TAILIEUCHUNG - Machinery's Handbook 27th Episode 1 Part 9

Tham khảo tài liệu 'machinery's handbook 27th episode 1 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 635 Machinery s Handbook 27th Edition GEOMETRIC DIMENSIONING Ị Datum letter Leader may be appropriately directed to a feature. Ị-ệ-Ị M I A I B I C È Datum triangle may be filled or not filled. Combined feature control frame and datum identifier Fig. 1. Datum Feature Symbol Datum Plane The individual theoretical planes of the reference frame derived from a specified datum feature. A datum is the origin from which the location or other geometric characteristics of features of a part are established. Datum Reference Frame Sufficient features on a part are chosen to position the part in relationship to three planes. The three planes are mutually perpendicular and together called the datum reference frame. The planes follow an order of precedence and allow the part to be immobilized. This immobilization in turn creates measurable relationships among features. Datum Simulator Formed by the datum feature contacting a precision surface such as a surface plate gage surface or by a mandrel contacting the datum. Thus the plane formed by contact restricts motion and constitutes the specific reference surface from which measurements are taken and dimensions verified. The datum simulator is the practical embodiment of the datum feature during manufacturing and quality assurance. Datum Target A specified point line or area on a part used to establish a datum. Degrees of Freedom The six directions of movement or translation are called degrees of freedom in a three-dimensional environment. They are up-down left-right fore-aft roll pitch and yaw. Fig. 2. Degrees of Freedom Movement That Must be Controlled Depending on the Design Requirements. Copyright 2004 Industrial Press Inc. New York NY 636 Machinery s Handbook 27th Edition GEOMETRIC DIMENSIONING Dimension Basic A numerical value used to describe the theoretically exact size orientation location or optionally profile of a feature or datum or datum target. Basic dimensions are indicated by a rectangle around the dimension .

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