Dimensioning and Tolerances Practices.pdf

Fall2005- ENGR 3200U 1

Dimensioning and Tolerances Practices


A typical Engineering drawingGraphics, Dimensions and words


Dimensioning

Circle of informationConcurrent Engineering Environment

Dimensioning criteria for Size and Location:1- Basic size and location2- Detail for construction and manufacturing

Graphics, Dimensions and words


Dual Dimensioned DrawingMillimeters and decimal inches


Angular UnitsDecimal degree or degree, minutes and seconds


Important Elements of a Dimensional Drawing


1) DimensionThe numerical value that defines the size, shape, location surface texture or geometric characteristics of a feature.


Text height and Standards for Dimensions


2) Basic dimension-Exact size, location, orientation or profile-Rectangular box-Feature control frame-Relative to a coordinate system-Datum establish coordinate system

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3) Reference dimension-Parentheses-Only information-It is not for fabrication-A calculated size-Older standards: REF

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4) Dimension Lines-Thin solid lines-Are broken for inserting of the dimension number

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5) Arrows-Symbol placed at the end of dimension, leader or cutting planes line-Uniform in size and style\-Usually about 3mm (1/8)-On-third as wide as they are long

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Arrowhead-Symbol placed at the end of dimension, leader or cutting planes line-Uniform in size and style\-Usually about 3mm (1/8)-On-third as wide as they are long

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6) Extension Line-Thin, solid line-Perpendicular to dimension line

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7) Visible Gap-1mm (1/16)

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8) Leader Line-Thin, solid line-Neither horizontal nor vertical-3 mm shoulder

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9) Limit of size-Largest and Minimum acceptable size-Largest acceptable size expressed as the MAXIMUM MATERIAL CONDITION (MMC)-Minimum acceptable size expressed as the LEAST MATERIAL CONDITION (LMC)

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10) Plus or minus dimensions-May or may not be equal

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11) Diameter Symbol-Greek letter Phi ()- Symbol precedes a numerical value

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12) Radius Symbol-capital letter R- Symbol precedes a numerical value

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13) Tolerance-The amount that a particular dimension is allowed to vary- For all dimensions except reference dimensions-Expressed throw limit dimensioning, plus or minus dimensioning or a general note-The difference between the maximum and the minimum limits

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Dimensioning and Tolerances Practices.pdf

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