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Dimensioning and Tolerancing Part 5

Tham khảo tài liệu 'dimensioning and tolerancing part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | DIMENSIONING AND TOLERANCING ASME Y14.5M-1994 a Datum features True geometric counterpart of datum feature B MMC virtual condition cylinder perpendicular to datum plane A Datum Plane A True geometric counterpart of datum feature A True geometric counterpart of datum feature c MMC virtual condition width perpendicular to datum plane A Center plane aligned with datum axis B b True geometric counterparts FIG. 4-9 d Datum reference frame DEVELOPMENT OF A DATUM REFERENCE FRAME FOR PART IN FIG. 4-8 determined. See para. 4.5.2. The effect of its material condition and order of precedence should be considered relative to lit and function of the part. Figure 4-18 a illustrates a part with a pattern of holes located in relation to diameter A and surface B. As indicated by asterisks datum requirements may be specified in three different ways. 4.5.6.1 Cylindrical Feature at RFS Primary. In Fig. 4-18 b diameter A is the primary datum feature and RFS is applied surface B is the secondary datum feature. The datum axis is the axis of the smallest circumscribed cylinder that contacts diameter A that is the actual mating envelope of diameter A. This cylinder encompasses variations in the size of A within specified limits. However any variation in perpendicularity between surface B and diameter A the primary datum feature will affect the degree of contact of surface B with its datum plane. 4.5.6.2 Surface Primary. In Fig. 4-18 c surface B is the primary datum feature diameter A is the secondary datum feature and RFS is applied. The datum axis is die axis of the smallest circumscribed cylinder that contacts diameter A and is perpendicular to the datum plane that is the actual mating envelope of a diameter that is perpendicular to datum plane B. In addition to size variations this cylinder encompasses any variation in perpendicularity between diameter A and surface B the primary datum feature. 4.5.6.3 Cylindrical Feature at MMC Secondary. In Fig. 4-18 d surface B is the primary datum .