Geometric Dimensioning and Tolerancing Unit 1 Introduction Symbols

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

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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. EML 2023 Computer Aided Design

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 EML 2023 Computer Aided Design

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. EML 2023 Computer Aided Design 5

Tolerance Notes EML 2023 Computer Aided Design 6

Limit Tolerancing EML 2023 Computer Aided Design

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 perfect location for hole center +. 005 EML 2023 Computer Aided Design

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. EML 2023 Computer Aided Design

History of Dimensioning and Tolerancing Standards in the USA Mil Std 8 1950’s Mil Std 8 A Mil Std 8 B Mil Std 8 C-1963 ASA-Y 14. 5 -1957 USASI Y 14. 5 -1966 ANSI Y 14. 5 -1973 ANSI Y 14. 5 M-1982 ASME Y 14. 5 M-1994 ASME Y 14. 5 -2009 1. 3 EML 2023 Computer Aided Design

Introduction • GDT is a language of symbols • We will see an overview of the symbols associated with: 1. Dimensioning Symbols 2. Geometric Characteristics 3. Modifying Symbols EML 2023 Computer Aided Design 12

Dimensioning Symbols EML 2023 Computer Aided Design 13

Dimensioning Symbols Diameter Radius R EML 2023 Computer Aided Design 14

Dimensioning Symbols Spherical Diameter S Spherical Radius SR EML 2023 Computer Aided Design 15

Dimensioning Symbols Controlled Radius Tolerance CR Number of Places A controlled radius has no ‘reversals’, but is a smooth curve within the tolerance zone. EML 2023 Computer Aided Design 16

Dimensioning Symbols Counterbore/Spotface Countersink EML 2023 Computer Aided Design 17

Dimensioning Symbols Depth/Deep Dimensions Not to Scale EML 2023 Computer Aided Design 18

Dimensioning Symbols Conical taper Slope EML 2023 Computer Aided Design 19

Dimensioning Symbols Square Reference Dimension EML 2023 Computer Aided Design 20

Dimensioning Symbols Dimension Origin Arc Length EML 2023 Computer Aided Design 21

Dimensioning Symbols All Around All Over EML 2023 Computer Aided Design 22

Dimensioning Symbols Chain Line Used to identify a limited region to be treated differently from the rest of the part. EML 2023 Computer Aided Design 23

Introduction • We will see an overview of the symbols associated with: 1. Dimensioning Symbols 2. Geometric Characteristics 3. Modifying Symbols EML 2023 Computer Aided Design 24

Geometric Characteristics Explained in detail in Chapters 6 and 8. EML 2023 Computer Aided Design 25

Introduction • We will see an overview of the symbols associated with: 1. Dimensioning Symbols 2. Geometric Characteristics 3. Modifying Symbols EML 2023 Computer Aided Design 26

Modifying Symbols EML 2023 Computer Aided Design 27

Modifying Symbols Maximum Material Condition MMC Refers to the size of the feature associated with the most material. EML 2023 Computer Aided Design 28

Modifying Symbols Least Material Condition LMC Refers to the size of the feature associated with the least material. EML 2023 Computer Aided Design 29

Modifying Symbols Continuous Feature Basic Dimension Used to describe a theoretically exact size. EML 2023 Computer Aided Design 30

Modifying Symbols Between EML 2023 Computer Aided Design 31

Geometric Dimensioning and Tolerancing (GDT) 1. establish a reference coordinate system by defining datums 2. provide basic dimensions (perfect dimensions) relative to the datums 3. specify allowable tolerances EML 2023 Computer Aided Design