BS 817-2008 Specification for surface plates《划线台规范》.pdf

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1、Specification for surface platesBS 817:2008BS 817:2008 BritiSh StandardPublishing and copyright informationthe BSi copyright notice displayed in this document indicates when the document was last issued. BSi 2008iSBn 978 0 580 62030 0iCS 17.040.30the following BSi references relate to the work on th

2、is standard: Committee reference tdW/4 draft for comment 08/30177873 dCPublication historyFirst published november 1938 Second edition June 1957 third edition March 1972 Fourth edition March 1983 Fifth edition december 1988 Sixth edition november 2008Amendments issued since publicationAmd. No. Date

3、Text affected BritiSh Standard BSI 2008 iBS 817:2008Summary of pagesthis document comprises a front cover, an inside front cover, pages i to ii, pages 1 to 16, an inside back cover and a back cover.ContentsForeword ii1 Scope 12 normative references 13 terms and definitions 14 information to be suppl

4、ied and items to be agreed 25 Classification 26 Materials 37 Construction 58 Finish 69 rigidity of surface plates of 400 mm 250 mm or 12 in 12 in, and larger 710 accuracy 711 Cover and other protection 912 Marking 9Annexesannex a (informative) recommendations on the care and use of surface plates 10

5、annex B (normative) test for rigidity of surface plates 11annex C (informative) assessment of bearing area of cast iron surface plates 13annex d (informative) Calculation of permitted deviation from flatness of the working surface 14Bibliography 15List of figuresFigure 1 Components of a surface plat

6、e 3Figure 2 Variation gauge 4Figure B.1 Cast iron surface plate being subjected to rigidity test 12Figure B.2 Endon view of rigidity test apparatus 12List of tablestable 1 Permitted deviations from flatness of the working surface 8table 2 Permitted variations of the working surface 9BS 817:2008ii BS

7、I 2008BritiSh StandardForewordPublishing informationthis British Standard is published by BSi and came into effect on 30 november 2008. it was prepared by technical Committee tdW/4, Technical product realization. a list of organizations represented on this committee can be obtained on request to its

8、 secretary.Supersessionthis British Standard supersedes BS 817:1988, which is withdrawn.Information about this documentthis British Standard has been revised to bring it up to date.the tolerances are given in metric units, including those for the inch sizes of surface plate, and the intended use of

9、plates of each of the four grades of accuracy specified is included for information. Presentational conventionsthe provisions of this standard are presented in roman (i.e. upright) type. its requirements are expressed in sentences in which the principal auxiliary verb is “shall”.Commentary, explanat

10、ion 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 provisions of a contract. Users are responsible for its correct application.Complia

11、nce with a British Standard cannot confer immunity from legal obligations.BritiSh Standard BSI 2008 1BS 817:20081 Scopethis British Standard specifies the construction, and dimensions and tolerances, for rectangular and square surface plates for use as working planes for engineering purposes, made o

12、f cast iron or granite, in two size ranges, from 160 mm 100 mm to 2 500 mm 1 600 mm and from 12 in 12 in to 96 in 48 in, and in four grades of accuracy.the standard is applicable to new surface plates and to plates that are being resurfaced after they have become worn.in addition to the definitive r

13、equirements, this standard also requires the items detailed in Clause 4 to be documented. For compliance with this standard, both the definitive requirements and the documented items have to be met.NOTE 1 The inch sizes are given as this information is still required by industry. Attention is drawn

14、to the fact that metric dimensions are not necessarily direct conversions of the imperial dimensions.NOTE 2 General information on the care and use of surface plates is given in Annex A.2 Normative referencesthe following referenced documents are indispensable for the application of this document. F

15、or dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.BS 113319, Packaging code Section 19: Use of desiccants in packagingBS En 1561:1997, Founding Grey cast irons3 Terms and definitionsFor the pu

16、rposes of this British Standard the following terms and definitions apply.NOTE The components of a surface plate are illustrated in Figure 1, which also gives the nomenclature.3.1 surface plateiron casting or block of granite with a worked surface which is used as a working plane and a datumNOTE Sur

17、face plates of larger sizes which are mounted on a stand are usually known as “surface tables” but for simplicity the term “surface plate” is used throughout this standard.3.2 deviation from flatness of the working surfaceminimum distance separating the parallel planes between which the whole of the

18、 working surface can just be containedBS 817:20082 BSI 2008BritiSh Standard3.3 variation of the working surfacevariation in the indicator reading when the working surface is explored with the variation gauge NOTE See 3.4 and Figure 2.3.4 variation gaugefreely moving base with three coplanar pads for

19、 bearing on the surface being tested, and carrying an indicator measuring variations of that surface through a fourth padNOTE This is as shown in Figure 2.4 Information to be supplied and items to be agreed4.1 Information to be supplied by the purchaserthe following information to be supplied by the

20、 purchaser shall be fully documented. For compliance with the standard both the definitive requirements specified throughout the standard and the following documented items shall be satisfied:the size of the plate, if other than one of the nominal sizes a) specified in table 1 (see 7.1);if a particu

21、lar working height is required (see note to b) 7.4);if projections are required on cast iron surface plates smaller than c) 400 mm 250 mm or 12 in 12 in or on granite surface plates (see 7.5);if handles are required on the surface plate (see d) 7.7).4.2 Items to be agreed between the contracting par

22、tiesthe following items to be agreed between the contracting parties are specified in the clauses referred to and shall be fully documented. For compliance with the standard both the definitive requirements specified throughout the standard and the following documented items shall be satisfied:the n

23、umber of primary supporting feet, and the manner of setting, a) if more than three primary supporting feet are required (see 7.3);NOTE Large plates for special purposes might need to be supported on more than three primary feet.the tolerances on the lengths of the sides if the purchaser b) requires

24、the sides to be finished straight, parallel and mutually square (see 7.6).5 ClassificationSurface plates shall be classified as Grade 0, 1, 2 or 3 according to their accuracy as specified in Clause 10.NOTE Grade 0 is necessary for measurements to a high accuracy. Grade 1 is intended for general insp

25、ection purposes. Grade 2 is intended for BritiSh Standard BSI 2008 3BS 817:2008marking out purposes. Grade 3 is suitable for lower grade marking out or as a general support plate.6 Materials6.1 Cast iron plates6.1.1 GeneralClosegrained cast iron not inferior to material designation EnGJL100 (number:

26、 EnJL1020) in BS En 1561:1997, table 1, shall be used. the castings, when inspected visually, shall be free from blowholes or porous patches that might affect stability or accuracy. NOTE The plugging of blowholes or porous patches in the working surface with material of a similar composition is perm

27、itted provided that such a repair does not affect stability or accuracy.Figure 1 Components of a surface platea) typical cast iron surface plate321645TKey Framing and ribbing1 Side2 Working surface3 total depth 4 Projection 5 Supporting feet6 b) typical granite surface plate3214Key Side1 Working sur

28、face2 total depth3 Supporting feet4 BS 817:20084 BSI 2008BritiSh Standard6.1.2 Stress reliefafter being cast and rough machined, Grades 0 and 1 surface plates shall be subjected to a stress relief process before being finished.NOTE Details of the stess relief process to which the plates have been su

29、bjected should be made available to the purchaser on request.6.2 Granite platesthe granite shall be closegrained and of uniform texture, sound, and free from flaws and fissures and from inclusions of softer materials. NOTE Repair of defects in the working surface is not permitted.Figure 2 Variation

30、gauge124337.5100 10037.5dimensions in millimetrestypical detail of floating pad1 200-1KeyWorking surface1 NOTE Tolerance is 1 mm, except where otherwise state.KeySensitive indicator 1 (minimum magnification 2 500)handle2 Fixed pads 203 100, flat and coplanar to 1 m 204 100floating indicator pad, fre

31、e to follow working surfaceBritiSh Standard BSI 2008 5BS 817:20087 Construction7.1 Size of plateUnless otherwise specified by the purchaser see 4.1a), the plate shall be of one of the nominal sizes specified in table 1.7.2 Border zoneif the working surface is surrounded by a border zone, the width o

32、f the border zone shall not exceed the value specified in table 1. For sizes of plates not specified in table 1 see 4.1a) the width of the border zone shall not exceed 2% of the length of the shorter side of the plate, or 10 mm, whichever is the smaller.7.3 Supporting feet Unless otherwise agreed be

33、tween the contracting parties see 4.2a), surface plates shall be provided with three primary supporting feet; one at the centre of one short side and one at each end of the other short side. to limit tipping, two safety feet shall be provided at the single foot end of surface plates (toward the ends

34、 of the short side) of 400 mm 250 mm or 18 in 12 in and larger.Supporting feet shall be machined.7.4 Standthe surface plate shall be supplied with a stand which shall be constructed and braced in such a way that it rigidly supports the surface plate. the support surfaces on the stand shall be machin

35、ed and means of leveling the surface plate shall be provided together with means of resisting accidental displacement of the surface plate from the stand.NOTE Unless a particular working height is specified by the purchaser see 4.1b), the overall height of a surface plate on its stand, i.e. the heig

36、ht of the working surface above the floor, should be approximately 850 mm.7.5 Projection of topProjections shall be provided on cast iron surface plates of 400 mm 250 mm or 12 in 12 in and larger.if specified by the purchaser, projections shall be provided on cast iron surface plates smaller than 40

37、0 mm 250 mm or 12 in 12 in and on granite surface plates see 4.1c).NOTE The provision of projections on cast iron surface plates smaller than these sizes or on granite surface plates is optional.Where provided, projections shall be at least 25 mm for surface plates of 400 mm 250 mm or 12 in 12 in an

38、d larger and at least 20 mm for surface plates smaller than these sizes. the undersides of projections shall be finished such that they can accommodate clamps.BS 817:20086 BSI 2008BritiSh Standard7.6 Sides and edgesthe four sides of the surface plate shall be machined and, unless otherwise agreed be

39、tween the contracting parties see 4.2b), the lengths of the sides shall each be within 2% of the nominal size specified in table 1 and the edges shall be rounded.7.7 Handlesif specified by the purchaser, cast iron surface plates shall be provided with handles see 4.1d).Granite surface plates shall n

40、ot be provided with handles.7.8 Tapped holes or insertsWhere tapped holes or inserts are required the necessary work shall be carried out before the working surface is finished (see note 1). the holes or inserts shall be counterbored.NOTE 1 Tapped holes or inserts are only provided if requested by t

41、he purchaser.NOTE 2 The preferred size thread is M6, but smaller sizes are acceptable (see BS 36431).NOTE 3 The use, for clamping purposes, of tapped holes in cast iron surface plates or tapped inserts in granite surface plates can give rise to distortion of the working surface if high clamping pres

42、sures are applied. Metal inserts in granite surface plates can cause distortion due to differential expansion.8 Finish8.1 Cast iron surface platesthe working surface of Grades 0 and 1 surface plates shall be finished either by scraping or by another process that results in a surface such as that obt

43、ained by scraping. the working surface of Grades 2 and 3 surface plates shall be finished either by one of the same processes or by machining.the proportion of bearing area shall be not less than 20% for Grades 0 and 1 surface plates, and not less than 10% for Grades 2 and 3 surface plates (see note

44、). high spots on scraped surfaces shall be uniformly distributed and the percentage of bearing area shall not be so high as to cause wringing.Unmachined surfaces of cast iron surface plates shall be finished by painting.NOTE A suitable method of test for assessing the bearing area is given in Annex

45、C. Other proven methods may also be used.BritiSh Standard BSI 2008 7BS 817:20088.2 Granite surface platesthe working surface of Grades 0 and 1 surface plates shall be finished by lapping. the working surface of Grades 2 and 3 surface plates shall be finished by lapping or left as ground.8.3 Finished

46、 working surfacethe finished working surface of new surface plates shall be free from any defects that might affect their stability or accuracy.9 Rigidity of surface plates of 400 mm 250 mm or 12 in 12 in, and largerWhen the surface plate is tested in accordance with annex B, the deflection of the l

47、oaded area shall be not more than 1 m/200 n.10 Accuracy10.1 Working surfacethe working surface, excluding a border zone, shall conform to 10.2 and 10.3.the width of the border zone shall not exceed 2% of the length of the shorter side, or 10 mm, whichever is the smaller, and no point on the border s

48、hall project above the working surface.10.2 Deviation from flatness of the working surfacethe flatness of the working surface shall not exceed the permitted deviations specified in table 1.BS 817:20088 BSI 2008BritiSh Standardtable 1 Permitted deviations from flatness of the working surfaceMetric si

49、zesNominal size of plateA)Permitted border zone Permitted deviations from flatnessGrade 0 Grade 1 Grade 2 Grade 3mm 160 100 250 160 400 250 630 400 1 000 630 1 600 1 000B)2 000 1 000B)2 500 1 600B)mm 2 3 5 8 10 10 10 10 m 3.0 3.5 4.0 4.5 5.5 7.5 8.5 10.0 m 6 7 8 9 11 15 17 20 m 12 14 16 18 22 30 34 40 m2428323644606880250 250 400 400 630 630 1 000 1 000B)5 8 10 10 3.5 4.0 5.0 6.5 7 8 10 13 14 16 20 26 28324052Inch sizesNominal size of plate Permi