Understanding Geometric Dimensioning and Tolerancing in Engineering, Study Guides, Projects, Research of English Literature

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Dimensioning and

Tolerancing

Dimensioning

 Before an object can be built, complete information about both the size and shape of the object must be available. The exact shape of an object is communicated through orthographic drawings, which are developed following standard drawing practices. The process of adding size information to a drawing is known as dimensioning the drawing.

Dimensioning

 If a part is dimensioned properly, then

the intent of the designer is clear to

both the person making the part and

the inspector checking the part.

 A fully defined part has three

elements: graphics, dimensions, and

words (notes).

Size and Location

Dimensions

 A well dimensioned part will communicate the size and location requirements for each feature. Communications is the fundamental purpose of dimensions.

 Parts are dimensioned based on two criteria:  Basic size and locations of the features.  Details of a part's construction and for manufacturing.

Unit of measure

 Occasionally, a company will used

dual dimensioning, that is, both metric and English measurements on a drawing.

 Angular dimensions are shown either

in decimal degrees or in degrees, minutes, and seconds.

Terminology

 Leader line is the thin solid line used to indicate the feature with which a dimension, note, or symbol is associated.

 Tolerance is the amount a particular dimension is allowed to vary.

 Plus and minus dimensioning is the allowable positive and negative variance from the dimension specified.

Terminology

 Limits of size is the largest

acceptable size and the minimum acceptable size of a feature.

 The largest acceptable size is

expressed as the maximum material

condition (MMC)

 The smallest acceptable size is

expressed as the least material

condition (LMC).

Terminology

 Diameter symbol is the symbol which is placed preceding a numerical value indicating that the associated dimension shows the diameter of a circle. The symbol used is the Greek letter phi.

 Radius symbol is the symbol which is placed preceding a numerical value indicating that the associated dimension shows the radius of a circle. The radius symbol used is the capital letter R.

Terminology

 Datum is the theoretically exact point

used as a reference for tabular dimensioning.

Basic Concepts

 Dimensions are used to describe the

size and location of features on parts for manufacture. The basic criterion is, "What information is necessary to make the object?" Dimensions should not be excessive, either through duplication or dimensioning a feature more than one way.