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CHAPTER 10

CHAPTER 10. Dimensioning and Tolerancing. Learning Objectives. Identify and use common dimensioning systems Explain and apply dimensioning standards based on ASME Y14.5 -2009 Apply proper specific notes for manufacturing features Place proper general notes and flag notes on a drawing

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CHAPTER 10

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  1. CHAPTER 10 Dimensioning and Tolerancing

  2. Learning Objectives • Identify and use common dimensioning systems • Explain and apply dimensioning standards based on ASME Y14.5-2009 • Apply proper specific notes for manufacturing features • Place proper general notes and flag notes on a drawing • Interpret and use correct tolerancing techniques

  3. Learning Objectives • Prepare completely dimensioned multiview drawings from engineering sketches and industrial drawings • Apply draft angles as needed to a drawing • Dimension CAD/CAM machine tool drawings • Prepare casting and forging drawings

  4. Learning Objectives • Provide surface finish symbols on drawings • Solve tolerance problems including limits and fits • Use an engineering problem as the basis for your layout techniques • Describe the purpose of ISO 9000 Quality Systems Standard and related standards

  5. Dimensions • Required on detail drawings • Provide shape and size description • Size dimensions • Location dimensions • Notes • Local notes (specific notes) • General notes

  6. Dimensions

  7. ASME Dimensioning Standards • ASME Y14.5, Dimensioning and Tolerancing • General note: DIMENSIONING AND TOLERANCING PER ASME Y14.5-2009 • Several other ASME documents with standards related to dimensioning and tolerancing

  8. Dimensioning Definitions • Actual size • Allowance • Basic dimension • Bilateral tolerance • Datum • Diameter • Feature • Feature of size • Geometric tolerance • Least material condition (LMC) • Limits of dimension

  9. Dimensioning Definitions • Maximum material condition (MMC) • Nominal size • Radius • Reference dimension • Stock size • Specified dimension • Tolerance • Unilateral tolerance

  10. Fundamental ASME Y14.5 Dimensioning Rules • Each dimension has a tolerance except reference, maximum, minimum, or stock • Dimensioning and tolerancing must be complete • Show each necessary dimension of an end product • Select and arrange dimensions to suit the function and mating relationship of a part

  11. Fundamental ASME Y14.5 Dimensioning Rules • Dimensions must not be subject to more than one interpretation • Do not specify the manufacturing processes unless necessary • Identify nonmandatory dimensions with an appropriate note • Arrange dimensions to provide required information and optimum readability • Show dimensions in true profile views and visible outlines

  12. Fundamental ASME Y14.5 Dimensioning Rules • Dimension diameter or thickness of materials manufactured to gage or code numbers • 90°angle is implied for centerlines and lines • 90°basic angle is implied for centerlines located by basic dimensions • A zero basic dimension applies where axes, center planes, or surfaces are shown one over the other with established geometric controls

  13. Fundamental ASME Y14.5 Dimensioning Rules • Unless otherwise specified, all: • Dimensions and tolerances are measured at 20°C (68°F) • Dimensions and tolerances apply in a free state condition except for nonrigid parts • Tolerances apply for the full depth, length, and width of the feature • Dimensions and tolerances apply on the drawing where specified

  14. Fundamental ASME Y14.5 Dimensioning Rules • Coordinate systems: • Right-handed (arranged clockwise) • Labeled axes and positive direction shown • 3-D model complies with ASME Y14.41, Digital Product Definition Data Practices

  15. Dimensioning Components

  16. Dimensioning Symbols

  17. Unidirectional Dimensioning • Numerals, figures, and notes lettered horizontally • Read from the bottom of the drawing sheet • Mechanical drafting for manufacturing

  18. Aligned Dimensioning • Numerals, figures, and notes aligned with the dimension lines • Horizontal dimensions read from the bottom • Vertical dimensions read from the right side • Architectural and structural drafting 0

  19. Rectangular Coordinate Dimensioning without Dimension Lines • Ordinate dimensioning • Dimension values aligned with extension lines • Dimension represents a measurement originating from datums or coordinates • Features such as holes sized using specific notes or a table • Popular for: • Precision sheet metal part drawings • Electronics drafting

  20. Rectangular Coordinate Dimensioning without Dimension Lines

  21. Tabular Dimensioning • Form of rectangular coordinate dimensioning without dimension lines • Features dimensioned in a table

  22. Chart Dimensioning • Used when a part or assembly has one or more dimensions that change depending on the specific application

  23. Millimeter Dimensions • Millimeters (mm) • Common International System of Units (SI) unit of measure • General note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS • Follow any inch dimensions with IN

  24. Proper Use of Metric Units • Omit decimal point and 0 when dimension is a whole number • Precede a decimal value that is less than 1 with a 0 • When the value is greater than a whole number by a fraction of a mm, do not place a 0 next to last digit • Exception: when displaying tolerance values

  25. Proper Use of Metric Units • Plus and minus tolerance values have same number of decimal places • Limit tolerance values have same number of decimal points • Unilateral tolerances use a single 0 without a corresponding + or – sign

  26. Inch Dimensions • Decimal inches (IN) • United States (U.S.) customary unit of measure • General note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHES • Follow any millimeter dimensions with mm

  27. Proper Use of Inch Units • Do not precede a value that is less than 1 inch with a 0 • Express a specified dimension to the same number of decimal places as its tolerance • Fractional inches generally indicate larger tolerance

  28. Proper Use of Inch Units • Plus and minus tolerance values have the same number of decimal places • Unilateral tolerances use the + and – sign • The 0 value has the same number of decimal places as the value that is greater or less than 0 • Limit tolerance values have the same number of decimal points

  29. Proper Use of Angular Units • Use decimal or degrees–minutes–seconds format • Angle and tolerance values have the same number of decimal places • Include 0°or 0°0″ when specifying only minutes or seconds, as applicable

  30. Using Fractions • Not as common as decimal inches or millimeters • Architectural and structural drawings • Generally indicate larger tolerance

  31. Arrowheads • Terminate dimension lines and leaders • Three times as long as they are wide • Consistent size • Filled in solid or open

  32. Dimension Line Spacing • First dimension line: • Uniform distance from the object • .375 in. (10 mm) minimum • .5 - 1.0 in. (12 - 24 mm) preferred • Succeeding dimension lines: • Equally spaced • .25 in. (6 mm) minimum • .5 - .75 in. (12 - 20 mm) preferred

  33. Dimension Numerals

  34. Chain Dimensioning • Creates tolerance stacking (tolerance buildup) • Omit one intermediate dimension or the overall dimension

  35. Baseline Dimensioning • Size or location of features controlled from a common reference plane • Reduces possibility of tolerance stacking

  36. Direct Dimensioning • Results in the least tolerance stacking

  37. Dimensioning Symmetrical Objects

  38. Dimensioning Cylinders

  39. Dimensioning Square Features

  40. Preferred Dimensioning Practices • Avoid crossing extension lines • Do not break extension lines when they cross • Never cross extension lines over dimension lines • Break the extension line where it crosses over a dimension line when necessary

  41. Preferred Dimensioning Practices • Never break a dimension line • Break extension lines when they cross over or near an arrowhead • Avoid dimensioning over or through the object • Avoid dimensioning to hidden features

  42. Preferred Dimensioning Practices • Avoid long extension lines • Avoid using any line of the object as an extension line • Dimension between views when possible • Group adjacent dimensions

  43. Preferred Dimensioning Practices • Dimension to views that provide the best shape description • Do not use a centerline, extension line, phantom line, visible object line, or a continuation of any of these lines as a dimension line • Stagger adjacent dimension numerals so they do not line up

  44. Dimensioning Angular Surfaces

  45. Dimensioning Chamfers

  46. Dimensioning Conical Shapes

  47. Dimensioning Hexagons and Other Polygons • Dimension across the flats

  48. Dimensioning Arc Radius

  49. Dimensioning Arc Length

  50. Additional Radius Dimensioning Applications • True radius • TRUE R followed by the actual radius • Controlled radius • CR followed by the radius • Spherical radius • SR followed by the radius

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