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1、BRITISH STANDARD BS 817:1988 Specification for Surface plates BS 817:1988 This British Standard, having been prepared under the direction of the General Mechanical Engineering Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 March 1988 BSI 12-199
2、8 First published November 1938 First revision June 1957 Second revision March 1972 Third revision March 1983 Fourth revision The following BSI references relate to the work on this standard: Committee reference GME/8 Draft for comment 85/75050 DC ISBN 0 580 16135 8 Committees responsible for this B
3、ritish Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Committee (GME/-) to Technical Committee GME/8, upon which the following bodies were represented: City of Birmingham Polytechnic Department of Trade and Industry (National Engineeri
4、ng Laboratory) Department of Trade and Industry (National Measurement Accreditation Service) Department of Trade and Industry (National Physical Laboratory) Gauge and Tool Makers Association Institution of Production Engineers Ministry of Defence Amendments issued since publication Amd. No.Date of i
5、ssueComments BS 817:1988 BSI 12-1998i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Nomenclature and definitions1 3Classification1 4Materials2 5Stress relief of cast iron surface plates2 6Rigidity2 7General features3 8Finish3 9Accuracy3 10Cover and other protection5 11Ma
6、rking5 Appendix A The care and use of surface plates6 Appendix B Test for rigidity of surface plate6 Appendix C Assessment of bearing area of cast iron surface plates8 Appendix D Calculation of permitted deviation from flatness overall of the working surface9 Figure 1 Nomenclature1 Figure 2 Variatio
7、n gauge2 Figure 3 Cast iron surface plate being subjected to rigidity test7 Figure 4 End-on view of rigidity test apparatus8 Table 1 Permitted deviations from flatness overall of the working surface4 Table 2 Permitted variations of the working surface5 Publications referred toInside back cover BS 81
8、7:1988 ii BSI 12-1998 Foreword This revision of BS 817 has been prepared under the direction of the General Mechanical Engineering Standards Committee. It supersedes BS 817:1983 which is withdrawn. BS 817 relates to surface plates, which serve as a working plane for many engineering purposes. In thi
9、s revision the tolerances have been given throughout in metric units, including those for the inch sizes of surface plate, and the intended use of each of the four grades of accuracy has been included for information. Account has been taken of the decisions of the International Technical Committee I
10、SO/TC 3 for surface plates. The design of the variation gauge has been modified. The tolerances for variation of the working surface have been reduced and now apply to surface plates of 250 mm 250 mm and above. A British Standard does not purport to include all the necessary provisions of a contract
11、. 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, pages i and ii, pages 1 to 10, an inside back cover
12、 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. BS 817:1988 BSI 12-19981 1 Scope This British Standard specifies requirements for rectangular or square, cast iron
13、 or granite, surface plates ranging from 160 mm 100 mm to 2 500 mm 1 600 mm and from 12 in 12 in to 96 in 48 in in four grades of accuracy. It applies to new surface plates, to surface plates in use and to those which, after wear, have been resurfaced as appropriate to their grade and size. NOTE 1Th
14、e inch sizes are given as this information is still required by industry. NOTE 2General information on the care and use of surface plates is given in appendix A. NOTE 3The titles of the publications referred to in this standard are listed on the inside back cover. 2 Nomenclature and definitions For
15、the purposes of this British Standard the nomenclature shown in Figure 1 and the following definitions apply. 2.1 surface plate an iron casting or block of granite with a worked surface which is used as a working plane and a datum NOTESurface plates of larger sizes which are mounted on a stand are u
16、sually known as surface tables but for the purposes of simplicity in this standard the term “surface plate” has been used throughout. 2.2 deviation from flatness overall of the working surface the minimum distance separating the two parallel planes between which the working surface can just be conta
17、ined 2.3 variation of the working surface the variation in the indicator reading when the working surface is explored with the variation gauge shown in Figure 2 2.4 variation gauge a freely moving base with three co-planar pads for bearing on the surface being tested, and carrying an indicator measu
18、ring variations of that surface through a fourth pad, as shown in Figure 2 3 Classification Surface plates are classified as grade 0, 1, 2 or 3 according to their accuracy as specified in clause 9. NOTEGrade 0 is necessary for measurements to a high accuracy. Grade 1 is intended for general inspecti
19、on purposes. Grade 2 is intended for marking out purposes. Grade 3 is suitable for lower grade marking out or as a general support plate. Figure 1 Nomenclature BS 817:1988 2 BSI 12-1998 4 Materials 4.1 Cast iron Close-grained cast iron not inferior to grade 180 of BS 1452 shall be used. The castings
20、 shall be free from blowholes or porous patches. The plugging of minor defects in the working surface with material of a similar composition is permitted provided that such a repair does not affect stability or accuracy. 4.2 Granite The granite shall be close-grained and of uniform texture, sound, a
21、nd free from flaws and fissures and from inclusions of softer materials. Repair of defects in the working surface is not permitted. 5 Stress relief of cast iron surface plates After being cast and rough machined, grades 0 and 1 surface plates shall be treated to relieve internal stresses before bein
22、g finished. NOTEThe supplier should, upon request, furnish the purchaser with a statement of the stress-relieving process given. 6 Rigidity 6.1 Cast iron surface plates of grades 0 and 1 shall be made with adequate ribbing and of sufficient total depth, and granite surface plates of the same grades
23、shall be of sufficient total depth, to ensure compliance with 6.2. Figure 2 Variation gauge BS 817:1988 BSI 12-19983 6.2 When a load is applied at the central area of a surface plate of 400 mm 250 mm or 12 in 12 in, or larger, the loaded area shall not deflect below the remaining area of the surface
24、 plate by more than 1 m per 200 N. NOTEA simple method of test is given in appendix B. 7 General features 7.1 Supporting feet of surface plates (see Figure 1) Surface plates shall be provided with three primary supporting feet; safety feet to limit tipping shall be provided at the single foot end of
25、 surface plates of 400 mm 250 mm or 18 in 12 in and larger. NOTELarge plates for special purposes may be supported on more than three primary feet. The number of feet and the manner of setting should be as agreed between purchaser and supplier. Supporting feet shall be machined. 7.2 Stand The stand
26、shall be constructed and braced such that it will rigidly support the surface plate. Support surfaces shall be machined and means of levelling the surface plate shall be provided together with means of resisting accidental displacement of the surface plate from the stand. NOTEUnless a special workin
27、g height is needed the overall height of a surface plate on its stand, i.e. the height of the working surface above the floor, should be about 850 mm. 7.3 Projection of top Projections shall be provided on cast iron surface plates of 400 mm 250 mm or 12 in 12 in and larger. NOTEThe provision of proj
28、ections 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 and larger and at least 20 mm for surface plates smaller than these sizes. The underside of pr
29、ojections shall be finished such that they can accommodate clamps. 7.4 Sides and edges The four sides of the surface plate shall be machined and their lengths shall each be within 2 % of nominal size. Their edges shall be rounded. NOTEIf the purchaser requires the sides to be finished straight, para
30、llel and mutually square the tolerances should be agreed with the supplier. 7.5 Handles Granite surface plates shall not be provided with handles. NOTECast iron surface plates may be provided with handles. 7.6 Tapped holes or inserts Where tapped holes or inserts are required the necessary work shal
31、l be carried out before the working surface is finished (see note 1). The holes or inserts shall be counterbored. NOTE 1Tapped holes or inserts are only provided if requested by the purchaser. NOTE 2The preferred size thread is M6 but smaller sizes are acceptable (see BS 3643-1). NOTE 3The use, for
32、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 pressures are applied. Metal inserts in granite surface plates can cause distortion due to differential expansion. 8 Finish 8
33、.1 Cast iron surface plates The working surface of grades 0 and 1 surface plates shall be finished either by scraping or by other process that results in a surface such as that obtained by scraping. The working surface of grades 2 and 3 surface plates shall be finished either by one of the same proc
34、esses or by machining. The proportion of bearing area shall be not less than 20 % for grades 0 and 1, and not less than 10 % for grades 2 and 3 surface plates (see note). High spots on scraped surfaces shall be uniformly distributed and the percentage of bearing area shall not be so high as to cause
35、 wringing. Unmachined surfaces of cast iron surface plates shall be finished by painting. NOTEA suitable method of test for assessing the bearing area is given in appendix C. Other proven methods may also be used. 8.2 Granite surface plates The working surface of grades 0 and 1 surface plates shall
36、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 working surface The finished working surface of new surface plates shall be free from such defects as will adversely affect the use of the surface plate for the i
37、ntended purpose (see clause 3). 9 Accuracy 9.1 The working surface The working surface, which excludes a border zone, shall comply with the requirements of 9.2 and 9.3. 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 poin
38、t on the border shall project above the working surface. BS 817:1988 4 BSI 12-1998 9.2 Deviation from flatness overall of the working surface (see 2.2) The flatness overall of the working surface shall not exceed the permitted deviations given in Table 1. Table 1 Permitted deviations from flatness o
39、verall of the working surface Metric sizes Nominal size of platea Permitted border zonePermitted deviations from flatness overall Grade 0Grade 1Grade 2Grade 3 mmmmmmmm 160 10023.061224 250 16033.571428 400 25054.081632 630 40084.591836 1 000 630105.5112244 1 600 1 000b107.5153060 2 000 1 000b108.517
40、3468 2 500 1 600b1010.0204080 250 25053.571428 400 40084.081632 630 630105.0102040 1 000 1 000b106.5132652 Inch sizes Nominal size of platePermitted border zonePermitted deviations from flatness overall Grade 0Grade 1Grade 2Grade 3 inmmmmmm 18 1264.081632 24 1894.591836 36 24105.5112244 48 36b106.51
41、32652 60 36b107.0142856 72 36b108.0163264 72 48b108.0163264 96 48b109.5193876 12 1264.081632 18 1894.591836 24 24105.0102040 36 36106.0122448 a The nominal metric sizes given in column 1 Table 1 are preferred. It is recommended that other sizes are ordered only when it is not practicable to adopt on
42、e of these. The permitted deviations from flatness overall of unlisted sizes shall be calculated in accordance with the formula given in appendix D. b These surface plates are often provided with a stand having more than three support points. The permitted deviation applies after the supports have b
43、een adjusted and set as follows. The plate is to be levelled on the stand by adjustments under the three primary feet. Any remaining supports are then adjusted just into contact without disturbing the setting of the level. These plates should be checked regularly and the correct setting maintained.
44、BS 817:1988 BSI 12-19985 9.3 Variation of the working surface (see 2.3) The variation of the working surface of surface plates of 250 mm 250 mm and above shall not exceed the permitted variations given in Table 2. NOTE 1Smaller sizes have not been included as their permitted deviations from flatness
45、 overall do not allow significant variation. NOTE 2It is important to limit variations of the working surface as abrupt local changes in form could cause excessive variations in work measurements using different positions on the working surface. Table 2 Permitted variations of the working surface 10
46、 Cover and other protection Each grade 0 or 1 surface plate shall be supplied with a cover to protect the working surface and the edges of the surface plate. During storage and transit the finished surfaces of cast iron surface plates shall be protected against climatic conditions by being covered w
47、ith a corrosion-resistant preparation selected from BS 1133-6 and by using desiccants as described in BS 1133-19. 11 Marking Each surface plate shall be either legibly and permanently marked, or shall bear a designation plate attached to one side, with the following information in characters not les
48、s than 3 mm high: a) the manufacturers name or trade mark; b) the number of this standard, i.e. BS 817:19881); c) the grade of accuracy; d) the year of manufacture; e) an identification number. Example X and Co. BS 817 Grade 0 1988 No. 1234 GradePermitted variations, t1 m 03 16 212 324 1) Marking BS
49、 817:1988 on or in relation to a product represents a manufacturers declaration of conformity, i.e. a claim by or on behalf of the manufacturer that the product meets the requirements of the standard. The accuracy of the claim is therefore solely the responsibility of the person making the claim. Such a declaration is not to be confused with third party certification of conformity, which may also be desirable. BS 817:1988 6 BSI 12-1998 Appendix A The care and use of s
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