Unformatted text preview: Geometric Tolerancing 1 Geometric Tolerancing Referred to as GD&T Geometric Dimensioning & Tolerancing Follows ANSI Y14.5M, 1982 standard Developed from 1973 standard which was a modification of MIL-STD-8 (1940's) 2 Geometric Tolerancing Why change from +/- tolerancing to GD&T? Lack of specified datums Lack of maximum material concept Non-uniform interpretation Poor method to locate basic features (holes) Ex: 3 Holes Located using +/- 4 Creation of a Square Tolerance Zone 5 More Tolerance Diagonally than Flats 6 Plus/Minus Tolerancing Not logical Do not want holes to be off location more in one direction than another Hole location tolerance should be the same in any direction Manufacturing does not use the tolerance, they place the holes exactly as the dimension dictate Inspection process determines actual location
7 Advantages of GD&T Locating holes should be like shooting at a bullseye Aim for the exact center & then check afterward Are we off center? Tolerance zone should be round, not square Round tolerance zones measure the same in any direction
8 Round Tolerance Zone 9 Advantages of GD&T Round tolerance zones actually give us additional tolerance over square zones 10 Advantages of GD&T Round tolerance zones actually give us additional tolerance over square zones 11 How GD&T Works Need round tolerance zone Dimensions must be exact or basic Dimensions will have no tolerance 12 How GD&T Works Cannot build anything "perfect" with no tolerance Must have tolerance somewhere Place tolerance in a frame under the holes Basic dimension...
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- Spring '08
- Datum reference, Geometric Characteristic Symbols