaller diameter. Where it is necessary to screw on the mating component as far as the shoulder, an undercut should preferably be employed as in Figure 6(b) (for J seeA.6 and A.9). If it is necessary to run out the thread onto a full diame
37、ter shank, a counterbore or spacing sleeve should be used as inFigure 6(a) to enable the runout to be terminated far enough from the shoulder to permit an adequate transition radius (seeA.6 and A.9) and to avoid superposition of the stress concentrations due to the two features; an interval P or0.5J
38、 whichever is the greater, between the end of the runout and the blend of the shoulder fillet with the smaller diameter shaft, will be sufficient to achieve this, giving W $ 1.5J + X, or W $ J + P + X, whichever is the greater, where X is the length of the thread runout (seeFigure 8). Contact with t
39、he sleeve or counterbored component in the region of the shaft fillet should be avoided because of possible fatigue strength reduction due to fretting seeFigure 6(a). A.5 Transition radius, thread end At the thread end of an undercut, the transition radius should be not less than the thread root rad
40、iusJ=0.15p. A.6 Transition radius, shoulder end At the shoulder end of an undercut, or at a shoulder coming close to a runout as inFigure 6, the transition radius required, calculated from A.9, will depend on the severity of the change of section and on the magnitude of the fatigue strength reductio
41、n due to the thread. The latter factor 1)is unlikely to be less than4.5 for machine threads or 2.25 for rolled threads. When the mean stress is zero, the stress concentration factor at the shoulder end of the undercut need only, therefore, be less than the respective values. “Rolled” threads in this
42、 context are those that are not heat-treated after rolling. Stress concentration factors for fillets may be obtained from Engineering Sciences Data ItemNo.89048 or from Peterson, R.E., “Stress Concentration Design Factors”, John Wiley, NewYork. It may be noted that, if J is not less than0.05d (seeFi
43、gure 6), then so long as D is not more than1.3d, the fillet stress concentration factor will not exceed2.25; also that, even for D = 2d, the stress concentration factor will only attain a value of4.5 for values of J less than about0.02d. Actual fatigue strength reduction factors will not be higher t
44、han the theoretical factors, provided that the fillet form and surface finish are adequate, particularly in the region where the transition radius blends smoothly with the shaft of diameter d. When the mean stress is appreciably greater than zero, the above values for the fillet stress concentration
45、 factor may be unsafe and values of3for fillets to be used with machined threads or1.5 for fillets to be used with rolled threads are recommended. 1) Referred to as the fatigue strength of plain polished bars at zero mean stress.BS1936-2:1991 BSI 02-1999 7 A.7 Surface roughness In order to avoid red
46、uction in fatigue strength due to surface roughness, the latter should be, for heat-treated steels, not more than about2mm peak-to-valley, i.e.0.5mm centreline average and2mm Ra (seeBS1134); for annealed or normalized steels of up to about 600 N/mm 2tensile strength, these values can be doubled. Dou
47、bling them for either group of steels will reduce the fatigue strength by a factor of about1.2; this should be multiplied by the fillet stress concentration factor to give the overall value. The finish should be as uniform as possible; isolated deep machining marks can have a serious adverse effect
48、on fatigue strength. A.8 Recessing If it is not practicable to provide a large enough radius of the normal type, recessing can be used (seeFigure 7). Alternatively, the fatigue strength can be increased by fillet rolling, as described inSAEJ811, “Surface rolling and other methods for mechanical pres
49、tressing of metals”, Soc. Automotive Engrs., 485 Lexington Ave., NewYork17, N.Y., June1962. Other surface strengthening processes, e.g.nitriding or induction hardening, may sometimes be suitable, though the effects of these are less localized. Figure 6 Shoulder fillets Figure 7 Recessed filletBS1936-2:1991 8 BSI 02-1999 A.9 Determination of J, the transition radius at the shoulder, when a mean tensile stress is applied A.9.1 Estimation of permissible nominal stress at the shoulder fillet When the threaded
