1、BS 939:2007Engineers squares (including cylindrical and block squares) SpecificationICS 25.060.01NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document w
2、as last issued. BSI 2007ISBN 978 0 580 58628 6The following BSI references relate to the work on this standard:Committee reference MTE/1Draft for comment 07/30163789 DCPublication historyFirst published January 1941First revision, November 1962Second revision, September 1977Third revision, October 2
3、007Amendments issued since publicationAmd. no. Date Text affectedBS 939:2007 BSI 2007 iBS 939:2007ContentsForeword iiiSection 1: General 11 Scope 12 Normative references 13 Terms and definitions 14 Protection against climatic conditions 2Section 2: Engineers try squares 35 Designating size 36 Recomm
4、ended sizes 37 Material and manufacture 48 General features of design 49 Finish 410 Accuracy 511 Rigidity 912 Marking 9Section 3: Cylindrical squares 1013 Designating size 1014 Recommended sizes and dimensions 1015 Material and manufacture 1116 General features of design 1117 Finish 1218 Accuracy 12
5、19 Marking 13Section 4: Solid form block squares 1420 Designating size 1421 Recommended sizes and dimensions 1422 Material and manufacture 1523 General features of design 1524 Finish 1625 Accuracy 1626 Marking 17Section 5: Open form block squares 1827 Designating size 1828 Recommended sizes and dime
6、nsions 1829 Material 1930 General features of design 1931 Finish 1932 Accuracy 1933 Marking 20AnnexesAnnex A (informative) Notes regarding bevelled edges on blades of grade AA engineers try squares 21Annex B (informative) Notes on the manufacture and testing of squares 25Bibliography 26BS 939:2007ii
7、 BSI 2007List of figuresFigure 1 Exaggerated illustration of deviation from squareness and squareness tolerance 2Figure 2 Engineers try squares 3Figure 3 Squareness of blade edges to working faces of stock 8Figure 4 Lateral squareness of blade 8Figure 5 Rigidity 9Figure 6 Nomenclature for cylindrica
8、l squares 10Figure 7 Nomenclature for solid form block squares 14Figure 8 Nomenclature for open form block squares 18Figure A.1 Using a bevelled edge 21Figure B.1 Method of testing squareness of block squares 23Figure B.2 Tilting tester 24Figure B.3 Testing for rigidity 25List of tablesTable 1 Toler
9、ances on straightness of blade edges 5Table 2 Tolerances on parallelism of blade edges 5Table 3 Tolerances on flatness of working faces of stock 6Table 4 Tolerances on parallelism of working faces of stock 6Table 5 Tolerances on parallelism of side faces of stock 6Table 6 Tolerances on squareness of
10、 blade edges to working faces of stock 7Table 7 Tolerance on lateral squareness of blade to base of stock 8Table 8 Recommended sizes and dimensions of cylindrical squares 10Table 9 Tolerances on cylindrical squares 12Table 10 Recommended sizes and dimensions of solid form block squares 14Table 11 To
11、lerances on flatness, parallelism and squareness of working faces (solid iron block squares) 16Table 12 Tolerances on flatness and squareness of front and back surfaces (solid iron block squares) 16Table 13 Recommended sizes and dimensions of open form block squares 18Table 14 Tolerances on flatness
12、, parallelism and squareness of working faces (open form block squares) 20Table 15 Tolerances on flatness and squareness of front and back surfaces (open form block squares) 20Summary of pagesThis document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 26, an inside back c
13、over and a back cover. BSI 2007 iiiBS 939:2007ForewordPublishing informationThis British Standard is published by BSI and came into effect on 31 October 2007. It was prepared by Technical Committee MTE/1, Machine tools. A list of organizations represented on this committee can be obtained on request
14、 to its secretary.SupersessionThis British Standard supersedes BS 939:1977, which is withdrawn.Information about this documentThis is a full revision of the standard.Presentational conventionsThe provisions of this standard are presented in roman (i.e. upright) type. Its requirements are expressed i
15、n sentences in which the principal auxiliary verb is “shall”.Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary pr
16、ovisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.iv BSI 2007 This page deliberately left blankBS 939:2007 BSI 2007 1BS 939:2007Section 1: General1 ScopeThis British Standard specifies requiremen
17、ts for engineers try squares (excluding adjustable squares), cylindrical squares and block squares of solid or open form.Section 1 specifies general requirements applicable to all types of square.Section 2 specifies requirements for engineers try squares in three grades of accuracy, AA, A and B, wit
18、h inner lengths of blade from 50 mm up to and including 1 000 mm.Section 3 specifies requirements for cylindrical squares in accuracy grade AA in sizes from 75 mm up to and including 750 mm.Section 4 specifies requirements for solid form block squares in accuracy grades AA and A in sizes from 50 mm
19、40 mm up to and including 1 000 mm 1 000 mm.Section 5 specifies requirements for open form block squares in accuracy grades A and B in sizes from 150 mm 100 mm up to and including 600 mm 400 mm.NOTE While the standard provides for squares in various grades of accuracy, it should be noted that their
20、accuracy in use is dependent upon the flatness of the surfaces on which they are used.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of t
21、he referenced document (including any amendments) applies.BS 1134-1, Assessment of surface texture Part 1: Methods and instrumentationBS EN 1561:1997, Founding Grey cast ironsBS 3643-1:1981, ISO metric screw threads Principles and basic dataBS 3643-2:1981, ISO metric screw threads Specification for
22、selected limits of size3 Terms and definitionsFor the purposes of this British Standard the nomenclature given in Figure 2a), Figure 6, Figure 7 and Figure 8, and the following terms and definitions apply.3.1 deviation from straightness and flatnessminimum distance between two parallel planes that j
23、ust enclose the surface under considerationBS 939:20072 BSI 20073.2 deviation from parallelismdifference between the maximum and minimum distances separating the surfaces or edges under consideration3.3 Squareness of two surfaces3.3.1 deviation from squarenessminimum distance between two parallel pl
24、anes that will just enclose one surface (A), including any straightness error of surface (A), and that are perpendicular to a datum plane in contact with the other surface (B) (see Figure 1)3.3.2 squareness tolerancemaximum permissible deviation from squareness (see Figure 1)3.4 tolerancesmaximum pe
25、rmissible deviations from straightness, flatness, parallelism and squareness4 Protection against climatic conditionsAll surfaces of the squares shall be protected against climatic conditions by being covered with a suitable corrosion preventative preparation or a paper impregnated with a vapour phas
26、e inhibitor (VPI).NOTE 1 Temporary (easily removable) corrosion preventatives are dealt with fully in BS 1133-6.2.NOTE 2 Guidance on sealed packs with desiccants is given in BS 1133-19.Figure 1 Exaggerated illustration of deviation from squareness and squareness toleranceKey1 Squareness tolerance2 D
27、eviation from squareness3 Surface A (long side)4 Datum plane5 Surface B (short side)1902345 BSI 2007 3BS 939:2007Section 2: Engineers try squares5 Designating sizeThe designating size of an engineers try square shall be the length of the blade from its tip to the inner working face of the stock (see
28、 Figure 2).6 Recommended sizesRecommended sizes (in mm) of engineers try squares are: 50, 75, 100, 150, 200, 300, 450, 600, 800 and 1 000; squares of other sizes shall be ordered only when it is not practicable to adopt one of the recommended sizes. If squares of intermediate sizes are supplied they
29、 shall be made to the same tolerances as those specified for the next smaller recommended size.Figure 2 Engineers try squaresKey1 Thickness of blade2Side face of blade3Side face of stock4 Thickness of stock5Width6Blade7 Outer edge of blade8 Inner edge of blade9Relief10 Inner working face of stock11
30、Inner length of blade and designating size of square12 Depth13 Stock14 Outer working face of stockKey1Reliefa) Nomenclature b) Other forms of relief1234567981013 1412110.5 max11BS 939:20074 BSI 20077 Material and manufactureAll engineers try squares shall be made of good quality steel. The working s
31、urfaces of grades AA and A squares shall be hardened to a value of not less than 600 HV and subjected to an appropriate stabilization process.8 General features of design8.1 When the blade and stock of a try square are built up from separate parts, the blade shall be rigidly and permanently fixed in
32、 the stock.Grade AA try squares shall have the inner and outer edges of the blade bevelled so that the approximate width of the reduced edge is as follows (see also Annex A):8.2 For all three grades of try square the stock shall be relieved at the junction of the inner edge of the blade and the inne
33、r working face of the stock see Figure 2a).The inner working face of the stock may be terminated at its junction with the inner edge of the blade, in which case the area of the working face of the stock, which projects along both sides of the blade, shall be relieved below the plane of the working f
34、ace of the stock see Figure 2b).NOTE The blade may be recessed from the outer working face of the stock by not more than 0.5 mm see Figure 2b).9 Finish All working surfaces of the blade and stock of the three grades of engineers try square shall have a lapped, finely ground or polished finish, havin
35、g a surface roughness value of 1.0 4m Ramaximum according to BS 1134-1, and all sharp edges shall be removed.Size of square Approximate width of bevelled edgemm mm50 and 75 0.25100 and 150 0.40200 and 300 0.65450 0.75600 1.00800 and 1 000 1.50 BSI 2007 5BS 939:200710 Accuracy10.1 Straightness of inn
36、er and outer edges of bladeEach edge of the blade shall be straight to within the tolerance specified in Table 1 when the outer working face or side face of the stock is resting on a horizontal surface.10.2 Parallelism of blade edgesThe blade edges shall be parallel to each other to within the toler
37、ances specified in Table 2.Table 1 Tolerances on straightness of blade edgesSize of square ToleranceGrade AA Grade A Grade Bmm 4m 4m 4m50, 75 2 4 8100, 150 2 4 8200 2 4 8300 3 6 12450 4 8 16600 6 12 24800 8 16 321 000 10 20 40Table 2 Tolerances on parallelism of blade edgesSize of square ToleranceGr
38、ade AA Grade A Grade Bmm 4m 4m 4mUp to 150 3 5 8200, 300 3 8 12450, 600 7 12 18800, 1 000 12 18 24BS 939:20076 BSI 200710.3 Flatness of working faces of stockEach working face of the stock shall be flat to within the tolerance specified in Table 3. Deviations from flatness shall be of concave nature
39、 to prevent rock.10.4 Parallelism of working faces of stockThe working faces of the stock shall be parallel to within the tolerances specified in Table 4.10.5 Parallelism of side faces of stockThe side faces of the stock shall be parallel to within the tolerance specified in Table 5.Table 3 Toleranc
40、es on flatness of working faces of stockSize of square ToleranceGrade AA Grade A Grade Bmm 4m 4m 4m50, 75 1 2 4100, 150 1.5 3 6200 2 4 8300 2 4 8450 2.5 5 10600 4 8 16800 5 10 201 000 6 12 24Table 4 Tolerances on parallelism of working faces of stockSize of square ToleranceGrade AA Grade A Grade Bmm
41、 4m 4m 4mUp to 150 2 3.5 5200, 300 3 5 8450, 600 5 8 12800, 1 000 8 12 16Table 5 Tolerances on parallelism of side faces of stockSize of square ToleranceAll gradesmm 4mUp to 150 25200, 300 50450, 600 100800, 1 000 150 BSI 2007 7BS 939:200710.6 Squareness of side faces of stock to working faces of st
42、ockThe side faces of the stock shall be square to the working faces as follows: Grade AA to within 1 m/mm Grade A to within 2 m/mm Grade B to within 3 m/mm10.7 Squareness of edges of blade to side faces of stockThe inner and outer edges of the blade shall be square to the side faces of the stock to
43、within 15 m over the thickness of the edges. 10.8 Squareness of edges of blade to working faces of stockWhen the square is placed upright on a horizontal surface the maximum departure from squareness of:a) the outer edge of the blade to the outer working face of the stock; andb) the inner edge of th
44、e blade to the inner working face of the stock; shall not exceed the tolerance specified in Table 6 (see Figure 3).Table 6 Tolerances on squareness of blade edges to working faces of stockSize of square Tolerance measured at tip of bladeGrade AA Grade A Grade Bmm 4m 4m 4m50, 75 4 8 16100, 150 4 8 16
45、200 4 8 16300 6 12 24450 8 16 32600 12 24 48800 16 32 641 000 20 40 80BS 939:20078 BSI 200710.9 Lateral squareness of bladeThe blade shall be laterally square to the base of the stock to within the tolerances specified in Table 7 (see Figure 4).Figure 3 Squareness of blade edges to working faces of
46、stockKey1Eror2Se 10.8b)3Se 10.8a)123Table 7 Tolerance on lateral squareness of blade to base of stockSize of square Tolerance measured at tip of bladeGrade AA Grade A Grade Bmm 4m 4m 4m50, 75 50 75 125100, 150 75 125 250200, 300 125 200 375450 200 300 500600 250 300 500800 300 375 6001 000 300 375 6
47、50Figure 4 Lateral squareness of bladeKey1 Error190 BSI 2007 9BS 939:200711 RigidityWhen the stock of the try square is rigidly clamped and a force of 3 N is applied to the free end of the blade in a horizontal direction parallel to the length of the stock, the end of the blade shall not deflect in
48、this direction by an amount greater than the tolerance specified in Table 6 (see Figure 5).NOTE This test is independent of any errors in the try square in its “free” condition.12 MarkingEach try square shall have legibly and permanently marked upon it the following:a) the number of this British Sta
49、ndard, i.e. BS 939;b) the grade designation, e.g. A;c) an identification number for grade AA try squares; andd) the manufacturers name or trade mark.Figure 5 RigidityKey1 Deflection under load23 N force3Stock rigidly held 123BS 939:200710 BSI 2007Section 3: Cylindrical squares13 Designating sizeThe designating size of a cylindrical square shall its length (see Figure 6).14 Recom
