GD&T
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Transcript of GD&T
GEOMETRIC DIMENSIONING AND TOLERANCING
WHAT IS GD & T ?
GD & T is symbolic language It is used to specify the size, shape, form,
orientation and location of features on a partIt is a design toolIt communicates design intent
ORIGIN OF GD & T
The world war two story
USASI Y14.5 – 1966
ANSI Y14.5 – 1973ANSI Y14.5 – 1982ASME Y14.5 – 1994ASME Y14.5 - 2009 (currently used)
WHEN TO USE GD & T
Drawing delineation and interpretation need to be the same
Features are critical to function or interchangeability
It is important to stop scrapping perfectly good parts
It is important to reduce drawing changes Automated equipment is used Functional gagging is required It is important to increase productivity Companies want across-the-board savings
WHERE TO USE GD&T
ENGINERINGDESIGNDRAFTINGMANUFACTURINGASSEMBLYQUALITY
DIMENSIONING STANDARDS
ISO - - millimeters (mm)US - - inches (inch)
SCALE FACTOR : 1 inch = 25 mm
GEOMETRIC DIMENSIONING
Dimension – numerical value indicated in a drawing to define size, shape, location and surface texture.
TYPES 1. Chain dimensioning 2. Datum dimensioning
Alternate dimensioning practices:1. Arrowless dimensioning2. Arrowless tabular dimensioning3. Chart dimensioning
CHAIN DIMENSIONINGDATUM DIMENSIONING
TYPES OF DIMENSIONING
ARROWLESS ARROWLESS TABULAR
ALTERNATE DIMENSIONING PRACTICES
GEOMETRIC TOLERANCING
Tolerance – The total amount that a specific dimension is permitted to vary.
Limits – largest and smallest numerical value possible for the feature within the tolerance specified.
Fits - A coupling of two parts creates a fit 3 types: 1. Clearance fit
2. Interference fit3. Transition fit
MMCLMC
SYMBOLS AND TERMS
GD & T symbols are divided into 5 types
1. Dimensioning symbols2. Datum feature and Datum target symbols3. Geometric characteristic symbols4. Material condition symbols5. Feature control frame
DIMENSIONING SYMBOLS
DATUM
A datum is theoretically exact points, lines, or planes .It is the true geometric counter part of the datum feature.
DATUM FEATURE & DATUM TARGET SYMBOLS
FEATURE CONTROL FRAME
GEOMETRIC CHARACTERISTIC SYMBOLS
INSTRUMENTS USED
DIAL GAUGE INDICATORPROFILE PROJECTORCOORDINATE MEASURING MACHINE
(CMM)VERNIER HIEGHT GAUGESLIPSVERNIER SCALE AND SCREW GAUGESSURFACE PLATEANGULAR PLATE…etc…,
FORM
PROFILE
ORIENTATION
RUNOUT
LOCATION
PROJECTED TOLERANCE ZONE
INTERNAL FEATURE EXTERNAL FEATURE
VIRTUAL CONDITION