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Geometric Dimensioning and Tolerancing

Geometric Dimensioning and Tolerancing. Unit 1 – Introduction, Symbols, and Terms. History and Background. Eli Whitney, is the inventor of the cotton gin and a pioneer in the use of mass production methods.

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Geometric Dimensioning and Tolerancing

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  1. Geometric Dimensioning and Tolerancing Unit 1 – Introduction, Symbols, and Terms

  2. History and Background Eli Whitney, is the inventor of the cotton gin and a pioneer in the use of mass production methods. Around 1798, he won a contract to supply muskets to the United States government. The firearms manufacture were based on the concept of interchangeable parts. He made a presentation to congress by building 10 guns and assembling and disassembling them claiming the same exact parts and mechanisms. Eli Whitney 1765 - 1825

  3. Limit Tolerancing

  4. Limit Tolerancing

  5. Limit Tolerancing • Is the .620-.630 hole horizontal position measured from a true vertical plane or from the as built face? • A .005” tolerance on the horizontal and vertical position of the hole means that the position could be off by as much as.007”. max allowed error for hole center .007 +.005 perfect location for hole center +.005

  6. Limit Tolerancing • Limit tolerances don’t have an origin or any orientation or location relative to datums. • The datums are usually implied. • The drawings are subject to different interpretations. • Plus/minus tolerancing works well for individual features of size (ex. diameter of a shaft), but does not control the relationship between individual features very well.

  7. Geometric Tolerancing Workbook Everyone should have a workbook to follow along. It contains necessary reference information along with class exercises. Page numbers in yellow on the slides match pages in the workbook.

  8. History of Dimensioning and Tolerancing Standards in the USA Mil Std 8 1950’s Mil Std 8A Mil Std 8B Mil Std 8C-1963 ASA-Y14.5-1957 USASI Y14.5-1966 ANSI Y14.5-1973 ANSI Y14.5M-1982 ASME Y14.5M-1994 ASME Y14.5-2009 1.3

  9. Common Symbols Lightning bolts show new symbols 1.7

  10. Geometric Characteristic Symbols 1.10

  11. Common Tolerance Zone Shapes 1.11

  12. Geometric Tolerance Categories “Happy Features” 1.12

  13. Features of Size and Features without Size 1.9

  14. Tolerances • All dimensions require a tolerance. • A tolerance should be as large as possible without interfering with the function of the part to minimize production costs. • Consider how your part will be checked to see if it meets the tolerances.

  15. Tolerance Notes

  16. Geometric Dimensioning and Tolerancing (GDT) • establish a reference coordinate system by defining datums • provide basic dimensions (perfect dimensions) relative to the datums • specify allowable tolerances

  17. Common Symbols applied to a Drawing units are mm 25 10 18 ±1° 1.8

  18. C A B

  19. Specify flatness. Document tolerances for the center hole.

  20. Document tolerances for the outer holes.

  21. Document tolerances for the square hole.

  22. Document tolerances for the three slots.

  23. Dimension the thickness.

  24. Indexer Assembly 1.17

  25. Indexer Plate 1.17

  26. Indexer Assembly ASME Y14.41 - 2003, Digital Product Definition Data Practices 1.19

  27. Workshop Exercise 1.1 12 1.23

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