ALL CONCEPTS IN GEOMETRIC DIMENSIONING AND TOLERANCING (GD & T)

Posted on 28 Apr 2020 07:18 pm

GEOMETRIC DIMENSIONING AND TOLERANCING :- Defined Geometric dimensioning and tolerancing is a dimensioning practice which allows designers to set tolerance limits not just for the size of an object, but for all of the various critical characteristics of a part. In applying geometric dimensioning and tolerancing to a part, the designer must examine it in terms of its function and its relationship to mating parts . It is taken from the dimensioning standards as defined by the American National Standards Institute (ANSI), written by the American Society of Mechanical Engineers (ASME) or ASME Y14.5M–1994. This manual is a necessary referance for drafters and designers involved in geometric dimensioning and positional tolerancing. Another concept that must be understood in order to effectively apply geometric tolerancing is the concept of datums. For skilled, experienced designers, the geometric building blocks, modifiers, and datums blend together as a single concept. However, for the purpose of learning, they are dealt with separately, and undertaken step-by-step as individual concepts. They are presented now in the following order: modifiers, datums, and geometric building blocks . C H A P T E R O B J E C T I V E S :- Upon completion of this chapter students should be able to do the following: - Describe what is meant by the term general toleancing . - D e fine the concept geometric dimensioning and toleancing . - Explain the purpose of a modifier. -Distinguish between the concepts maximum material condition (MMC) and regardless of feature size (RFS). -Explain the concept least material condition (LMC). - Describe what is meant by projected tolerance zone. - Make a sketch that illustrates the concept of datums. -Demonstrate how to establish datums. -Apply feature control symbols when dimensioning objects . -Explain the concept of True position. KEY TERMS :- -All around symbol -Angularity -Basic dimension -Between symbol -Bilateral tolerance -Circularity -Cylindricity -Datum -Datum feature -Datum feature simulator -Datum feature symbol -Datum plane -Datum reference frame -Datum surface -Datum target symbol -Feature control symbol -Flatness -Free-state variation -Geometric dimensioning and tolerancing -General tolerancing -Least material condition (LMC) -Limit dimensioning -Maximum material condition (MMC) -Modifiers -Parallelism -Perpendicularity -Positional tolerancing -Profile -Profile of a line -Profile of a surface -Projected tolerance zone -Regardless of feature size (RFS) -Runout -Size tolerance -Statistical tolerancing symbol -Straightness -Tangent plane -True position -Unilateral tolerance -Virtual condition REFERENCE :- 1)UNITREAD DESIGN TEAM 2)ASME Y14.5-2018